TASC5/KASC12 workshop
22-26 July 2019, MIT / Cambridge, USA
Invited speakers should plan for a talk of 25 min plus 5 min for questions. Contributed talks should be 12 min long plus 3 min for questions and invited software presentations should be 20 min plus 5 min for questions. The resolution of the projector format is 16:9. Presentations need to be uploaded onto our computer before the talk, so contact an LOC member at least 2 hours before your talk. Our computers provide standard presentation software for pdf, PowerPoint, KeyNote, LibreOffice and OpenOffice as well as webbrowsers and software for common movie formats. If you have any special requirements, please contact us at tasc5@mit.edu before the conference.
Depending on the number of posters, posters may be displayed throughout the conference (Monday to Friday) or in two blocks. We will provide all hardware required to hang up posters. The space for each poster is a square where each side is $$1.75\times10^{-9}R_{\odot}=122\;\textrm{cm}=4.0\;\textrm{ft}$$ long.
If you like to print your poster on campus, MIT has a print center called copytech on the ground floor of the Stratton Student Center (84 Massachusetts Ave, Cambridge, MA 02139). The print center is on on weekdays only. Depending on the size, a typical poster costs about 100\$. Please make sure that you submit the order at least 2 business days before the conference and we encourage you to call them at (617) 258-0859 to confirm your order and pickup plan. Another option to print your poster is the FedEx Office close to the campus at 600 Technology Square, Cambridge, MA 02139. You can email your poster and call their office at (617) 494-5905 to confirm your order.
If you submitted an abstract before the talk deadline and do not see it listed here, please contact us at tasc5@mit.edu.
Use the table below to view and search abstracts or jump directly to a listing of all talks or posters.
| Type | Author | Title | Authorlist | Affiliations | Abstract | |
|---|---|---|---|---|---|---|
| Type | Author | Title | Authorlist | Affiliations | Abstract |
topic: TESS Mission
schedule: Mon, 9:00
(invited)
George Ricker
MIT
Successfully launched in April 2018, the Transiting Exoplanet Survey Satellite (TESS) is well on its way to discovering thousands of exoplanets in orbit around the brightest stars in the sky. During its two-year prime survey mission, TESS will monitor more than 200,000 bright stars in the solar neighborhood at a two minute cadence for temporary drops in brightness caused by planetary transits. This short cadence is also ideal for detailed asteroseismic studies of a large and varied sample of bright stars. This first-ever spaceborne all-sky transit survey will identify planets ranging in size from Earth-sized to gas giants, orbiting a wide variety of host stars, ranging from cool M dwarfs to hot O/B giants.
The initial TESS all-sky survey is well underway, covering 13 observation sectors in the Southern Ecliptic Hemisphere in Year 1, and 13 observation sectors in Year 2. A concurrent deep survey by TESS of regions surrounding the North and South Ecliptic Poles will provide prime exoplanet targets for characterization with the James Webb Space Telescope (JWST), as well as other large ground-based and space-based telescopes coming online in the next two decades.
The status of the TESS mission as it completes its first year of science operations will be reviewed. The opportunities enabled by TESS’s unique lunar-resonant orbit for an extended mission lasting more than a decade will also be presented.
topic: TESS Mission
schedule: Mon, 9:30
Jon M. Jenkins(1)
(1) NASA Ames Research Center
TESS launched 18-4-2018 to conduct a two-year, near all-sky survey for at least 50 nearby exoplanets for which masses can be. TESS just completed surveying the southern hemisphere, identifying hundreds of candidate exoplanet systems and unveiling a plethora of exciting non-exoplanet astrophysics results, such as asteroseismology, asteroids, and supernova.
The TESS Science Processing Operations Center (SPOC) at NASA Ames Research Center processes the image data downlinked from TESS every two weeks to generate a variety of data products hosted at the Mikulski Archive for Space Telescopes (MAST). For each ~1 month sector, the SPOC calibrates the image data for both 30-min Full Frame Images (FFIs) and up to 20,000 pre-selected 2-min target star postage stamps. Simple aperture photometry and systematic error-corrected flux time series are generated for the 2-min data. The data products also include co-trending basis vectors (CBVs) and calibration files, such as the Pixel Response Functions (PRF). The archival files are modeled after Kepler’s for ease of use, and include Target Pixel Files (TPFs) containing original and calibrated 2-min image data, Light Curve files (LCs) containing the photometric time series for each 2-min target, as well as the Data Validation products. New products derived from the FFIs include light curves for the 2-min targets and CBVs.
The TESS Mission is funded by NASA’s Science Mission Directorate as an Astrophysics Explorer Mission.
topic: Interactive software demo
schedule: Mon, 9:45 (invited software)
Clara E. Brasseur
Space Telescope Science Institute
The Mikulski Archive for Space Telescopes, home of the TESS science data, provides many tools to retrieve and interact with that data. Because of the size of the data set, one of the most powerful and flexible ways is to access the data programmatically. In this presentation I will give a brief overview of the available MAST interfaces followed by an example workflow that demonstrates the power of our programmatic access tools for a specific asteroseismology application.
topic: Early TESS observations
schedule: Mon, 10:45
(invited)
Daniel Huber
University of Hawaii
More than 10 years ago the detection of solar-like oscillations in thousands of cool stars by CoRoT and Kepler kickstarted the space-based photometry revolution of asteroseismology, with numerous breakthrough results on the interior structure and fundamental properties of stars. TESS now enables the powerful extension of asteroseismology of solar-like oscillators to bright stars with independent observational constraints, allowing the systematic investigation of poorly understood physical processes in stellar models such as convective energy transport and mode excitation for hot solar-type stars. In this talk I will review first results on solar-like oscillators with TESS, including an evaluation of the photometric performance of TESS for asteroseismology, a first comparison of the yield of solar-like oscillators between TESS and Kepler/K2, and the discovery of oscillations in individual high-profile targets. I will conclude with an outlook on the expected total yield of asteroseismic detections in the nominal mission, and prospects for asteroseismology of solar-type stars in the extended mission.
topic: Early TESS observations
schedule: Mon, 11:15
Marc Hon (1); Dennis Stello (1,2,3); Sanjib Sharma (2)
(1) School of Physics, UNSW Sydney, Australia; (2) Sydney Institute for Astronomy (SIfA), School of Physics, University of Sydney, Australia; (3)Stellar Astrophysics Centre, Department of Physics and Astronomy, Aarhus University, Denmark
With its all-sky coverage, TESS is monitoring millions of stars in the Galaxy, from which hundreds of thousands are expected to be identified as solar-like oscillators. The detection of such stars is of prime importance for the TASC asteroseismic investigation. Their analysis will enable characterization of exoplanet host stars and of large stellar populations, while also providing insights into stellar structure and evolution. We present the detection of solar-like oscillators from a combined total of over a million stars observed in Sectors 1 and 2 from TESS. We obtain the 'solar-like oscillator yield' and characterize the stars by their seismic log(g) values, which we validate using photometry, spectroscopy, and parallax measurements. Our results demonstrate what we can expect from upcoming data from subsequent Sectors, along with the potential of TESS to inform ensemble studies of stellar populations in the Galaxy.
topic: Early TESS observations
schedule: Mon, 11:30
Timothy R. White (1)
(1) Research School of Astronomy and Astrophysics, Australian National University, ACT 2611, Australia
TESS is observing the brightest stars in the sky, providing a wonderful opportunity for asteroseismology of stars that are already well-studied. Indeed, several such stars have previously been the subject of asteroseismic campaigns from both ground and space. By incorporating complementary observations, stronger constraints may be placed on the physical properties of these stars, opening the way for improvements to stellar models. However, such bright stars provide unique challenges for data processing, and stars brighter than 2nd magnitude are not being calibrated through the TESS Science Processing Operations Center pipeline. Saturation of the TESS cameras produces long bleed columns, which may extend beyond the edge of the CCD and make simple aperture photometry impossible. Additionally, the brightness of these stars and the size of their target pixel masks complicates the determination of accurate background corrections. I will present methods for overcoming these issues, such that asteroseismology of these stars is made possible, and discuss artefacts that may be present in the light curves of these bright stars. Finally, I will present first results from such stars, including the well-known solar-like oscillators beta Hydri and Procyon.
topic: Early TESS observations
schedule: Mon, 11:45
Warrick H. Ball (1, 2); William J. Chaplin (1, 2)
(1) School of Physics and Astronomy, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK; (2) Stellar Astrophysics Centre, Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, DK-8000 Aarhus C, Denmark
HR2562 is a bright F5V star nearly inside TESS's continuous viewing zone. It hosts a directly-imaged $\sim30\,M_\mathrm{Jup}$ brown dwarf orbiting inside a debris disk. The age of such systems is important in understanding whether brown dwarfs form like planets or binary stars (or both) but current estimates for HR2562's age range from essentially zero up to 2 Gyr, which is too uncertain to be very useful. We have been analysing TESS's photometry of HR2562 in the hope of detecting oscillations and thereby constraining the star's age. HR2562 appears in the TESS Asteroseismic Target List as a potential solar-like oscillator but, after 7 sectors of TESS data, no solar-like oscillations are obvious. Instead, it appears HR2562 is a $\gamma$ Doradus variable with oscillation periods similar to the rotation period (as roughly implied by the spectroscopic measurements of $v\sin i\approx30$--$60\,\mathrm{km/s}$). I will report on the current status of our study of this interesting system, based on the TESS data available so far.
topic: Early TESS observations
schedule: Mon, 13:30
(invited)
Earl P. Bellinger
Stellar Astrophysics Centre, Department of Physics and Astronomy, Aarhus University, Denmark
The theories of stellar pulsation and evolution predict the properties of stars throughout the various stages of their existence. These properties include the internal structure of a star at a given age, as well as the frequencies and amplitudes of their pulsations at that age. By combining contemporaneous photometric and spectroscopic measurements from TESS and SONG, it becomes possible to rigorously test these theoretical predictions. In this talk, I will give an overview of some of the experiments we are conducting to make these tests, and I will also present the first results that we have obtained.
topic: Evolutionary diagnostics
schedule: Mon, 14:00
Joel Ong, Sarbani Basu
Yale University
In the asymptotic parameterisation of mode frequencies, the phase function $\epsilon(\nu)$ completely specifies the detailed structure of the frequency eigenvalues. In practice, however, this function of frequency is reduced to a single scalar $\epsilon$, defined, particularly by observers, as the intercept of a least-squares fit to the frequencies against radial order, or via the central value of this function. As a perusal of literature shows, the procedure by which this is done is not unique. We derive a few simple expressions relating various estimators of ε to each other. In particular we demonstrate that a "reduced" functional parameterisation is both easy to evaluate locally, and insensitive to mis-estimations of $\Delta\nu$. It has been shown that a local value of $\epsilon$ can distinguish between stars on the ascending part of the red giant branch and those in the red clump. We demonstrate that this sensitivity to evolutionary stage arises from differences in the local frequency derivative of the underlying phase function; this is ultimately a consequence of differences in internal structure. We apply this to provide a unified view of the Kepler asteroseismic sample.
topic: Evolutionary diagnostics
schedule: Mon, 14:15
James S. Kuszlewicz (1,2); Keaton J. Bell (1,2); Saskia Hekker (1,2)
(1) Max-Planck-Institute for Solar System Research, Justus-von-Liebig-Weg 3, 37077 Goettingen, Germany; (2) Stellar Astrophysics Centre (SAC), Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, Denmark
The eras of TESS and PLATO will provide new challenges for evolutionary state classification of red-giant stars (i.e. red-giant branch vs. core helium burning) given the large number of stars being observed and the short datasets. We propose a new method based upon a supervised classification scheme that uses only "summary statistics" of the timeseries to predict the evolutionary state. Applying this to red giants in the APOKASC catalogue, we obtain a classification accuracy of ~93% for the full 4 years of Kepler data. The method also generalises to shorter datasets; it achieves an accuracy greater than 92% for subsets of the Kepler data with durations that mimic CoRoT (180 days), K2 (80 days) and TESS data (27 days). This work helps to pave the way towards fast, reliable classification of vast amounts of data with a few, well-engineered features. We also show how these features can be applied beyond solar-like oscillators and used in more general stellar classification tasks.
topic: Binary benchmarks
schedule: Mon, 15:30
Daniel R. Hey (1,2); Simon J. Murphy (1,2); Daniel Foreman-Mackey (3)
(1) School of Physics, Sydney Institute for Astronomy (SIfA), The University of Sydney, NSW 2006, Australia; (2) Stellar Astrophysics Centre, Aarhus University, DK-8000 Aarhus C, Denmark ; (3) Flatiron Institute, NYC, USA.
Pulsating stars with coherent modes can be used as clocks. In a binary system, the pulsating star's orbit around the barycentre leads to a change in path length for starlight travelling to Earth. Previous modelling of this phenomenon has relied on segmenting the light curve, which suffers from poor frequency resolution and under-sampling in orbits with high eccentricity. I will discuss a new approach that is applicable to both Kepler and TESS data, which forward models the entire light curve from an arbitrary number of pulsation modes. This technique allows for precise orbital parameter estimation through Bayesian inference. We have written an extensible Python package, Maelstrom, which aims to provide an accessible entrypoint for modelling these systems. I will discuss the usage of Maelstrom, example stars, and how it can be extended to account for eclipsing signals or radial velocity data.
topic: Binary benchmarks
schedule: Mon, 15:45
Jean McKeever; Sarbani Basu
Yale University
Binary star systems provide a unique laboratory to test our understanding of stellar astrophysics. The Kepler mission has observed many binary star systems and provided high-precision photometry. Asteroseismology of solar-like stars provides an independent insight into the interior of a star by examining its oscillations. In this work we model the radial (l=0) and quadrupole (l=2) modes in several binary star systems where one component is an oscillating red giant. Previous work on these types of systems have shown discrepancies in the stellar properties determined by asteroseismic and dynamical methods; and much work has been done lately to improve upon the differences. To improve the asteroseismic estimates, we derive more precise temperatures and metallicities through modeling the stars' spectra with Spectroscopy Made Easy (SME). We also examine our results in the context of the current scaling relations.
topic: Binary benchmarks
schedule: Mon, 16:00
Nathalie Themeßl (1,2); Saskia Hekker (1,2); Andrés García Saravia Ortiz de Montellano (1,2); Alexey Mints (1,3)
(1) Max Planck Institute for Solar System Research, Justus-von-Liebig-Weg 3, 37077 Göttingen, Germany; (2) Stellar Astrophysics Centre, Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, 8000 Aarhus C, Denmark; (3) Leibniz-Institut für Astrophysik Potsdam (AIP), An der Sternwarte 16, 14482, Potsdam, Germany
Red giants showing solar-like oscillations in open clusters and eclipsing binary systems are key objects for testing the asteroseismic scaling relations. Through asteroseismology we can derive their mean densities, surface gravities, masses, and radii. At the same time these parameters can be independently determined from orbital analyses (in the case of binaries) or stellar isochrones (clusters). We analyze three red-giant stars in eclipsing binary systems and about 60 red giants in two open clusters that were observed by the $Kepler$ mission. When using an empirically derived $\Delta\nu$ reference value, we are able to obtain asteroseismic mass and radius estimates that are in agreement with the independent results from binary analyses and cluster isochrones. In addition, we discuss which parameters (e.g. metallicity, mass loss, ...) affect these empirical values.
topic: Binary benchmarks
schedule: Mon, 16:15
Sanjay Sekaran; Andrew Tkachenko; Cole Johnston
Instituut voor Sterrenkunde (IvS), KU Leuven, Celestijnenlaan 200D, B-3001 Leuven, Belgium
Eclipsing binaries are valuable objects of study as the masses and radii of the individual components can often be observationally determined to a precision of $\sim$1% or better. This synergises well with asteroseismology, which enables the derivation of stellar internal properties through the study of stellar pulsations. Combining the information derived from binarity and asteroseismology allows for the simultaneous confrontation of models derived from both stellar structure and evolution, and pulsational excitation theory.
We have identified three F-type eclipsing binaries from the Kepler Eclipsing Binary Catalog (Prsa et al. 2011) that also display g-mode period spacing patterns that are required for asteroseismic modelling: a very rare combination. In particular, we have identified that the eclipsing binary KIC9850387 displays multi-mode period spacing patterns in the Fourier transform of an unprecedented length. Here we present our methodology for the analysis of eclipsing binary pulsators and preliminary results of modelling KIC9850387.
topic: Interactive software demo
schedule: Mon, 16:30 (invited software)
Andrew Tkachenko (1); Rasmus Handberg (2); Mikkel Lund (2)
(1) Institute of Astronomy, KU Leuven; (2) Stellar Astrophysics Centre, Department of Physics and Astronomy, Aarhus University
TESS mission will deliver high-quality light curves for several millions of stars across the entire sky during its nominal 2-year term operations. Although the prime goal of TESS is detection and characterisation of exoplanets, lessons learned from the recently retired Kepler mission allow us to speak about continuing revolution is stellar astrophysics with ample of new opportunities arising from the full-sky nature of the TESS survey. Building on the legacy left by the Kepler mission, the TESS Asteroseismic Consortium (TASC) continues its operations as a unit, popularising active collaboration among scientists all over the world and increasing impact of the TESS mission as a whole by exploring its potential for auxiliary science. In this talk, we will provide an overview of the work that is at the heart of the TASC collaboration and that includes largely automated extraction of light curves and their correction for (instrumental) systematics, as well automated classification of every single extracted light curve according to the type of variability encoded in it. In addition to briefly introducing the overall concept of the pipeline and its individual ingredients, we will demonstrate how the above data products can be accessed by any interested consortium member.
topic: Intermediate-mass stars
schedule: Tue, 8:30
(invited)
Donald Kurtz
Jeremiah Horrocks Institute, University of Central Lancashire
In the HR Diagram where the classical instability strip crosses the main sequence there many types of pulsating stars from which new asteroseismic results are being obtained. This talk will discuss TESS observations of $\delta$ Sct and $\gamma$ Dor stars in comparison with completed and ongoing exploitation of Kepler data. The TESS bright star data include pre-main-sequence stars, Am and $\lambda$ Boo stars, and SX Phe stars (Pop II), which were generally not studied in the Kepler data. A primary result from the TESS A-F star data comes from a systematic survey of ~1200 Ap stars to characterise and to extract asteroseismic inference about the pulsation in roAp stars where strong, global magnetic fields interact with high-overtone p-mode pulsations in the presence of atomic diffusion and atmospheric stratification of elements and ions. New results from TESS show significant, unexplained change in the pulsation axis of HD6532, confirm for the roAp star HD60435 that pulsation mode amplitudes vary on a time scale a short as a day, whereas other roAp stars are stable for decades. Importantly, the large, unbiased, wide survey of Ap stars already shows that these stars are truly rare. The TESS data will map out the roAp instability strip to confront with theoretical predictions. The TESS results are guiding ground-based follow-up to investigate further the many puzzles and opportunities in the study of variable A and F stars.
topic: Intermediate-mass stars
schedule: Tue, 9:00
Vichi Antoci, et al.
Stellar Astrophysics Centre, Aarhus University, Denmark
In this talk I will present TESS’ view of delta Sct and gamma Dor stars observed during the first part of this mission. Although Kepler has provided long uninterrupted data of many and very interesting targets, TESS has the advantage of observing all the bright stars and deliver a nearly uniform and unbiased all-sky survey. The TESS mission provides a unique sample covering all evolutionary stages of A and F pulsators (pre-main sequence, main sequence, post main sequence, Pop II stars) and the entire zoo of chemical peculiar stars (e.g., metal poor, metal-rich, Am and Ap stars, Lambda Boos, … ). Here I will show several examples of delta Sct and gamma Dor stars, including some of the prototypes of different pulsator classes (e.g. SX Phe) and show what we can learn from these stars. In addition I will address a long-standing issue connected to the driving of pulsations in intermediate stars, specifically in delta Sct stars. Models including time-dependent non-local convection treatment show that diffusion of He in the outer envelope plays an important role in the excitation of p modes in delta Sct stars. Using TESS and GAIA data, we can show that there is a good agreement between observations and theory.
topic: Intermediate-mass stars
schedule: Tue, 9:15
Filiz Kahraman Alicavus (1, 2) ; Ennio Poretti (3, 4); Gianni Catanzaro (5); Barry Smalley (6); Ewa Niemczura (7); Monica Rainer (8)
(1) Nicolaus Copernicus Astronomical Center, Bartycka 18, PL-00-716 Warsaw, Poland; (2) Canakkale Onsekiz Mart University, Faculty of Sciences and Arts, Physics Department, 17100 Çanakkale, Turkey; (3) INAF - Fundacion Galileo Galilei, Rambla Jose Ana Fernandez P erez 7, E-38712 Bre na Baja, Tenerife, Spain; (4) INAF – Osservatorio Astronomico di Brera, Via E. Bianchi 46, 23807 Merate (LC), Italy; (5) INAF—Osservatorio Astrfisico di Catania, Via S. Sofia 78, I-95123 Catania, Italy; (6) Astrophysics Group, Keele University, Keele ST5 5BG, UK; (7) Instytut Astronomiczny Uniwersytetu Wrocławskiego Ul. Kopernika 11, 51-622 Wrocław, Poland; (8) National Institute of Astrophysics (INAF), Astronomical Observatory of Brera, Via Brera 28, 20121 Milano, Italy
Gamma Dor and A-F type hybrid pulsators are supposed to have an effective temperature range of about 6500–7500 K. However, the high-quality Kepler data has revealed some gamma Dor and A-F hybrid pulsators hotter than 7500 K. To drive the pulsation mechanism in these pulsators, a sufficient convective envelope is necessary. According to theory in these hot objects the convective envelope shouldn’t be sufficient enough to excite the gamma Dor type pulsations. To explain this unexpected situation, some opinions were proposed such as possible incorrect atmospheric parameters, rapid rotation, chemical peculiarity, and binarity. A detailed spectroscopic and photometric investigation is needed to clarify these opinions. Therefore, we present the conclusions of our detailed spectroscopic and photometric study of twenty-four hot gamma Dor and A-F hybrid candidates. Consequently, we confirm that the hot gamma Dor and A-F hybrid stars exist. The chemical peculiarity and binarity don’t appear to be a possible answer for the existence of these objects. It has been suggested that hot gamma Dor and hybrid stars might be fast rotating slowly pulsating B stars (Balona et al. 2016). The stars in our sample have high vsini value (on average 130 and 190 km/s for gamma Dor and hybrid stars, respectively) but they don’t show B type spectral lines. The result of this study provides new information to improve the understanding of the pulsation mechanism that occurs in the gamma Dor stars.
topic: Intermediate-mass stars
schedule: Tue, 9:30
Juan Carlos Suárez (1,2); Antonio García Hernández (1,2); Roberto Maestre (3); Alejandro Ramón Ballesta (2); José Ramón Rodón (2)
(1) Dept. Física Teórica y del Cosmos. Universidad de Granada. 18071 Granada, Spain; (2) Instituto de Astrofísica de Andalucía (CSIC). Glorieta de la Astronomía s/n. 18006. Granada, Spain; (3) Universidad Internacional de Valencia, E-46021 Valencia, Spain
In the present work we have used Artificial Intelligence to extract both the large separation and rotational splitting of $\delta$ Scuti stars. In particular we have trained a neural network (NN), using the method of depth-wise separable convolution. The NN was trained with 1D-rotating models computed with CESTAM code for a wide range of masses, rotation velocities (slow-to-moderate), and metallicities, representative of A-F stars. The oscillations were computed with the adiabatic code FILOU which takes rotation up to the second-order into account (including near degeneracy and the stellar distortion). The NN was fed simultaneously in four channels with the discrete Fourier transform of the oscillation spectrum (DFT), autocorrelation (AC), histogram of the frequency differences, and the spectrum itself. For the validation sample the NN was able to find the large separation (or its half) and the rotational splitting with a relative error below 10% for more than 70% of the models. We then applied the NN to a sample of well-characterised $\delta$ Scuti stars in eclipsing binary systems (García Hernández et al. 2017), obtaining a similar success rate inferring the large separation and the rotational splitting of the stars. We have applied this methodology to other stars not so well characterised and discuss the results.
topic: Intermediate-mass stars
schedule: Tue, 9:45
Antonio García Hernández (1, 2); Javier Pascual-Granado (2); Juan Carlos Suárez (1, 2); Ádam Sódor (3); Francesc Simó (4); David Pamos (4); Zsófia Bognár (3); Mariel Lares-Martiz (2); Rafael Garrido (2); José Ramón Rodón (2); and the SoFAR team
(1) Universidad de Granada, Dept. Theoretical Physics and Cosmology, 18071, Granada, Spain; (2) Instituto de Astrofísica de Andalucía (CSIC), Glorieta de la Astronomía S/N, 18008, Granada, Spain; (3) Konkoly Observatory, MTA CSFK, Konkoly Thege M. u. 15-17., H-1121 Budapest, Hungary; (4) Universidad Internacional de Valencia, E-46021 Valencia, Spain
We have studied the period-luminosity-color (PLC) diagram of a sample of more than 3000 $\delta$ Scuti and $\gamma$ Doradus stars (including hybrids). We also compared these observations with a grid of rotating oscillation models. We confirm the very recent result from Ziaali et al. 2019 and go further identifying the fundamental radial mode for the $\delta$ Scuti in our sample. Our grid show that this is possible without any doubt because the PLC relation we found is independent of the stellar rotational velocity and metallicity. In fact, the frequency with the highest amplitude of a banch of stars in the sample gather around the fundamental radial mode relation. But the comparison with $\gamma$ Doradus also reveals that the widely used criterion for classifying both types of pulsators need to be revised. We propose a new criterion based in our findings. More consequences are derived from this diagram, using known facts as the P0/P1 relation and the large separation-P0 relation.
topic: Intermediate-mass stars
schedule: Tue, 10:45
(invited)
Tim Bedding
School of Physics, University of Sydney
Efforts to use $\delta$ Scuti stars for asteroseismology have been limited by the difficulty in recognising patterns in their oscillation spectra and assigning mode identifications. The problems are compounded by rapid rotation and departures from asymptotic spacings. We have identified a subset of high-frequency $\delta$ Scuti stars that show remarkably regular oscillation spectra, allowing us to identify oscillation modes and compare directly with theoretical models.
topic: Intermediate-mass stars
schedule: Tue, 11:15
Gang Li (1); Timothy Van Reeth (1, 2); Timothy R Bedding (1); Simon J Murphy (1); Victoria Antoci (3); Rhita-Maria Ouazzani (4)
(1) Sydney Institute for Astronomy (SIfA), School of Physics, 2006 University of Sydney, Australia; (2) Institute of Astronomy, KU Leuven, Celestijnenlaan 200D, B-3001 Leuven, Belgium; (3) Stellar Astrophysics Centre, Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, DK-8000 Aarhus C, Denmark; (4) LESIA, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Universités, UPMC Univ. Paris 06, Univ. Paris Diderot,Sorbonne Paris Cité, 5 place Jules Janssen, 92195 Meudon, France
We conducted an observational study on the $\gamma$ Dor stars. These stars pulsate mainly in g-modes and r-modes, showing period spacing patterns in the power spectra. The period spacing patterns are sensitive to the chemical composition gradients and the near-core rotation, hence they are valuable for understanding the stellar interior.
We identified period spacing patterns in about 600 $\gamma$ Dor stars from the 4-yr Kepler data. All the stars pulsate in dipole g-modes, while about 30\% of stars also show clear patterns for quadrupole g-modes and 16\% of stars present r-mode patterns. The periods, the period spacings, and the deviations from uniform spacings are measured accurately. We find these three observables guide the mode identifications and can be used to estimate the near-core rotation rate.
Using the Traditional Approximation of Rotation (TAR), we can measure the asymptotic spacing, the near-core rotation rate, and the radial order. Our results show that the stars rotate more slowly than predicted by theory, and the rotation distribution is bimodal for unclear reasons. Comparing the near-core rotation with the surface modulation signals, we detected the core-to-surface rotation profiles in about 10\% stars. The interiors rotate faster than the cores in most stars, but by no more than 5\%. We also find a possible evolutionary effect about the rotation profile.
topic: Intermediate-mass stars
schedule: Tue, 11:30
Joey S. G. Mombarg (1); Aaron Dotter (2); Anne Thoul (3); Conny Aerts (1, 4)
(1) Institute of Astronomy, KU Leuven, Leuven, Belgium; (2) Harvard-Smithsonian Center of Astrophysics, Cambridge, USA; (3) Institut d'Astrophysique et de Géophysique, Université de Liège, Liège, Belgium; (4) Department of Astrophysics, IMAPP, Radboud University, Nijmegen, The Netherlands
One of the biggest enigmas of stellar evolution concerns the transport of chemical elements. As this process is already ill-constrained during the core-hydrogen burning phase, the uncertainties that are introduced propagate into models of more evolved stars. The current state-of-the-art models are not able to predict the observed oscillation frequencies in intermediate-mass stars with their uncertainties. In this talk, we discuss the effect of atomic diffusion (including radiative levitation) on the frequencies of gravity modes and its implications for forward seismic modelling of intermediate-mass stars. Our results show significant differences in frequencies when including atomic diffusion, resulting in different derived masses, ages and metallicities. We will present our findings of our improved forward modelling scheme applied to a slowly rotating pulsator.
topic: Intermediate-mass stars
schedule: Tue, 11:45
Kuldeep Verma(1); Víctor Silva Aguirre(1)
(1) Stellar Astrophysics Centre, Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, DK-8000 Aarhus C, Denmark
Recent developments in asteroseismology, thanks to CoRoT and Kepler space missions, have provided numerous constraints on the stellar properties. Among them is the unprecedented constraint on the surface helium abundance of F and G stars from the identification of oscillatory signature of helium ionization in the observed frequencies. It is possible to use the observed amplitude of oscillatory signature to study the non-standard physical processes that compete against atomic diffusion and are responsible for the abundance anomalies observed in AmFm stars. We identified three most promising F stars for such study from LEGACY sample: KIC 2837475, 9139163 and 11253226. For these stars, the standard models of atomic diffusion predict large settling (or complete depletion) of the surface helium. Assuming turbulence at the base of convection zone is competing against atomic diffusion, we found an envelope mixed mass of approximately $5 \times 10^{-4}$M$_\odot$ necessary to reproduce the observed amplitude for all the three stars. This is much larger than the mixed mass of the order of $10^{-6}$M$_\odot$ found in the previous studies performed using the measurements of the heavy element abundances. This demonstrates the potential of using the combined information from the observed helium signature and measured heavy element abundances to identify the most important physical processes competing against atomic diffusion, and opens window for significantly more accurate stellar ages.
topic: Tides
schedule: Tue, 13:30
Zhao Guo (1,2); Jim Fuller (3); Avi Shporer (4); Kelly Hambleton (5); Howard Isaacson (6)
(1)Center for Exoplanets and Habitable Worlds, 525 Davey Laboratory, The Pennsylvania State University, University Park, PA 16802;
(2)Copernicus Astronomical Center, Polish Academy of Sciences, Bartycka 18, 00-716 Warsaw, Poland ; (3)TAPIR, Mailcode 350-17, California Institute of Technology, Pasadena, CA 91125; (4)Department of Physics and Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, Cambridge, MA 02139; (5)Department of Astrophysics and Planetary Science, Villanova University, 800 East Lancaster Avenue, Villanova, PA 19085; (6)Department of Astronomy, University of California, Berkeley CA 94720
More than half of all stars reside in binaries and tides can have a significant effect on stellar oscillations. In the first version of the classical textbook Nonradial Oscillations of Stars by Wasaburo Unno et al. (1979), there is a whole chapter on tidally forced oscillations. However, it was removed in the second version (1989), probably owing to the notion that such oscillations are difficult to be observed in practice. Thanks to precise measurements of the space missions (Kepler, BRITE, TESS), we are now able to observe unambiguously the manifestation of (dynamical) tides: tidally excited oscillations (TEOs).
Observationally, we measure the fundamental parameters of four Kepler heartbeat binaries with TEOs by combining the Kepler light curves and Keck HIRES spectra. These accurate measurements are the prerequisite for subsequent theoretical studies.
Theoretically, we model the amplitude and phase of TEOs in the regime of linear theory. We also examine the temporal evolution of the binary orbit and the TEOs and identify the responsible dissipation mechanism. We try to explain the non-orbital-harmonic TEOs in the regime of non-linear three/multi-mode-coupling. Theoretical mode-coupling thresholds and observed parent mode amplitudes are compared.
In the end, we discuss the challenges posed by these observations in tidal asteroseismology.
topic: Tides
schedule: Tue, 13:45
P. G. Beck (1), S. Mathis (2), F. Gallet (3), C. Charbonnel (3), M. Benbakoura (2), R. A. Garcia (2), J.-D. do Nascimento (4,5) and J. Vos (6)
(1) Institute for Physics, Universität Graz, Austria; (2) Commissariat à l'Énergie atomique et aux Énergies, Paris-Saclay, France; (3) Observatoire de l’université de Genève, Switzerland; (4) Harvard-Smithsonian Center for Astrophysics, USA; (5) Departamento de Física, Universidade Federal do Rio Grande do Norte, Natal, RN, Brazil; (6) Institut für Physik und Astronomie, Universität Potsdam, Germany
Tidal interactions are one of the main physical mechanisms that govern the redistribution of angular momentum in planetary and binary systems. They determine the pace of a system’s evolution towards the equilibrium state of circularized orbits and synchronized and aligned stellar rotation. Various observational signatures, associated with dissipation processes of tidal kinetic energy, are known: surface distortion, tidally-induced acoustic & tidal inertial waves. While all three observational manifestations of tidal interactions are found in main-sequence binaries, only surface distortion has been detected in binaries hosting a red-giant primary. Therefore, the existence and efficiency of other dissipation processes remains an open question.
So far, in red-giant binaries tidal interactions have only been analyzed in a handful of individual binary systems. We present ensemble studies of tidal interactions in all 31 known red-giant binaries, observed by Kepler. We show that even if the dynamical tide could propagate in the giant’s convective envelop as inertial wave, its contribution to the overall dissipation budget is negligible. Through modelling of the system’s history and the primary component’s evolutionary state, we highlighted that tidal efficiency is well characterized by current theory despite the recent claims of overestimation by two orders of magnitude of the classical tidal theory, that is required to solve the eccentricity problem of post-AGB and sdB stars.
topic: Tides
schedule: Tue, 14:00
Cole Johnston (1); Dominic Bowman (1); Conny Aerts (1); Andrew Tkachenko (1)
Institute of Astronomy, KU Leuven, Belgium
Tidal forces caused by the gravitation of a close companion in a binary system can produce extreme structural changes and deviations from secular stellar evolution. While the broader evolutionary consequences of tidal interactions are understood in a general sense, the extent of the altercations to internal stellar structure caused by tidal interactions have almost no observational characterization. Although classical asteroseismology has produced a renaissance in the understanding of internal stellar structure and evolution, tidal asteroseismology is still in its infancy. In this talk we discuss the diversity of tidally influenced pulsations discovered so far in the TESS sample, and present the results of using tidal asteroseismology to detect perturbations in stellar structure caused by tides.
topic: Massive stars
schedule: Tue, 14:15
(invited)
May Gade Pedersen(1)
(1) Institute of Astronomy, KU Leuven, Celestijnenlaan 200D, 3001 Leuven, Belgium
Both the chemical and dynamical evolution of the Universe as a whole is largely guided by the life of massive stars. These stars are responsible for the production of heavy elements in their cores through nuclear burning cycles, and chemically enrich their environment through strong stellar winds and supernova explosions. However, in spite of their importance, major shortcomings prevail in the theory of stellar structure and evolution of massive stars, arising from the lack of precise calibrations of their internal properties. Such properties are the transport of chemical elements and angular momentum, which directly impact the internal structure of stars and hence their evolution.
Asteroseismology provides a promising tool for calibrating the internal properties by studying stellar pulsations which probe different depths of the stellar interior. Such calibrations rely on high precision on the pulsation frequencies achieved through high-precision, high-cadence and long time-base space photometry. With this talk we present results already achieved with the Kepler space mission for a small number of massive stars, and discuss the promising prospects of the TESS space mission for the field of asteroseismology of massive stars.
topic: Massive stars
schedule: Tue, 14:45
Dominic M. Bowman; et al.
Instituut voor Sterrenkunde, KU Leuven, Celestijnenlaan 200D, 3001 Leuven, Belgium
Massive stars end their lives as a supernova and form a black hole or neutron star. Supernovae enrich the interstellar medium and impact the next generation of star formation and the evolution of the host galaxy. However the mass of the compact remnant and the supernova chemical yield depend on the internal physics of the progenitor star, which are currently not well-constrained from observations. The large uncertainties in the models of massive star interiors accumulate during stellar evolution, and the lack of a robust theory is particularly pertinent for blue supergiant stars. Asteroseismology allows us to probe stellar interiors, yet inference from blue supergiants was limited by a dearth of detected pulsations in these stars before K2 and TESS space photometry.
In this talk, we report the discovery of coherent pulsation modes and stochastic low-frequency gravity waves in numerous blue supergiants, which allow their interior properties to be mapped from the main sequence to the later stages of their evolution. Asteroseismic modelling provides important constraints on ages, core masses, interior mixing, rotation and angular momentum transport, which are essential input parameters in stellar evolution models. The discovery of pulsational variability in space photometry of blue supergiants provides a necessary first step towards a data-driven empirical calibration of theoretical evolution models for the some of most massive and short-lived stars in the Universe.
topic: Massive stars
schedule: Tue, 15:30
Derek Buzasi (1); Lindsey Carboneau (1)
(1) Florida Gulf Coast University
Massive stars play an outsized role in the dynamics of the universe through their roles in chemical enrichment and as Type II supernova progenitors. Models of their stellar structure and evolution are limited by our understanding of processes such as angular momentum transport, internal rotation profiles, chemical mixing, and magnetic fields. However, improving our understanding of these objects remains fundamental to our knowledge of diverse astrophysical topics including star formation, stellar winds, and the evolution of the interstellar medium. Asteroseismology has become a key component of this understanding, as many massive stars display oscillations which are accessible to telescopes of relatively small aperture due to both the intrinsic brightness and the relatively large oscillation amplitudes of these stars.
2019 marks the twentieth anniversary of space-based asteroseismology, epitomized by missions such as WIRE, MOST, CoRoT, Kepler, BRITE, and TESS, and we are entering a regime where many massive stars have been observed multiple times during different epochs by multiple missions. Given the speed of evolutionary change at the top of the main sequence, such long temporal baselines may allow the possibility of observing evolutionary changes directly. We will describe ongoing projects to make use of multiple space-based photometric data sets to search for such signatures, discuss what we might reasonably expect to learn, and suggest projects for future observers.
topic: Massive stars
schedule: Tue, 15:45
Tao Wu; Yan LI
Yunnan Observatories, Chinese Academy of Sciences, 396 Yangfangwang, Guandu District, Kunming, 650216, P. R. China
The Slowly Pulsating B-type (SPB) stars are the upper main-sequence stars on the HR diagram. Their oscillations are high-order, low-degree g-mode and can be used to probe the structure of the radiative zone near the outer boundary of the convective core and constrain the chemical mixing in stellar interiors. In SPB stars, the period spacing periodically varies with periods. The frequency of such periodical variations changes with the stellar evolutionary status. Therefore, it has been regarded as a signature of the chemical composition gradient beyond the convective core. Based on theoretical calculations, we find that the variation frequency of the period spacings ($f_{\Delta P}$) is related to the width of the $\mu$-gradient region on the buoyancy radius ($\Lambda_{\mu}$) with the relation of $f_{\Delta P}\sim0.5\Lambda_{\mu}$. This indicates that the variation frequency $f_{\Delta P}$ is sensitive to the central hydrogen mass fraction $X_{\rm C}$ (i.e., the evolutionary status). Finally, we find that the variation frequency $f_{\Delta P}$ and the means of the period spacings $\langle\Delta P\rangle$ can be used to construct a new C-D-like diagram ($f_{\Delta P}$ vs. $\langle\Delta P\rangle$) which can be used to roughly estimate the stellar evolutionary stages, i.e., central hydrogen mass fraction $X_{\rm C}$, and to approximately constrain stellar mass for SPB stars.
topic: Massive stars
schedule: Tue, 16:00
Lucas Viani
Yale University
Convective overshoot in high mass stars is an unknown quantity and hence a source of uncertainty when determining stellar properties. Whether the amount of overshoot is constant or mass dependent is not completely known, even though models often assume a mass-based trend. In this work we use stars observed by Kepler to investigate the relationship between various stellar properties and the amount of overshoot needed to properly model a given star. We also examine whether, and how, different implementations of overshoot in models makes a difference. We present the results of our investigation, with emphasis on how overshoot changes with stellar properties.
topic: Interactive software demo
schedule: Tue, 16:15 (invited software)
Jessie Dotson (1); Christina Hedges (1,2); Geert Barentsen (1,2); Michael Gully-Santiago (1,2); Nick Saunders (1,2); Ann Marie Cody (1,2)
(1) NASA Ames Research Center; (2) BAERI
Lightkurve is a community-developed, open-source Python package which offers user-friendly and accessible way to analyze data from NASA’s Kepler, K2, and TESS missions. The package is supported by a rich series of tutorials which aim to lower the barrier for all potential users of data from NASA’s exoplanet space telescopes. Lightkurve functionality includes easy data retrieval, interactive aperture selection, custom aperture photometry and systematics removal. This tutorial will introduce the functionality available in lightkurve and demonstrate its use on TESS data.
topic: Interactive software demo
schedule: Tue, 16:40 (invited software)
Oliver J. Hall (1, 2) and the Lightkurve Collaboration
(1) School of Physics and Astronomy, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK; ; (2) Stellar Astrophysics Centre, Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, DK-8000 Aarhus C, Denmark
The Python package ‘lightkurve’ offers a user-friendly way to interact with and analyse time series data from the Kepler and TESS missions. It lowers the barrier for users to perform aperture photometry, find planets, and perform basic asteroseismic analysis. In this talk I will give a live demonstration of how to take a TESS image of a target and produce a periodogram of its frequency spectrum.I will demonstrate lightkurve’s capability to derive seismic parameters and calculate a rudimentary mass and radius. Along the way I will showcase lightkurve’s range of customisation options that can help you investigate your favourite star faster than ever. Lightkurve is open source, has a large community of authors and provides a range of tutorials, which are perfect for established astronomers and new students.
topic: Stellar activity
schedule: Wed, 8:45
(invited)
Rachael Roettenbacher (1)
(1) Yale Center for Astronomy and Astrophysics, Yale University, CT, USA
The magnetic fields of cool stars lead to a variety of stellar activity phenomena, some of which are readily observed in light curves. These include the modulation of starspots rotating in and out of view and the rapid rise and exponential decay of stellar flares. These signs of stellar activity can be used to investigate the nature of stellar magnetism and more general stellar parameters. Photometric space telescopes such as Kepler and TESS are excellent resources for investigating the evolution of stellar activity over time and across the Hertzsprung-Russell diagram through starspots and flares. In its first year, TESS has already provided observations used to investigate starspots and flares, adding to the vast amount of stellar activity available in the Kepler and K2 archives. New results on the correlation between starspots and flares in different types of stars and measuring differential rotation with starspots, as well as the prospects for TESS's impact on the field of stellar activity will be discussed.
topic: Stellar activity
schedule: Wed, 9:15
Ângela R. G. Santos (1); Rafael A. García (2); Savita Mathur (3); Lisa Bugnet (2); Travis S. Metcalfe (1); Gregory V. A. Simonian (4); Jennifer L. van Saders (5); Marc H. Pinsonneault (4)
(1) Space Science Institute, Colorado, USA; (2) IRFU, CEA, Université Paris-Saclay, France; (3) Instituto de Astrofísica de Canarias, Tenerife, Spain; (4) Department of Astronomy, The Ohio State University, Ohio, USA; (5) Institute for Astronomy, University of Hawai'i, Hawai, USA
From stellar brightness variations due to dark starspots, one can learn about surface rotation and the magnetic properties of stars. Rotation itself is an important ingredient for the dynamo mechanism, and is also used as a diagnostic for stellar age. In this work, we analyze the spot modulation in light-curves for main-sequence and subgiant stars observed by Kepler main-mission. We analyze four data sets: KADACS (García et al. 2011) time-series obtained for 20-, 55-, and 80-day filters; and PDC-MAP (e.g. Jenkins et al. 2010) time-series. The rotation estimates are retrieved through a combination of wavelet analysis and the autocorrelation function of light-curves (e.g. Mathur et al. 2010; García et al. 2014, Ceillier et al. 2016, 2017). Reliable rotation periods are determined by comparing the rotation estimates obtained from the different diagnostics and for the different time-series. We recover rotation periods for more than $60\%$ of the targets. For those, we also study the photometric activity level and lifetime of active regions. We find the rotation rate to increase with effective temperature and mass, while the photometric activity proxy increases towards fast rotators. Active region lifetimes are found to be longer with increasing rotation rate and photometric activity. In this analysis we also identify potential polluters, such as mis-classified Red Giants, classical pulsator candidates, and photometric pollution of light-curves.
topic: Stellar activity
schedule: Wed, 9:30
Alexandra E. L. Thomas (1,2); William J. Chaplin (1,2); Guy R. Davies (1,2); Rachel Howe (1,2); Ângela R. G. Santos (3); Yvonne Elsworth (1,2); Andrea Miglio (1,2); Tiago Campante (4,5); Margarida S. Cunha (4)
(1) School of Physics and Astronomy, University of Birmingham, Edgbaston, Birmingham, B15 2TT, UK; (2) Stellar Astrophysics Centre, Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, DK-8000 Aarhus C, Denmark; (3) Space Science Institute, 4750 Walnut Street, Suite 205, Boulder, CO 80301, USA; (4) Instituto de Astrofísica e Ciências do Espaço, Universidade do Porto, Rua das Estrelas, PT4150-762 Porto, Portugal; (5) Departamento de Física e Astronomia, Faculdade de Ciências da Universidade do Porto, Rua do Campo Alegre, PT4169-007 Porto, Portugal
We present a new method for determining the location of active bands of latitude on solar-type stars, which uses stellar-cycle-induced frequency shifts of detectable solar-like oscillations. When near-surface activity is distributed in a non-homogeneous manner, oscillation modes of different angular degree and azimuthal order will have their frequencies shifted by different amounts. We use this simple concept, coupled to a model for the spatial distribution of the near-surface activity, to develop two methods that use the frequency shifts to infer minimum and maximum latitudes for the active bands. We verify that we can draw accurate inferences in the solar case and then apply our methods to Kepler data on the solar analogue HD173701, finding that its active bands straddle a much wider range in latitude than do the bands on the Sun. This work was published in the Monthly Notices of the Royal Astronomical Society, March 2019.
topic: Stellar activity
schedule: Wed, 9:45
Savita Mathur (1,2); Rafael A. Garcia (3); Lisa Bugnet (3); Angela R. G. Santos (4); Netsha Santiago (5); Paul G. Beck (6)
(1) Instituto de Astrofisica de Canarias, La Laguna, Tenerife, Spain; (2) Departamento de Astrofisica, Universidad de La Laguna, Tenerife, Spain; (3) IRFU, CEA, Universite Paris-Saclay, Gif-sur-Yvette, France; (4) Space Science Institute, Boulder, CO, USA; (5) University of Puerto Rico, Cayey, Puerto Rico; (6) University of Graz, Austria
More than 2,000 stars were observed in short cadence for one month, during the survey phase of the Kepler mission. The asteroseismic analysis of those stars led to the detection of solar-like oscillations in only ~540 stars. Chaplin et al. (2011) explained the lack of detection in most of the other stars as a consequence of their high surface magnetic activity. However the sample of stars studied was polluted with many classical pulsators and red giants. In this work we re-visit the analysis done on those stars after cleaning the sample from stars with newly detected oscillations (solar-like pulsators, red giants or classical pulsators) based on the latest DR25 lightcurves. We re-analysed the remaining main-sequence solar-like stars in terms of rotation and magnetic activity using the methods described by Garcia et al. (2014). By doing so, we retrieve the most reliable rotation periods and the associated magnetic activity proxy. While close to half of this sample has an Sph value larger than the one of the Sun, we find that a large fraction of stars without oscillations detected have a low magnetic activity level. We investigate on the origin of these missing detections using new spectroscopic observations of those stars (in particular in terms of metallicity, inclination angles). This work is key to better predict the yield of detection of acoustic modes for missions such as TESS and PLATO, in order to better characterize planet-hosting stars in particular.
topic: Compact pulsators
schedule: Wed, 10:45
(invited)
S. Charpinet (1) and the TASC WG8 team
(1) IRAP/CNRS/Université de Toulouse
The TESS satellite has been delivering, since early December 2018, a wealth of high-quality photometric data for a multitude (~1500 to date) of evolved compact stars, mostly white-dwarf and hot-subdwarf stars, proposed for monitoring as part of the TASC WG8 2mn-cadence variablity survey. This leads to a harvest of highly improved data and new discoveries for fields ranging from the study of evolved compact binaries to stellar pulsations and asteroseismology. In this talk, I will provide a brief overview of the oustanding TESS data gathered so far for various types of evolved compact stars. I will also present first results obtained from detailed analyses of specific TASC WG8 targets that outline the great potential of this mission for "TESSting" ultimate stages of stellar evolution.
topic: Compact pulsators
schedule: Wed, 11:15
M. H. Montgomery (1); J. J. Hermes (2); B. H. Dunlap (1); D. E. Winget (1)
(1) University of Texas and McDonald Observatory, Austin, TX, USA; (2) Department of Astronomy, Boston University, Boston, MA, USA
The standard theory of pulsations deals with the frequencies and growth rates of infinitesimal perturbations in a stellar model. Driven modes should have exponentially increasing amplitudes. The observed nearly constant amplitudes are evidence that nonlinear mechanisms inhibit their growth. Models predict that the mass of DAV convection zones is very sensitive to temperature (i.e., $M_{\rm CZ} \propto T_{\rm eff}^{-90}$), so that even “small amplitude” pulsators may experience significant nonlinear effects. In particular, the outer turning point of finite-amplitude g-mode pulsations varies with the local surface temperature, leading to reflected waves that are slightly out of phase with the requirements for a standing wave. This can lead to a lack of coherence of the mode and a reduction in its global amplitude. We compute the size of this effect for specific examples and discuss the results in the context of Kepler and K2 observations.
topic: Compact pulsators
schedule: Wed, 11:30
Weikai Zong (1); Stephane CHARPINET (2); Gerard VAUCLAIR (2); Jian-Ning FU (1)
(1) Department of Astronomy, Beijing Normal University, Beijing 100875, P.R. China; (2) IRAP, Université de Toulouse, CNRS, UPS, CNES, 14 avenue Edouard Belin, F-31400Toulouse, France
With Kepler photometry, frequency and amplitude of oscillation modes can be measured with unprecedented high precision for particular short-cadence targets such as pulsating hot B subdwarfs and white dwarfs. In this context, we report the results of our sustained efforts, since 2013, to analyse mode behaviours in those compact stars. Several aspects are addressed: 1) we observed that oscillation modes generally exhibit amplitude and frequency modulations (AM/FM) in many compact pulsators; 2) coherent AM/FM occur on rotational multiplets in both sdB and white dwarfs, which can be the clear-cut signature of nonlinear resonant mode interactions; 3) the modulation patterns can be very helpful for identifying modes prior to seismic modelling; and 4) frequency modulations can perturb accurate measurements of secular (evolutionary) or regular (due to the presence of a stellar or planetary companion) period changes in the pulsations over long time baselines. We also discuss the difficulties of measuring precise intrinsic AM/FMs even with up to four years of continuous photometry. Such phenomena can also thoroughly be studied in many other types of pulsating stars spanning the whole HR diagram, using the photometry available from the Kepler legacy and from the ongoing TESS mission.
topic: Compact pulsators
schedule: Wed, 11:45
Zach Vanderbosch (1,2); J.J. Hermes (3); Mike Montgomery (1,2); Don Winget (1,2)
The University of Texas at Austin; McDonald Observatory; Boston University
Pulsating white dwarfs are now known to undergo outburst-like phenomena, events characterized by mean flux increases of $2-15\:\%$ which recur irregularly on 1 to 80+ day timescales. The continuous and long-time baseline Kepler and K2 observations provide vital information on the recurrence and duration timescales and relative flux enhancements for outbursts, but we still lack spectroscopy and/or multi-color photometry from the ground to inform us of surface temperatures and line velocities during outburst. These observations will be crucial for further constraining the physical nature of outbursts and for comparison with the parametric resonance theory thought responsible for these events. We report here on the first such ground-based observations of an outburst in a Helium atmosphere white dwarf (SDSS J085202.44+213036.5) that was also observed in three separate K2 campaigns (EPIC 212072946). We obtained multi-color time series photometry from McDonald Observatory demonstrating this is the largest outburst yet seen in a white dwarf with a mean flux increase exceeding $30\%$ and maximum brightness variations in excess of $80\%$. In addition, mode frequencies seen during outburst match the high-frequency modes observed during quiescence throughout each K2 campaign. We also present our current efforts at utilizing the Zwicky Transient Facility's real time alerts to obtain more multi-color information from the ground during outbursts.
topic: Galactic archaeology
schedule: Thu, 8:30
(invited)
Cristina Chiappini
Leibniz-Institut für Astrophysik Potsdam (AIP)
Because most stars carry in their outer envelopes the chemical composition inhered at birth, it should be possible to map the star formation history in different parts of the Milky Way by measuring, for stars of different ages, a large array of chemical elements covering different nucleosynthetic sites. This goal seems to be still reachable even in the presence of radial stellar mixing, i.e., the fact that stars can move away from their birth places, loosing most of their kinematical memory. We show how the combination of detailed multi-dimensional chemical analysis and precise ages can have an great impact on our current understanding of the formation of the MW, and especially of its oldest populations, such as halo, thick disk and bulge. After illustrating the impact that asteroseismology already had this field with results obtained from the CoRoT and Kepler, we focus on the most recent results based on K2 and TESS observations. In particular, I will describe a pilot project that demonstrates that synergies between asteroseismology and spectroscopy can lead to a breakthrough in obtaining ages for metal-poor halo stars. These results will be discussed in the context of Gaia DR2 and future multi-object spectroscopy such as 4MOST.
topic: Galactic archaeology
schedule: Thu, 9:00
Dennis Stello (1); Victor Silva Aguirre (2); and the WG7 team
(1) UNSW Sydney (Australia); (2) Aarhus University
In this talk we will present the first WG7-wide effort to estimate the stellar radius, mass, and age of red giants observed by TESS. Using a selection of over a dozen `fast-track’ red giants spanning a range in evolutionary stages from the low luminosity red giant branch to just after the red clump, this first WG7 paper demonstrates the potential for performing asteroseismic inferences on giants observed for one month with TESS. Since most TESS stars will be observed for one month, our results showcase the prospects for using TESS to inform Galactic archaeology studies across most of the sky; with an emphasis on the interplay between the thin and thick disks of the Milky Way. We will put our results into perspective of those from K2 and Kepler.
topic: Galactic archaeology
schedule: Thu, 9:15
Ditte Slumstrup ; Victor Silva Aguirre
Stellar Astrophysics Centre, Aarhus University
The young alpha-rich stars have previously been detected in the Kepler and CoRoT fields but cannot be explained by standard chemical evolution models of the Milky Way. Current theories suggest these stars could be evolved blue stragglers, which means their apparent young age could be a consequence of mass transfer or mergers in binary systems, or they could be truly young and have migrated from other parts of the Galaxy with different chemical composition such as near the Galactic bar. With this talk I will present a study on the kinematics and chemical composition of this peculiar population to address the question of their origin. For this we use APOGEE spectra, Gaia DR2 data and asteroseismic data from Kepler, K2 and CoRoT.
topic: Galactic archaeology
schedule: Thu, 10:45
Marc H. Pinsonneault (1); Joel C. Zinn (1); Dennis Stello (2); Daniel Huber (3)
(1) Department of Astronomy, The Ohio State University, Columbus, OH 43210, USA; (2) School of Physics, University of New South Wales, NSW 2052, Australia; (3) Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822, USA
Asteroseismology makes powerful predictions about stellar masses and radii. We demonstrate that the asteroseismic radii derived from Kepler first ascent red giants are in excellent agreement with radii derived independently from a combination of photometry, APOGEE spectroscopy and Gaia astrometry. We critically test different methods for inferring stellar properties and argue that systematics in the absolute radius scale are currently at the 2 \% level. We see hints of deviations from scaling relation behavior in the low metallicity and luminous red giant domains. We argue that they represent metallicity effects in the frequency of maximum power scaling relation in the former case and a combination of model atmosphere and non-adiabatic effects in the latter case.
topic: Galactic archaeology
schedule: Thu, 11:00
Samuel Grunblatt(1), Daniel Huber(1), Eric Gaidos(2), Tim White(3)
(1) Institute for Astronomy, University of Hawaii; (2) Department of Geology and Geophysics, University of Hawaii; (3) Research School of Astronomy and Astrophysics, Australian National University
Measuring precise and accurate stellar radii and temperatures is of utmost importance to the transiting exoplanet and galactic archaeology communities, yet both communities rely on calibration of indirect methods to determine these properties. Here we present the largest sample of interferometric and spectrophotometric data of oscillating red giants to date in order to calibrate effective temperature and radius relations with fundamental observational constraints. Using a calibration based on angular diameters from the CHARA array and spectrophotometry from UH88 and IRTF on Maunakea we measure empirical effective temperatures and bolometric fluxes for ~400 red giant branch stars, which we combine with photometric colors to recalibrate color-temperature relations for giant stars using observed spectra for the first time. We then use bolometric flux estimates and Gaia parallaxes to determine stellar radii independent of asteroseismology, allowing investigation of previous controversial claims of systematic offsets in asteroseismic scaling relations. This recalibration of asteroseismic and color-temperature relations is critical for accurate galactic archaeology and exoplanet science, two of the driving science cases for K2 and TESS.
topic: Galactic archaeology
schedule: Thu, 11:15
Tanda Li (1,2); Tim Bedding (1,2); Dennis Stello (3); Jørgen Christensen-Dalsgaard (2); Yaguang Li (4)
(1)Sydney Institute for Astronomy (SIfA), School of Physics, University of Sydney, NSW 2006, Australia; (2)Stellar Astrophysics Centre, Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, DK-8000 Aarhus C, Denmark; (3)School of Physics, University of New South Wales, Australia; (4)Department of Astronomy, Beijing Normal University, Beijing, China
Detailed modelling of stellar oscillations is able to give precise estimates for stellar ages, however, inferred results are model dependent. When we studied the {\em Kepler} and SONG subgiants, we found that their ages determined by the detailed modelling are not greatly correlated to the input helium fraction and the mixing-length parameter. Moreover, different stellar codes gave similar results when input metallicities are same, says that ages of subgiants are less model dependent than main-sequence stars and red giants and this tend to be a big advantage of subgiants. Ages constrained by individual oscillation frequencies of {\em Kepler} and SONG subgiants show high precision with an average uncertainty of 10%. A follow-up work on the M67 evolved stars also showed that the seismic-determined age of the subgiant is a good estimate for the age of the cluster.
topic: Galactic archaeology
schedule: Thu, 11:30
(invited)
Katrien Kolenberg (1,2); Robert Szabo (3); Laszlo Molnar (3); Emese Plachy (3); and the TASC RR Lyrae and Cepheid working group
(1) Dept. of Physics, University of Antwerp, Belgium; (2) Dept. of Physics and Astronomy, KU Leuven, Belgium; (3) Konkoly Observatory
TESS provides a unique possibility to observe bright RR Lyrae stars and Cepheids over the entire sky, hence providing information on dynamical phenomena in these stars, such as the Blazhko modulation, period doubling, shock-wave propagation, and additional modes. Ground-based follow-up observations ensure that multi-color and spectroscopic information can help to unravel the atmospheric processes at play. In this talk, I will present some of the first findings on our favorite standard candles, seen by TESS.
topic: Rotation
schedule: Thu, 13:30
(invited)
Jamie Tayar (1,2)
(1) Institute for Astronomy, University of Hawaii (2) Hubble Fellow
With data from Kepler, we have made substantial progress in understanding the evolution of the rotation rates of both the cores and surfaces of low-mass stars. In this talk, I will highlight results which suggest that the cores of stars rotate at similar rates to their surfaces on the main sequence, substantially faster than their surfaces on the giant branch, and then again at similar rates during the core-helium-burning phase. Within this global framework, however, there are still lingering questions about the mechanism for transferring angular momentum in the stellar interior and the location of the radial differential rotation. I will highlight the contributions to these questions that TESS can make by looking at subgiant stars, and discuss preliminary results from a sample of subgiants in the Southern Continuous Viewing Zone.
topic: Rotation
schedule: Thu, 14:00
Sébastien Deheuvels (1); Jérôme Ballot (1); Rafael Garcia (2)
(1) IRAP, Université de Toulouse, CNRS, CNES, UPS, (Toulouse), France; (2) Laboratoire AIM, CEA/DSM-CNRS-Université Paris Diderot, CEA, IRFU, SAp, centre de Saclay, F-91191 Gif-sur-Yvette, France
The detection of rotationally-split mixed modes in the oscillation spectra of Kepler subgiants and red giants has led to the unprecedented opportunity to probe their internal rotation profiles. The cores of red giants were found to spin too slowly compared to current theoretical predictions and it has become clear that an additional, efficient mechanism is transporting angular momentum in these stars. Several candidates have already been proposed, such as internal gravity waves or magnetic fields. The rotation profiles predicted by these different mechanisms differ mainly by the location and the sharpness of the radial gradient of rotation within the star. Asteroseismic observations have unambiguously established that a radial gradient of rotation develops between the core and the envelope of red giants. However, whether this gradient is located in the deep core or within the convective envelope remains unclear. Here, we aim at testing the second hypothesis. For this purpose, we exploit the catalogs of surface rotation rates of Kepler subgiants (Garcia et al. 2014) and red giants (Ceillier et al. 2017). Whenever possible, we extract the rotational splittings of mixed modes and we measure the envelope rotation rate. By combining this measurement to the surface rotation, we place constraints on the amount of differential rotation within the envelope. This will help discriminate between different potential mechanisms of angular momentum transport within red giants.
topic: Rotation
schedule: Thu, 14:15
Timothy Van Reeth (1); Jordan Van Beeck (1); Vincent Prat (2); Joey Mombarg (1); Dominic Bowman (1); Conny Aerts (1,3); Andrew Tkachenko (1); Stéphane Mathis (2,4)
(1) Institute of Astronomy, KU Leuven, Celestijnenlaan 200D, 3001 Leuven, Belgium; (2) AIM, CEA, CNRS, Université Paris-Saclay, Université Paris Diderot, Sorbonne Paris Cité, F-91191 Gif-sur-Yvette, France; (3) Dept. of Astrophysics, IMAPP, Radboud University Nijmegen, 6500 GL, Nijmegen, The Netherlands; (4) LESIA, Observatoire de Paris, PSL University, CNRS, Sorbonne Université, Univ. Paris Diderot, Sorbonne Paris Cité, 5 place JulesJanssen, F-92195 Meudon, France
Angular momentum transport in the deep stellar interior has considerable influence on stellar structure and evolution. However, it is also not well understood, as it is known to be underestimated in stellar evolution models. Both internal gravity waves and magnetic fields are prime candidates to resolve this discrepancy. Gravity-mode pulsations are a promising diagnostic to probe such unexplored physics in the deep stellar interior of main-sequence A/F-type stars. We evaluate the influence of radial differential rotation and magnetic fields on the periods of gravity-mode pulsations. We find that stellar rotation must be strongly differential before it can be detected with gravity-mode period spacing patterns, unless multiple patterns can be compared or the (near-)surface rotation rate can be measured. The effects of magnetic fields on gravity-mode pulsations differ significantly from those of rotation. They depend on the pulsation mode geometry and increase with pulsation period. We characterise these effects for a range of different stellar models, with, e.g., varying mass, age, near-core mixing, (uniform) rotation rate and magnetic field strength. In this talk, we show how both differential rotation and the magnetic field strength in the deep stellar interior may be constrained for a considerable number of main-sequence A/F-type stars, thanks to the high quality and quantity of the data provided by the Kepler and TESS space missions.
topic: Rotation
schedule: Thu, 14:30
Andres Moya (1,2); William J. Chaplin (1,2); Guy R. Davies (1,2); F. Zuccarino (3); A. Miglio (1,2)
(1) School of Physics and Astronomy, University of Birmingham, Edgbaston, Birmingham, B15 2TT, UK; (2) Stellar Astrophysics Centre, Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, DK-8000 Aarhus C, Denmark; (3) Universidad Internacional de Valencia (VIU), E-46021 Valencia, Spain
The estimation of the stellar age is one of the most challenging tasks in stellar characterization. In the literature there are several techniques for stellar aging, being gyrochronology one of the most popular and used. Recently, this technique has been put in doubt reducing its applicability range and claiming for a rotation breaking law change at a certain point of the stellar evolution in Main Sequence. We have used Kepler and K2 asteroseismology legacy to re-evaluate gyrochronology models using the most recent formulations for describing the stellar rotational breaking and machine learning techniques. The resulting models for estimating stellar ages provides accuracies and precisions never reached with the previous gyrochronology relations. With this, we find that 1) this changing in the rotation regime may not be real and 2) gyrochronology can still be useful as an age indicator for FGK star in MS. Nevertheless, the Kepler/K2 asteroseismic legacy sample is imperfect. The current and future TESS data are needed to increase the statistic consistency of these procedures.
topic: Maximizing the Data
schedule: Thu, 15:30
Keaton J. Bell, Saskia Hekker, James S. Kuszlewicz
Max Planck Institute for Solar System Research and the Stellar Astrophysics Centre, Aarhus University
We introduce the fully automated "coefficient of variation" method for detecting solar-like oscillations in photometry from the Kepler, K2, and TESS missions. We exploit the statistical properties of power spectra to sensitively reveal frequency ranges containing stellar oscillation signatures in the presence of granulation backgrounds. These signals cause localized excesses in the coefficient of variation (CV) spectrum---the ratio of the standard deviation to the mean calculated for bins in the power spectrum---a data representation that accentuates the features that an expert would search for in a visual inspection. Bell, Hekker, & Kuszlewicz (2019, MNRAS, 482, 616) showed that this approach successfully recovers detections for 99.4% of solar-like oscillators in the APOKASC sample of red giants that were observed for four years by Kepler, yielding measurements of the frequency of maximum oscillation power, $\nu_{\rm max}$, precise to 2.7%. We demonstrate how this approach generalizes to shorter time series from K2 and TESS, where it is being used to identify large numbers of solar-like oscillators. These will serve as valuable samples for training machine learning classifiers, for which the CV spectrum will also be a valuable input feature.
topic: Maximizing the Data
schedule: Thu, 15:45
Javier Pascual-Granado (1); Sebastiano de Franciscis (1); Antonio García Hernández (2); Juan Carlos Suárez (2); Rafael Garrido (1); Mariel Lares-Martiz (1)
(1) Instituto de Astrofísica de Andalucía - CSIC, Glorieta de la Astronomía s/n, 18008 Granada, Spain; (2) Dept. Física Teórica y del Cosmos, Univ. Granada, Av. Fuente Nueve s/n, 18071 Granada, Spain
We have applied fractal analysis (CGSA) to the frequency extraction of a well-characterized sample of delta Scuti stars. The CGSA algorithm allowed to discriminate the power originated from harmonic components present in the light curves from non-harmonic components by studying their fractal properties. As a consequence, a self-consistent stop criterion was found for frequency analysis methods based on the classical prewhitening technique that is widespread in asteroseismic studies. The new stop criterion is robust since it does not requires any hypothesis about the noise distribution and, more interestingly, it does not rely on the SNR anymore.
Using the CGSA stop criterion we analyze here the light curves of a sample of stars observed by Kepler and TESS satellites. The application of innovative techniques such as this might be crucial to separate the wheat from the chaff and determine the intrinsic frequency spectrum of pulsating stars. At the same time, it can potentially be a rich source of information about the physical mechanisms associated to stellar variability. We explore how the CGSA algorithm can be exploited to understand the different components present in the power spectrum of pulsating stars.
topic: Maximizing the Data
schedule: Thu, 16:00
Enrico Corsaro (1); Jamie Tayar (2)
(1) INAF–Osservatorio Astrofisico di Catania, via S. Sofia 78, 95123 Catania, Italy; (2) Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822, USA
Solar-like and red giant oscillations exhibit a large diversity of features that change as the star evolves, and with different stellar fundamental properties, level of rotation and magnetic activity. The analysis of these oscillations from the stellar power spectra — i.e. identifying each oscillation mode and measuring its frequency, amplitude, and lifetime — is known as peak bagging. It is difficult to efficiently automatize peak bagging because of the complex features and large number of free parameters required to model an oscillation spectrum. However peak bagging is an essential step to exploit the full potential of asteroseismology. In this talk, I will present a new pipeline termed FAMED (Fast and AutoMated pEak bagging with Diamonds) and based on the concept of Bayesian multi-modality (Corsaro 2019) to perform a fast and automated peak bagging analysis of stars from the main sequence to the He-core-burning red giant phase of stellar evolution. I will show how FAMED can efficiently work independently of the properties of the star, the signal to noise and the frequency resolution of the datasets, by presenting results on a benchmark sample of simulated TESS observations (Ball et al. 2018), as well as on real Kepler data of well known stars. In conclusion, I will also show some preliminary results on evolved stars observed within the context of a TESS GI proposal, and for which observations in TESS short cadence modality since September 2018 have been obtained.
topic: Maximizing the Data
schedule: Thu, 16:15
Guy R. Davies, +
University of Birmingham
We present PBjam, a fast, flexible, user-friendly, open source peakbagging tool-box for extracting mode frequencies of solar-like oscillators. PBjam combines cutting-edge data analysis tools and coding techniques, with the vast knowledge gained from the CoRoT and Kepler missions, to help even the most dataphobic astrophysicist peakbag their own stars.
topic: Interactive software demo
schedule: Thu, 16:30 (invited software)
Daniel Foreman-Mackey
Flatiron Institute
In this tutorial, I will demonstrate how Gaussian Processes (GPs) can be used as descriptive and interpretable probabilistic models for stellar variability, including asteroseismic oscillations. We will discuss the relationship between a model for the power spectral density and the GP kernel function, and how fitting oscillations in the time domain enables rigorous treatment of systematic effects and propagation of uncertainty. Finally, I will demonstrate how these models can be efficiently and practically implemented using open source software packages.
topic: 3D Models
schedule: Fri, 9:00
Andreas Christ Sølvsten Jørgensen
Max Planck Institute for Astrophysics, 85748 Garching, Germany
Asteroseismic analyses rely on the predictions of 1D stellar evolution codes that are, however, subject to numerous simplifying assumptions. A prominent example is the incorrect treatment of superadiabatic convection: it leads to a systematic shift in the model frequencies, known as the surface effect, and alters stellar evolution tracks, in the case of stars with convective envelopes. To remedy these drawbacks, we have developed and validated a method to include the mean stratification of 3D simulations of stellar envelopes into our stellar evolution code: we append interpolated 3D envelopes and use these to set the outer boundary conditions of the interior structure at every time-step of the evolution. Using this method, we are able to completely overcome the structural contribution to the surface effect and to reliably mimic the properties of 3D simulations of convection. Furthermore, performing asteroseismic analyses of main-sequence stars, we have investigated the ramifications of the altered evolution on stellar parameter estimates obtained from Bayesian inference. Our results show how realistic multi-dimensional simulations of convection can improve state-of-the-art stellar models and how our novel method can contribute to the interpretation of high-quality data from the Kepler and TESS space missions.
topic: 3D Models
schedule: Fri, 9:15
Yixiao Zhou (1); Martin Asplund (1); Remo Collet (2)
(1) Research School of Astronomy and Astrophysics, Australian National University, Australia; (2) Stellar Astrophysics Centre, Department of Physics and Astronomy, Aarhus University, Denmark
The next decade will witness a rapid development on asteroseismology with the recently launched TESS mission and later PLATO. With more detailed asteroseismic observations available in the near future, it is important to fully understand how oscillations are driven and dissipated in solar-type stars, including quantifying any divergence from the often-used asteroseismic scaling relations for $\nu_{\max}$ and $\Delta \nu$. We have carried out 3D stellar atmosphere simulations of key benchmark stars (Sun, Procyon, Beta Hydri etc) to study this problem from a theoretical perspective. Both mode excitation and damping rates are quantified from first principles, which then allows an estimation of mode amplitude and frequency of maximum power $\nu_{\max}$. We have also combined the 3D surface convection models with MESA 1D stellar evolution models to enable a prediction of the detailed oscillation spectrum and thus $\Delta \nu$. Good agreements between our theoretical results and seismic observations have been achieved for both $\nu_{\max}$ and $\Delta \nu$, which opens the exciting prospect of using such realistic 3D hydrodynamical stellar models to predict the solar-like oscillations across the HR-diagram and test the seismic scaling relations against ab initio predictions for the first time.
topic: Interactive software demo
schedule: Fri, 9:30 (invited software)
Adina D. Feinstein (1); Benjamin T. Montet (1,*); Daniel Foreman-Mackey (2); Megan E. Bedell (2); Nicholas Saunders (3,4); Jacob L. Bean (1); Jessie L. Christiansen (5); Christina Hedges (3, 4); Rodrigo Luger (2); Daniel Scolnic (6); José Vinícius de Miranda Cardoso (7)
(1) Department of Astronomy & Astrophysics, University of Chicago, Chicago, IL; (2) Center for Computational Astrophysics, Flatiron Institute, New York, NY; (3) NASA Ames Research Center, Moffett Field, CA; (4) Bay Area Environmental Research Institute, Petaluma, CA; (5) Caltech/IPAC-NASA Exoplanet Science Institute, Pasadena, CA; (6) Department of Physics, Duke University, Durham, NC; (7) Unidersidade Federal de Campina Grande, Campana Granda, Brazil; (*) Sagan Fellow
During its two year prime mission the Transiting Exoplanet Survey Satellite (TESS) will perform a time-series photometric survey covering over 80% of the sky. This survey comprises observations of 26 24 x 96 degree sectors that are each monitored continuously for approximately 27 days. The main goal of TESS is to find transiting planets around 200,000 pre-selected stars for which fixed aperture photometry is recorded every two minutes. However, TESS is also recording and delivering Full-Frame Images (FFIs) of each detector at a 30 minute cadence. We have developed an open-source software, eleanor, which will provide light curves for 26 million sources in the TESS Input Catalog brighter than I=16 across the sky. eleanor is also available for users to generate their own light curves. In this workshop, I will run through a Jupyter Notebook demonstration on how to use eleanor to produce light curves. eleanor performs background subtraction, aperture and PSF photometry, decorrelation of instrument systematics, and cotrending using principal component analysis. Although the primary goal of eleanor is to find new transiting planets, we include different apertures and software tools to create light curves optimized for a broad range of astrophysics.
topic: Interactive software demo
schedule: Fri, 9:55 (invited software)
Andras Pal
Konkoly Observatory, Research Centre for Astronomy and Earth Sciences, Hungarian Academy of Sciences
Due to the large pixel size and the related confusion of the nearby sources, accurate photometry of TESS full-frame images imply sophisticated methods. In this presentation, we summarize the key points of a photometric pipeline based on differential image processing. Basically, the pipeline has two stages, where the first stage corresponds to the blind analysis of the calibrated and uncropped FFIs while the second stage is a per-target pipeline which processes only a sub-frame centered around the target of interest and has a very small footprint in terms of computing resources. Both of these pipeline stages does not differentiate on the target types, however, some of the parameters of the second stage can be further tuned depending on the target type. Care has been taken in order to merge data from consecutive sectors while keeping both the signal level and the signal amplitude accurately. Some examples are shown from the fields of various TESS disciplines, including pulsating variables, transients and supernovae and simultaneous/quasi-periodic variability on multiple time scales (such as young stellar objects).
topic: Finding and exploring red giants
schedule: Fri, 10:45
Isabel Colman (1,2); Tim Bedding (1,2); Daniel Huber (3); Hans Kjeldsen (2)
(1) Sydney Institute for Astronomy, School of Physics, A28, University of Sydney, NSW 2006, Australia; (2) Stellar Astrophysics Centre, Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, DK-8000 Aarhus C, Denmark; (3) Institute for Astronomy, University of Hawai‘i, 2680 Woodlawn Drive, Honolulu, HI 96822, USA
There is a wealth of information to be found in time series data from the Kepler and TESS missions. To get the most out of these data, we present a method for performing image subtraction photometry on variable targets in clusters and other crowded fields. Image subtraction photometry is distinguished by its ability to highlight variability in time series data, and is particularly useful for targets subject to crowding. We begin with the open cluster NGC 6791, using the Kepler superstamps, long cadence observations which cover the entire cluster in a 200 square pixel field of view. We have produced high quality time series data showcasing stellar oscillations, signals of binarity, and rotational modulation, for both for targeted and untargeted KIC stars in NGC 6791. We compare image subtraction photometry of targeted stars to MAST data, demonstrating that image subtraction does as well as simple aperture photometry for isolated targets, and performs better for crowded targets. We present this method with a view to extend its use to Kepler open cluster NGC 6819, as well as K2 and TESS data.
topic: Finding and exploring red giants
schedule: Fri, 11:00
Anthony Noll; Sébastien Deheuvels
IRAP, Université de Toulouse, CNRS, CNES, UPS, Toulouse, France
The size of convective cores during the main-sequence of low-mass stars is known to have a big impact on their evolution. However, the modeling of its extension is limited by our poor knowledge of several physical processes, such as core overshooting or rotational mixing. Observational constraints are then crucially needed to make progress on this issue. Subgiants show features which make them particularly interesting targets for this purpose. Indeed, the oscillation spectra of these stars contain mixed modes, which probe the fine structure of the core. In particular, they are sensitive to the Brunt-Väisälä frequency profile which keeps an imprint of the size of the main-sequence convective core. However, the very high dependency of mixed modes to the evolution makes the modeling of subgiants challenging, which explains the few number of studies of this kind of star that were led so far. Kepler and TESS data contain an important number of interesting targets which may represent as many potential probes of the core structure. We have developped a new subgiants modeling technique, elaborating on the one proposed by Deheuvels & Michel 2011. Here we present the results of the seismic modeling of several Kepler subgiants and the constraints that we have thus obtained on the core extension. We also show preliminary attempts to apply this method to TESS data.
topic: Finding and exploring red giants
schedule: Fri, 11:15
Nevin N. Weinberg (1); Phil Arras (2)
(1) Massachusetts Institute of Technology, Cambridge, MA; (2) University of Virginia, Charlottesville, VA
Observations by CoRoT and Kepler have shown that the amplitudes of oscillation modes increase dramatically as stars ascend the red giant branch, i.e., as the frequency of maximum power, $\nu_\mathrm{max}$, decreases. Most studies nonetheless assume that the modes are well described by the linearized fluid equations. We investigate to what extent the linear approximation is justified as a function of stellar mass $M$ and $\nu_\mathrm{max}$. We show that that the nonlinearity of mixed modes near $\nu_\mathrm{max}$ increase significantly as a star evolves. The modes are weakly nonlinear for $\nu_\mathrm{max} \lesssim 150 \, \mu\mathrm{Hz}$ and strongly nonlinear for $\nu_\mathrm{max} \lesssim 30 \, \mu\mathrm{Hz}$, with a mild dependence on $M$. A weakly nonlinear mixed mode can excite secondary waves in the stellar core through the parametric instability, resulting in enhanced, but partial, damping of the mode. By contrast, a strongly nonlinear mode breaks as it propagates through the core and is fully damped there. We are carrying out large, coupled mode network calculations to investigate the impact of nonlinear effects on observables such as mode amplitudes and linewidths and to determine whether nonlinear damping can explain why some red giants exhibit dipole modes with unusually small amplitudes, known as depressed modes.
topic: Asteroseismology of planet hosts
schedule: Fri, 11:30
(invited)
Vincent Van Eylen
Princeton
Almost everything we know about exoplanets to date has been inferred indirectly through their host stars, making it crucial to understand stellar properties if one hopes to learn anything at all about the architecture of planetary systems. Asteroseismology, the study of stellar oscillations, provides the current gold standard of stellar characterization. In this talk, I explain how we can use asteroseismology and other techniques can be used to make major leaps forward in our understanding of the formation of small close-in planets, the ones most commonly detected by TESS.
I show what we have learned about the basic properties of planetary systems from previous surveys like Kepler and K2, how these results inform TESS discoveries, and the first results from TESS discoveries. For example, I show what we have learned about orbital eccentricities for single- and multiple-transiting systems and link these findings to planet formation and evolution theories. Furthermore, I show how spectroscopy and asteroseismology have revealed the presence of a so-called "radius valley" in Kepler data, how we interpret this valley as a result of photo-evaporation and the prospect for TESS. Finally, I will highlight in which areas TESS is expected to provide the greatest advancements for combining asteroseismology with exoplanet science, for example by improving our understanding of planet formation and evolution around stars that have evolved off the main sequence.
topic: Asteroseismology of planet hosts
schedule: Fri, 13:30
Tiago Campante (1)
(1) Instituto de Astrofísica e Ciências do Espaço, Universidade do Porto, Porto, Portugal
The Transiting Exoplanet Survey Satellite (TESS) is currently performing a near all-sky survey for planets that transit bright stars. In addition, its excellent photometric precision will enable asteroseismology of solar-type and red-giant stars. In particular, simulations predict that TESS will detect solar-like oscillations in over 100 solar-type and red-giant stars previously known to host planets, the vast majority of which have been discovered using the radial-velocity (RV) method. In this talk, we present the asteroseismic analysis of the evolved known hosts HD 212771 and HD 203949 (an RGB and a red-clump star, respectively), both systems having a long-period planet detected through RVs. This is the first detection of oscillations in any known exoplanet-host star by TESS, further showcasing the mission's potential to conduct asteroseismology of red-giant stars. We estimate the fundamental properties of each star through a grid-based modeling approach that uses global asteroseismic parameters, complementary spectroscopic data and a parallax-based luminosity as input. With a precise asteroseismic mass in hand, we revise the minimum planetary masses quoted in the literature. Finally, we note that HD 212771 was observed by K2 in short-cadence mode during its Campaign 3, which enabled its asteroseismic investigation. Therefore, this provides a unique opportunity to compare, for the first time, the asteroseismic performances of K2 and TESS.
topic: Asteroseismology of planet hosts
schedule: Fri, 13:45
Ashley Chontos (1,2); Daniel Huber (1); Andrew Vanderburg (3,4); Mikkel Lund (5); William J. Chaplin (6,5); Warrick Ball (6)
(1) Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822, USA; (2) NSF Graduate Research Fellow; (3) Department of Astronomy, The University of Texas at Austin, Austin, TX 78712, USA; (4) NASA Sagan Fellow; (5) Stellar Astrophysics Centre, Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, DK-8000, Aarhus C, Denmark ; (6) School of Physics and Astronomy, University of Birmingham, Edgbaston, Birmingham, B15 2TT, UK
Individual studies of exoplanets orbiting asteroseismic stars have allowed for some of the most precisely characterized systems currently known to date. In addition, ensemble studies have yielded unprecedented insights into proposed mechanisms for planet formation and evolution. However, the total population of confirmed planets around seismic stars is still incomplete. Here we present new asteroseismic hosts from Kepler, K2, and TESS based on a systematic analysis of all available data. We analyze recalibrated Kepler short-cadence data to confirm previously known seismic hosts and to identify new asteroseismic host stars that were previously missed. We use overlapping K2 campaigns to present the discovery of new oscillating planet-candidate host stars such as EPIC 211401787, a bright (V = 9.6) solar-like star hosting a super-Earth on an orbital period of ~14 days. Finally, we present results from the first systematic search for asteroseismic hosts in the TESS dataset.
topic: Asteroseismology of planet hosts
schedule: Fri, 14:00
Martin B. Nielsen (1,2) ; Warrick H. Ball (1); William J. Chaplin (1)
(1) University of Birmingham, UK; (2) New York University Abu Dhabi, UAE
The known exoplanet host, λ² Fornacis, was observed by TESS during Sectors 2 and 3, and even with such limited amounts of data oscillations have been detected. λ² Fornacis is a sub-giant which is known to host a Neptune-like planet in a close 17d orbit. However, the fundamental properties of the star have so far remained uncertain, with multiple studies providing a large range of values. Here we present one of the first asteroseismic analyses of an exoplanet host observed by TESS, providing tight constraints on the characteristics of λ² Fornacis, and in turn also the properties of the orbiting planet.
topic: Asteroseismology of planet hosts
schedule: Fri, 14:15
Charlotte Gehan
LESIA - Paris Observatory
Red giants represent an ideal laboratory to study the physical mechanisms governing deep stellar interiors as their oscillation spectra exhibit mixed-modes. Their dipole mixed-modes split by rotation are well separated since rotational splittings are much larger than mode linewidths. Mixed-modes thus offer the opportunity to obtain accurate measurements of the stellar inclination, that are much more difficult for stars on the main-sequence that do not exhibit mixed-modes. Information on stellar inclinations are of prime importance to reach a better understanding of the formation and dynamics of transiting exoplanetary systems, by constraining the angle between the stellar spin axis and the planetary orbit axis, namely the obliquity. A few hundreds of exoplanets are already known to orbit red giants and subgiants presenting mixed-modes. The detection of a much larger number of planets around evolved stars is crucial to constrain theoretical models of planet engulfment by the expanding host star and to understand what is the effect of stellar evolution on the orbital and physical properties of planetary systems. In this context, measuring stellar inclination angles on a large-scale for evolved stars is a major stepping stone in the understanding of planetary formation, evolution and death. I will present results on stellar inclination measurements for more than a thousand stars on the red giant branch that turn out to be highly valuable for the exoplanetary community.
topic: Closing
schedule: Fri, 14:30
(invited)
Sara Seager
Massachusetts Institute of Technology
TESS will have completed the first year of its prime mission by the time of the workshop, mapping most of the southern ecliptic hemisphere. Although the TESS primary science goal is to discover small exoplanets whose masses can be measured with ground-based telescopes, the large 24x96 degree field of view and continuous 30-min cadence for each 27 day sector opens up a wide range of astronomy. The value of TESS data can be increased when combined with recent GAIA data, or with near simultaneous ground or space-based multi-wavelength observations. I will present recent science highlights from the TESS first year in space and prospects for the future. With TESS capable of lasting for a decade or more, and plans to decrease the observing cadence to 10 minutes, there is much to look forward to.
poster number: 25
A. Derekas (1,2,3) ; S. J. Murphy (4,5) ; G. Dálya (6) ; R. Szabo (2,17) ; T. Borkovits (7,2) ; A. Bókon (8); H. Lehmann (9) ; K. Kinemuchi (10) ; J. Southworth (11) ; S. Bloemen (12) ; B. Csak (2,1) ; H. Isaacson (13); J. Kovacs (1,3) ; A. Shporer (14) ; Gy. M. Szabo (1,3) ; A. O. Thygesen (15) ; Sz. Meszaros (1,3,16);
(1) ELTE Eötvös Loránd University, Gothard Astrophysical Observatory, Szombathely, Hungary; (2) Konkoly Observatory, Research Centre for Astronomy and Earth Sciences, Hungarian Academy of Sciences, H-1121 Budapest, Konkoly Thege Miklós út 15-17, Hungary; (3) MTA-ELTE Exoplanet Research Group, 9700 Szombathely, Szent Imre h. u. 112, Hungary; (4) Sydney Institute for Astronomy, School of Physics, The University of Sydney, NSW 2006, Australia; (5) Stellar Astrophysics Centre, Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, DK-8000 Aarhus C, Denmark; (6) Institute of Physics, Eötvös University, 1117 Budapest, Hungary; (7) Baja Astronomical Observatory of Szeged University, H-6500 Baja, Szegedi út, Kt. 766, Hungary; (8) Department of Experimental Physics, University of Szeged, H-6720 Szeged, Dóm tér 9, Hungary; (9) Thüringer Landessternwarte Tautenburg, Karl-Schwarzschild-Observatorium, 07778 Tautenburg, Germany; (10) Apache Point Observatory, Sunspot NM 88349, USA; (11) Astrophysics Group, Keele University Newcastle-under-Lyme, ST5 5BG, UK; (12) Department of Astrophysics/IMAPP, Radboud University Nijmegen, P.O. Box 9010, NL-6500 GL Nijmegen, Netherlands; (13) Department of Astronomy, University of California at Berkeley, Berkeley, CA 94720-3411, USA; (14) Kavli Institute for Astrophysics and Space Research, M.I.T., Cambridge, MA 02139, USA; (15) California Institute of Technology, 1200 E. California Boulevard, Pasadena, CA 91125, USA; (16) Premium Postdoctoral Fellow of the Hungarian Academy of Sciences; (17) MTA CSFK Lendület Near-Field Cosmology Research Group
We present the analysis of the hybrid delta Sct/gamma Dor pulsator KIC5709664. We used Kepler data and applied the frequency modulation (FM) method and found that KIC5709664 was a good candidate being in binary system. We determined the orbital parameters and took spectroscopic measurements to confirm unambiguously the binary nature with radial velocities. We combined a radial velocity and phase modulation approach to determine the orbital parameters as accurately as possible. We determined that the hybrid pulsator is in an eccentric binary system with an orbital period of ̃95 d and an eccentricity of 0.55. The measured mass ratio is 0.67. We analysed the pulsation content and extracted 38 frequencies with amplitudes greater than 0.02 mmag. At low frequencies, we found broad power excesses which are likely attributed to spots on the rotating surface of the lower mass component. We inferred rotation periods of 0.56 and 2.53 d for the primary and secondary, respectively.
poster number: 3
A. Tkachenko (1); J. Kuszlewicz (2); K. Bell (2); D. Armstrong (3); M. Hon (4); R. Kgoadi (5); L. Bugnet (6); R. Handberg (7); M. N. Lund (7); T'DA collaboration
(1) Institute of Astronomy, KU Leuven, Leuven, Belgium; (2) Max Planck Institute for Solar System Research, Goettingen, Germany; (3) Department of Physics, University of Warwick, Coventry, UK; (4) School of Physics, The University of New South Wales, Sydney, Australia; (5) College of Science and Engineering, James Cook University, Townsville, Australia; (6) IRFU, CEA, Université Paris-Saclay, France; (7) Stellar Astrophysics Centre (SAC), Department of Physics and Astronomy, Aarhus University, Aarhus, Denmark
TESS will deliver tens of millions of high-precision light curves of stars across the entire sky during the 2 years of its nominal mission. Lessons learned from the recently retired Kepler mission allow us to say that the vast majority of targets observed by TESS will be in- or/and extrinsically variable over time. Given the total amount of light curves that will become available, (astro)physical information encoded in stellar variability, and the importance of ensemble studies, it is highly beneficial to classify stars according to the type of their variability and to do it in a highly automated and homogeneous approach. In this contribution, we will present the concept of the T’DA classification pipeline whose task is to sort out stars in the first place as well as to provide a feedback to the TASOC Photometry pipeline as to how to improve upon correction of light curves for non-astrophysical signals. This classification is realised by means of supervised and unsupervised machine learning algorithms, and comes in two subsequent stages: 1) general classification (g-mode pulsators, p-mode pulsators, eclipsing/transiting objects, classical pulsators, etc.), and 2) detailed classification (gamma Dor vs. SPB stars, RR Lyrs vs. Cepheids, etc.).
poster number: 32
Alexandra E. L. Thomas (1,2); Guy R. Davies (1,2); William J. Chaplin (1,2)
(1) School of Physics and Astronomy, University of Birmingham, UK; (2) Stellar Astrophysics Centre, Department of Physics and Astronomy, Aarhus University, Denmark
Asteroseismic power spectra contain numerous features (granulation, modes, spacings, patterns, etc.) that in principle can be explained by a small number of fundamental properties (mass, metallicity, age, Helium). We present a data-driven approach for determining fundamental stellar properties directly from asteroseismic power spectra. We have built a Bayesian Neural Network to model red giant power spectra in a multistep process by searching a reduced parameter space comprising the quantities: Teff, metallicity, mass and numax. Importantly, our method properly accounts for uncertainties in input properties, observed properties, and in the map from inputs to outputs. We present the capability of this process along with plans for the next stage.
poster number: 29
Attila Bódi (1,2); Emese Plachy (1,2); Pál Szabó (1,2); László Molnár (1,2)
(1) Konkoly Observatory, Research Centre for Astronomy and Earth Sciences, Konkoly Thege Miklos ut 15-17, H-1121 Budapest, Hungary; (2) MTA CSFK Lendület Near-Field Cosmology Research Group, Konkoly Thege Miklos ut 15-17, H-1121 Budapest, Hungary
The K2 and the TESS missions provide an unique opportunity to investigate the phenomenon of the Blazhko effect in great detail. We present the analysis of nearly two hundred Blazhko stars that represent the largest sample of modulated RR Lyrae stars investigated with space-based photometry so far. We focus on the relation between the modulation of the pulsation phase and the pulsation amplitude, as well as the coexistence of the Blazhko effect with the nonlinear phenomenon called period doubling. Given the limited length of observations, we were able to determine only relatively short modulation periods accurately. Nevertheless, we show that the pulsation amplitude and phase changes are not necessarily correlated and their relation can be rather complex.
poster number: 21
Camilla C. Borre ; Victoria Antoci
Stellar Astrophysics Centre, Aarhus University, Ny Munkegade 120, DK-8000 Aarhus C, Denmark
$\gamma$ Dor stars are early F- to A-type stars and are slightly more massive than the sun. This makes them the closets relatives to solar-like stars in mass and evolution and thereby, a stepping stone in understanding stellar structure and evolution. $\gamma$ Dor stars display g (gravity) mode and r (Rossby) mode oscillations making it possible to probe their interiors. With Kepler many stars were found to have period spacing patterns in the g and r modes, which allows us to measure rotation and chemical gradients in the stars. There are, however, still many open questions e.g. related to their excitation mechanism. Here we show first results of our ensemble analysis of Kepler $\gamma$ Dors. We have examined amplitude, frequency and combination frequency distributions and how these relate to stellar parameters such as temperature, age and metallicity. One aim of this work is to get an insight into how the class of $\gamma$ Dor stars are spread over e.g. the HR-diagram or what percentage of stars oscillate in specific ways. Our findings are based on Kepler data and will be used to analyse TESS $\gamma$ Dors.
poster number: 22
D.L. Holdsworth (1); H. Saio (2); D.W. Kurtz (1)
(1) Jeremiah Horrocks Institute, University of Central Lancashire, Preston PR1 2HE, UK; (2) Astronomical Institute, School of Science, Tohoku University, Sendai 980-8578, Japan
We present a multi-instrument analysis of the rapidly oscillating Ap (roAp) star HD 42659. We have obtained new $B$ photometric data for this star and use this, in conjunction with TESS observations, to analyse the high-frequency pulsation in detail not presented before. Although we find a triplet which is split by the rotation frequency of the star, we are unable to confirm whether the pulsation mode is a dipole or a distorted quadrupole mode. We utilise 27 high-resolution ($R\sim65\,000$), high signal-to-noise ($\sim200$) spectra to provide new orbital parameters for this, the only known roAp star to be in a short period binary. We find the system to be more eccentric than previously though, and suggest the companion is of late-F to mid-G type. We find that the average pulsation mode amplitude, as measured by TESS, shows a slight trend to lower amplitude as the system approaches periastron passage, leading us to conclude that the companion does have an affect on the pulsation in this roAp star.
poster number: 23
E. Brunsden (1,2); K.R. Pollard (2)
(1) Department of Physics, University of York, Heslington, York, YO10 5DD, UK; (2) School of Physical and Chemical Sciences, University of Canterbury, Private Bag 4800, Christchurch, New Zealand
Hybrid stars of the $\gamma$ Doradus and $\delta$ Scuti pulsation types have great potential for asteroseismic analysis to explore their interior structure. To achieve this, mode identifications of pulsational frequencies observed in the stars must be made. Both high-precision photometry and high-resolution spectroscopy can identify frequencies and modes, but do they agree? Here we examine the only $\gamma$ Doradus and $\delta$ Scuti hybrid star currently with sufficient spectroscopic observations to address this question. HD\,49434 is one of the most observed hybrid stars with more than 1300 spectra and photometry from the ground, CoRoT and now TESS. The results show almost no consistency between the frequencies found using the two techniques. Are we messing up our analysis? Are we missing some physics? Is this star even a hybrid after all? We present early work to answer these questions.
poster number: 17
Emil Knudstrup; Mikkel N. Lund; Frank Grundahl
Stellar Astrophysics Centre, Aarhus University; Stellar Astrophysics Centre, Aarhus University; Stellar Astrophysics Centre, Aarhus University
Precise determination of fundamental stellar parameters, such as mass, radius, and age, for single stars is possible using asteroseismology. Although precise, these asteroseismically determined parameters are not necessarily accurate and are typically obtained from scaling relations of average seismic parameters. It is therefore essential that the asteroseismic parameters are tested against model-independent counterparts. This can be achieved using detached eclipsing binaries (dEBs) for which it is possible to obtain accurate masses and radii of the components. For dEBs in star clusters it is then possible to extrapolate the measurements to the position of the oscillating member of the cluster. We aim to do this for the open cluster NGC~2506 for which we have already determined masses and radii for three pairs of dEBs (Knudstrup et al. in prep.) spanning masses from $0.7$~M$_\odot$ to $1.6$~M$_\odot$. NGC~2506 was observed by TESS (Ricker et al. 2014) in the full-frame images (FFIs) during sector 7 and should allow us to detect oscillations in sub- and red giant branch stars. Given the large pixel size of TESS detecting oscillations in crowded clusters is a difficult endeavor, but by making use of Gaia (Gaia Collaboration et al. 2016) and well-calibrated Strömgren photometry as well as spectroscopic measurements of the cluster we try to overcome this challenge.
poster number: 7
Erich Hartig (1,2), Kenneth H. Hinkle (3), Thomas Lebzelter (1)
(1) University of Vienna, Department of Astrophysics, Tuerkenschanzstrasse 17, A-1180 Vienna, Austria; (2) erich.hartig@univie.ac.at ; (3) National Optical Astronomy Observatories, P.O. Box 26732, Tucson, AZ 85726 USA
The Gaia Data Release 2 (Gaia DR 2) provided details about 550.737 stars based on 22 months of observations from 2014-07-25 to 2016-05-23, 151 761 of them are long-period variables (LPV) and published in Mowlavi et al. 2018 1). The All-Sky LPV Catalogue from the All-Sky Automated Survey for Supernovae (ASAS-SN) V-band survey (Jayasinghe et al. 2018) 2) analyzed ~421.000 variable stars of the VSX Catalog. The Kepler K2 SFF data provided high quality details but are restricted by the relatively short time span covered of roughly 90 days. The three data sets have been obtained with some overlap in time, and thus offer a direct comparison of the light curves obtained by the different missions/projects. We selected a set of LPVs from our own Kepler K2 program 3) for this study. ASAS observations starting from 1997 were included to explore any long-time trends.
In this poster we discuss a selection of adjustment methods for the zero points of the various data sets and the problems encountered when looking for the most appropriate solution. We test the influence of the zero point settings on the calculated periods of the combined datasets, exploring also the case of multiple periods. First results for a few showcases are presented.
Ref.: 1) N. Mowlavi, I. Lecoeur-Taibi, T. Lebzelter, + Gaia DR 2: The first Gaia cat LPVs, A&A, Vol 618, id. A58pp. 3) E. Hartig, K. Hinkle, T. Lebzelter, 2017, Kepler-K2: A Search for Very Red Vars, TASC2 & KASC9 Workshop, EPJ Web of Conf., V160, 01008
poster number: 33
Filipe Pereira (1,2); Tiago L. Campante (1,2); Margarida S. Cunha (1,2); João P. Faria (1); Nuno C. Santos (1,2); Susana C. C. Barros (1,2); Olivier Demangeon (1); James S. Kuszlewicz (3,4); Enrico Corsaro (5)
(1) Instituto de Astrofísica e Ciências do Espaço, Universidade do Porto, CAUP, Rua das Estrelas, PT4150-762 Porto, Portugal; (2) Departamento de Física e Astronomia, Faculdade de Ciências, Universidade do Porto, Rua do Campo Alegre, PT4169-007 Porto, Portugal; (3) Max Planck Institute for Solar System Research, D-37077 Göttingen, Germany; (4) Stellar Astrophysics Centre (SAC), Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, DK-8000 Aarhus C, Denmark; (5) INAF – Osservatorio Astrofisico di Catania, via S. Sofia 78, 95123 Catania, Italy
The search for transiting planets in photometric time series is often hindered by the presence of signals associated with stellar variability, namely stellar oscillations and granulation. Whilst for main sequence planet hosts the stellar signals usually average out when phase-folding the light curve, for evolved planet hosts, stellar granulation has larger amplitudes and its timescales are similar to the transit duration of close-in giant planets. This suggests a need to model these signals alongside the transit signal in order to correctly characterize the planet. In this presentation we show a method that captures both the stellar signals (through Gaussian Process regression) and planetary transits in the same model when fitting the data. To show the applicability of the method, we use it on TESS simulated light curves with injected transits and show that it recovers the same stellar and planetary parameters used to generate the data. We also apply the method to known Kepler evolved star hosts, to check if the results agree with the literature, and to known hosts recently observed by TESS.
poster number: 6
Gerald Handler (1); Jim Fuller (2); Donald W. Kurtz (3); Saul A. Rappaport (4); Hideyuki Saio (5); Sowgata Chowdhury (1); Paulina Sowicka (1); Robert Gagliano (6); Tom L. Jacobs (7)
(1) Nicolaus Copernicus Astronomical Center, Polish Academy of Sciences, ul. Bartycka 18, 00-716, Warszawa, Poland; (2) Division of Physics, Mathematics and Astronomy, California Institute of Technology, Pasadena, CA 91125, USA; (3) Jeremiah Horrocks Institute, University of Central Lancashire, Preston PR1 2HE, UK; (4) Department of Physics, and Kavli Institute for Astrophysics and Space Research, M.I.T., Cambridge, MA 02139, USA; (5) Astronomical Institute, Graduate School of Science, Tohoku University, Sendai 980-8578, Japan; (6) Planet Hunters; (7) Amateur Astronomer, 12812 SE 69th Place Bellevue, WA 98006
We have discovered tidally trapped pulsations in the ellipsoidal variable HD 74423, containing a $\delta$-Scuti pulsator in a 1.6 day orbit with a low-mass companion star. The pulsating primary star (nearly) fills its Roche lobe, and the pulsations have about eight times larger amplitude in the hemisphere that faces the (so far undetected) secondary star. We interpret this as a dipole oscillation whose pulsation axis has been tilted into the orbital plane and points toward the secondary star. This is the first time such a phenomenon has been observed. Our results also suggest that this is the first evolved EL CVn and R CMa-type system; mass transfer from the previous secondary star to the former primary star is about to set on. We present a crude physical model demonstrating how stellar oscillations can be tidally trapped and amplified near the star's L1 point.
poster number: 15
JJ Hermes; Huyongqing Chen; Kera Regan-Byrne
Boston University
We explore the ensemble of oscillation periods observed (both in the original mission and K2) of the more than 70 unique DA (hydrogen-atmosphere) pulsating white dwarfs observed in short cadence by the Kepler space telescope.
poster number: 9
James S. Kuszlewicz (1,2)
(1) Max-Planck-Insitute for Solar System Research, Justus-von-Liebig-Weg 3, 37077 Göttingen, Germany; (2) Stellar Astrophysics Centre (SAC), Department of Physics and Astronomy, Aarhus University, Ny Mukegade 120, DK-8000 Aarhus C, Denmark
The stellar inclination angle—the angle between the rotation axis of a star and our line of sight—provides valuable information in many different areas, from the characterisation of the geometry of exoplanetary and eclipsing binary systems, to the formation and evolution of those systems. We propose a method based on asteroseismology and a Bayesian hierarchical scheme for extracting the inclination angle of a single star. This hierarchical method therefore provides a means to both accurately and robustly extract inclination angles from red giant stars. We successfully apply this technique to an artificial dataset with a underlying isotropic inclination angle distribution to verify the method. We also apply this technique to 123 red giant stars observed with Kepler. We also show the need for a selection function to account for possible population-level biases, that are not present in individual star-by-star cases, in order to extend the hierarchical method towards inferring underlying population inclination angle distributions.
poster number: 10
Jennifer Johnson
Ohio State University
The multi-object, wide-field, near-IR APOGEE spectrographs have been observing red giants in the North and South TESS CVZs. These spectra provide metallicity, gravity, temperature, evolutionary state, and mass information that inform predictions for what populations will be seen when frequency power spectra are studied.
poster number: 16
Joseph Guidry (1); Zachary Vanderbosch (1); JJ Hermes (2); Michael Montgomery (1)
(1) Department of Astronomy, The University of Texas at Austin; (2) Department of Astronomy, Boston University
Recently, thanks to analysis from Kepler and K2 mission data, a new phenomenon has been observed in a select population of pulsating hydrogen atmosphere white dwarfs (or ZZ Cetis): outbursts. These outbursting white dwarfs undergo outbursts that cause their mean flux to irregularly spike from 2% up to 15% over the course of 4 to 25 hours. Two of these outbursting white dwarfs were observed for more than 80 days by K2 during its Campaigns 16 and 17: EPIC 211629697 and EPIC 211968416. Simultaneously, the Panoramic Survey Telescope and Rapid Response System, or Pan-STARRS (PS1), observed the same field of view in four different color filters (g, r, i, and z) with 30 second integrations. Using the K2 light curves we identified 12 frames out of 54 PS1 images that are situated within or near an outburst for EPIC 211629697, as well as 20 of 59 for EPIC 211968416. We report aperture photometry results on these PS1 frames and present an exploration of these data for color information to search for changes in surface temperature for the frames in outburst relative to phases of quiescent pulsations.
poster number: 26
K.R. Pollard (1); E.J. Brunsden (2); R. Dorsey (1); F. Gunn (1)
(1) University of Canterbury, Christchurch, New Zealand; (2) University of York, York, United Kingdom
We have obtained simultaneous and contemporaneous high resolution echelle spectra of southern hemisphere TESS $\gamma$~Dor targets from the University of Canterbury Mt John Observatory and HERCULES spectrograph. In this paper we present our identification of the pulsational frequencies and spectroscopic mode identifications of selected targets from our campaign.
poster number: 31
Keaton J. Bell
Max Planck Institute for Solar System Research and the Stellar Astrophysics Centre, Aarhus University
Python has recently become the preferred language for astronomical research. The development and availability of Python packages for common research tasks has accelerated the analysis of an increasing volume of survey data. The lightkurve package has especially lowered the barrier to working with time series data from Kepler and TESS. However, a satisfactory, user-friendly Python solution for common next steps of variable star analysis has not been available. This has resulted in stilted workflows, where astronomers often write out the data that they’ve processed in Python, do a frequency analysis with legacy code such as Period04, then read those results back into Python for further analysis and visualization. To help streamline modern variable star research, I introduce Pyriod, a Python package for astronomical frequency analysis. While still under development, this code already provides the most useful features of Period04, including an intuitive GUI that works within Jupyter Notebooks. Code and examples are available on GitHub.
poster number: 28
Khalack V., Kobzar O.
Département de Physique et d'Astronomie, Université de Moncton, Moncton, N.B., Canada E1A 3E9
The TESS space telescope will perform photometric observation of the whole celestial sphere and provide data for more than $10^5$ relatively bright stars. To succeed with the analysis of this extensive amount of data, we have created a high-performance autonomous computing procedure that carries out periodic analysis of the obtained light curves, detects stellar pulsations and selects stars with desired type of photometric variability. We aim to select and study a sample of slowly rotating (P > 2d) magnetic CP (mCP) stars, but the procedure is suitable to select a sample of stars with any given type of photometric variability that can be registered with the TESS. This procedure will help validate the stellar classification of the observed objects, as they appear in existing catalogues of variable stars. It will also help to identify slowly rotating mCP stars, derive their rotational periods and study stellar pulsations.
poster number: 14
Klara Gynther Karlsmose
Stellar Astrophysics Centre, Department of Physics and Astronomy, Aarhus University, Denmark
Three-dimensional hydrodynamic simulations provide the most realistic approach to the modeling of stellar surface inhomogeneities. So far, numerical simulations computed using the Stagger code has relied on pre-tabulated equation of state values. In a desire to test the effects of different chemical compositions on stellar model atmospheres, another equation of state by Irwin (2012) is being tested with the purpose of implementing it in the Stagger code. The focus is to investigate the evolutionary effects of a change in the helium abundance.
poster number: 20
Lares-Martiz, M., Garrido, R., Pascual-Granado, J.
(1) Institute of Astrophysics of Andalusia , Glorieta de la Astronomía s/n, 18008, Granada, Spain.
Non-linear interactions of the main pulsation frequencies in some intermediate-mass pulsating stars results in peaks in their power spectra which can be considered as spurious as far as they don't give us information about the spherical harmonic.
The poster presents a new methodology to remove these peaks, called combinations frequencies, from the power spectra. This methodology is based on an unbiased estimation of the non-linear solution that guarantees uncorrelated residuals.
Application of the method to HADS and LADS previously studied by the community, provides new keys to understand these non-linear effects. When applied to monoperiodic Cepheid stars, the fundamental period is compatible with that obtained from the classical O-C procedure, which is known to be the more precise method to calculate the period of a monoperiodic signal.
poster number: 36
László Molnár (1); András Pál (1,2); Csaba Kiss (1); Róbert Szakáts (1); Gyula M. Szabó (3,1); Krisztián Sárneczky (1); Gábor Marton (1); Róbert Szabó (1); József Vinkó (1); Csilla Kalup (1,2); Anikó Farkas-Takács (1); László Kiss (1)
(1) Konkoly Observatory, MTA CSFK, Budapest, Hungary; (2) Department of Astronomy, Eötvös University, Budapest, Hungary; (3) ELTE Gothard Astrophysical Observatory, Szombathely, Hungary
Observing in or near the Ecliptic plane can be a nuisance, with asteroids, planets and moons polluting stellar photometry. However, continuous observations can be exploited for planetary science as well. Here we show how to spot moving targets contaminating your source, and summarize how can we utilize the exoplanet hunter missions to learn more about one particular solar system: ours.
poster number: 37
Maria Pia Di Mauro (1); Luca Giovannelli(2); Francesco Berrilli (2)
(1)INAF-IAPS Roma, Italy; (2) University of Tor Vergata, Roma, Italy
We present a new approach to characterize habitability of exoplanets making use of Asteroseismology and exploring the possible factors influencing exoplanetary climate. The objective is achieved by fulfilling the following tasks: 1. Asteroseismology of solar-type stars by using Kepler or TESS data for determination of high-precision parameters of stars with detected rocky exoplanets 2. Characterization of habitability by studying the planet-star interaction, modelling conditions of exoplanetary climate taking into account stellar activity and extreme space weather factors.
poster number: 11
Maria Pia Di Mauro (1); Frank P. Pijpers (2)
(1) INAF-IAPS Roma Italy; (2)Centraal Bureau voor de Statistiek, The Hague, Netherlands
The measurement of the total angular momentum of stars, a parameter of high astrophysical interest, can be determined with reasonable accuracy by means of asteroseismology. Here we estimate the total angular momentum of the red-giant star KIC4448777 observed by Kepler during the first four consecutive years of operation, by adopting asteroseismic inversion technique developed by Pijpers (2003).
poster number: 1
Mikkel N. Lund (1); Rasmus Handberg (1); Derek Buzasi (2); Lindsey Carboneau (2); Oliver J. Hall (3,1); Filipe Pereira (4,5); T'DA Collaboration
(1) Stellar Astrophysics Centre, Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, DK-8000 Aarhus C, Denmark; (2) Department of Chemistry and Physics, Florida Gulf Coast University,; 10501 FGCU Blvd. S., Fort Myers, FL 33965 USA; (3) School of Physics and Astronomy, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK; (4) Instituto de Astrof´ısica e Ciˆencias do Espa¸co, Universidade do Porto, CAUP, Rua das Estrelas, 4150-762 Porto, Portugal; (5) Departamento de F´ısica e Astronomia, Faculdade de Ciˆencias da Universidade do Porto, Rua do Campo Alegre, s/n, PT4169-007; Porto, Portugal
With data from the Transiting Exoplanet Survey Satellite (TESS) the seismic community is faced with a new set of challenges concerning the preparation of data. The TESS Asteroseismic Science Operations Center (TASOC) is tasked with delivering light curves ready for asteroseismic analysis to the TESS Asteroseismic Science Community (TASC) for each target observed by TESS.
Following the photometric extraction of targets observed in the TESS full-frame images, the next step is to correct for systematic signals in the light curves while preseving the intrinsit stellar variability. This is achieved using a custom-built, Open Source, pipeline produced within the TASC community by the coordinated activity "TESS Data for Asteroseismology" (T'DA).
For TESS sectors 1 and 2 the first full release resulted in over 1.7 million light curves, which have been released to the community via the TASOC and MAST websites, and many more are to come.
poster number: 35
Nada Jevtic (1); Peter Stine (1)
(1) Bloomsburg University of PA, 400 E 2nd St, Bloomsbburg, PA 17815, USA
Average mutual information (AMI), a tool borrowed from information theory, is more general and is not limited to linear dependence like the correlation coefficient. On the one hand, it can be used in light curve analysis to preview the amplitude spectrum and guide nonlinear noise reduction. On the other hand, it and its associated Shannon entropy, can be used to estimate asteroseismic information retention in PDC-SAP light curves. We use KIC 10119517 long cadence data to illustrate the former, and TESS 3905338 long cadence data to discuss the latter.
poster number: 12
Nathalie Themeßl (1,2)
(1) Max Planck Institute for Solar System Research, Justus-von-Liebig-Weg 3, 37077 Göttingen, Germany; (2) Stellar Astrophysics Centre, Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, 8000 Aarhus C, Denmark
Asteroseismology has been proposed as a method to identify non-eclipsing binary systems in cases where more than one component of the system shows solar-like oscillations. Based on high-precision photometric data obtained by the $Kepler$ mission, we analyze about 30 rare power density spectra of red-giant stars that show two sets of solar-like oscillations. Complementary to the asteroseismic study, we use spectroscopic effective temperatures and metallicities as well as ground-based BVI photometry and $Gaia$ DR2 parallaxes to investigate if the pairs of stars have similar stellar properties. A mass ratio close to 1, similar ages, and distances can be an indication that the stars are physically bound in a binary system. For each pair of stars, we provide probabilities for it being a binary system or rather visual double stars. This study supports the search for candidate systems that are suitable for further binary investigations.
poster number: 4
Nicholas Saunders (1, 2); Oliver J. Hall (3); Christina Hedges (1, 2); Geert Barentsen (1, 2); Michael Gully-Santiago (1, 2); Ann-Marie Cody (1, 2); Jessie Dotson (4)
(1) Kepler/K2 Guest Observer Office; (2) Bay Area Environmental Research Institute; (3) University of Birmingham; (4) NASA Ames Research Center
In addition to revolutionizing the study of exoplanets, Kepler, K2, and TESS data are providing a wealth of asteroseismology discoveries. Software tools such as Lightkurve and Scope lower the bar for astronomers to conduct asteroseismic analyses with space telescope data. We describe new asteroseismic features which have recently been added to the Lightkurve open-source Python package and vetted by members of the community. Additionally, we describe Scope, a Python tool to simulate CCD observations and characterize noise and potential biases introduced by instrumental systematics. We show examples of how Scope can be used to test recovery and characterization of stellar signals in Kepler and TESS light curves.
poster number: 27
Oliver J. Hall (1, 2), Guy R. Davies (1, 2), Martin B. Nielsen (1, 2)
1) School of Physics and Astronomy, University of Birmingham, Edgbaston, Birmingham, B15 2TT, UK; ; 2) Stellar Astrophysics Centre, Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, 8000 Aarhus C, Denmark
Gyrochronology describes how a star’s rotation slows down with age as a function of its colour, and can be used to determine ages of stars for which this would otherwise be difficult. However the form of this relation is still unclear, as we are unsure how the slowing of rotation changes for older stars, and lack a full physical understanding of the process. Typically gyrochronology is calibrated through isochrone ages of young clusters and rotation from spot modulation, but these techniques can be less reliable for field stars and stars that are old and less active, limiting our ability to properly calibrate gyrochronology.
Asteroseismology solves these problems by measuring stellar rotation from p-mode frequency splittings and age through comparison to stellar models. In this work, we obtain new periods of rotation for 95 stars in the Kepler LEGACY (Lund et al. 2017; Silva Aguirre et al. 2017) and Kages (Silva Aguirre 2015; Davies et al. 2016) samples, representing some of the highest signal-to-noise main sequence field stars observed by Kepler, and span up to 13 Gyr in age. In this poster, we compare our new rotation periods with established asteroseismic ages and Gaia BP-RP colours to calibrate the gyrochonology relation for field stars, as well as modelling its dependence on mass and metallicity.
poster number: 30
Pal Szabo (1,2); Emese Plachy (1,2); Attila Bodi (1,2); Laszlo Molnar (1,2)
(1) Konkoly Observatory, Research Centre for Astronomy and Earth Sciences, Konkoly Thege Miklos ut 15-17, H-1121 Budapest, Hungary; (2) MTA CSFK Lendület Near-Field Cosmology Research Group, Konkoly Thege Miklos ut 15-17, H-1121 Budapest, Hungary
Light curves for RR Lyrae stars can be difficult to obtain properly in the K2 mission due to the similarities of timescales of the observed physical phenomena and the appearing instrumental signals in the data. We developed a new photometric method, a key element of which is to extend the aperture to an optimal size to compensate for the motion of the telescope and to collect all available flux from the star before applying further corrections. We found that the EAP (Extended Aperture Photometry) is more likely to provide useful light curves for the faintest targets than other existing pipelines. The greatest challenge in EAP is that apertures must be determined individually. We used four hundred manually created apertures from the early campaigns to work out an automatized pixel selection mechanism that can be applied in later campaigns. We then used this automated EAP pipeline on the nearly two thousand RR Lyrae targets observed in the later campaigns of the K2 mission. Here we present the description of our pipeline and compare our results to other photometry solutions.
poster number: 2
R. Handberg (1); M. N. Lund (1); J. S. Hansen (1); T. R. White (2,1); B. Pope (3); O. J. Hall (4,1); and the T'DA collaboration
(1) Stellar Astrophysics Centre, Aarhus University, Denmark.; (2) Research School of Astronomy and Astrophysics, Mount Stromlo Observatory, The Australian National University, Australia.; (3) Center for Cosmology and Particle Physics, Department of Physics, New York University, USA.; (4) School of Physics and Astronomy, University of Birmingham, UK.
With data from the Transiting Exoplanet Survey Satellite (TESS) the seismic community is faced with a new set of challenges concerning the preparation of data. The TESS Asteroseismic Science Operations Center (TASOC) is tasked with delivering light curves ready for asteroseismic analysis to the TESS Asteroseismic Science Community (TASC) for each target observed by TESS.
The first step in this process is extraction of light curves for every single target down to TESS magnitude of 15, that falls on the TESS full-frame images or target pixel files. This is achieved using a custom-built, Open Source, pipeline produced within the TASC community by the coordinated activity "TESS Data for Asteroseismology" (T'DA).
For TESS sectors 1 and 2 the first full release resulted in over 1.7 million light curves, which have been released to the community via the TASOC and MAST websites, and many more are to come.
poster number: 13
Regner Trampedach (1), Werner Däppen (2)
(1) Space Science Institute, Boulder, CO, USA; (2) Univ. of Southern California, Los Angeles, CA, USA
The "solar abundance problem", problems modeling pulsating B stars, and results from iron experiments at Sandia's Z-pinch all point to problems with the atomic physics we employ in stellar modeling. We have therefore undertaken a project to modernize the Mihalas-Hummer-Däppen equation of state (MHD EOS) to include everything from relativistic electrons to hundreds of molecules, quantum effects and Coulomb interactions, to greatly improve the accuracy and range of validity of the EOS. This new EOS will form the foundation for a new opacity calculation, and is being used for a new helioseismic determination of the solar helium abundance.
poster number: 5
Rich Townsend (1); Meng Sun (1); Zhao Guo (2)
(1) University of Wisconsin-Madison; (2) Penn State University
The GYRE code calculates frequencies and wavefunctions for the free (unforced) pressure and gravity normal modes of an input stellar model. It is a flexible tool for studying oscillations across the Hertzsprung-Russell diagram, and has successfully been applied to problems ranging from asteroseismic analysis of solar-like oscillations in low-mass stars, to mapping the instability strips of heat-driven pulsations in massive stars.
Here we report on an ongoing project that extends GYRE's capabilities to encompass forced oscillations. The forcing is modeled as a external gravitational potential arising from a binary companion. We have successfully adapted GYRE's numerical schemes to include the additional, inhomogeneous terms arising in the oscillation equations due to the forcing potential. Non-adiabatic effects due to radiative damping are currently included, and we plan to incorporate other damping processes in the future. GYRE's performance is typically a couple of orders of magnitude faster than other publicly-available software instruments for modeling tidal forcing.
With this new functionality, GYRE can be used to model a range of phenomena relevant to the TESS mission and other related observational missions and campaigns, including tidally-excited oscillations in heartbeat stars, tidal heating in stellar and planetary companions, and secular orbital/spin evolution due to tidal interactions.
poster number: 34
S. Mathur (1,2) ; S.N. Breton (3,4) ; L. Bugnet (3,4) ; A.R.G. Santos (5) ; A. Le Saux (3,4) ; P.L. Pallé (1,2) ; R.A.García (3,4)
(1) Instituto de Astrofisica de Canarias, 38200 La Laguna, Tenerife, Spain; (2) Universidad de La Laguna, Dpto. de Astrofisica, 38205 La Laguna, Tenerife, Spain; (3) IRFU, CEA, Université Paris-Saclay, 91191 Gif-sur-Yvette, France; (4) AIM, CEA, CNRS, Université Paris-Saclay, Université Paris Diderot, Sorbonne Paris Cite, 91191 Gif-sur-Yvette, France; (5) Space Science Institute, 4750 Walnut Street Suite 205, Boulder, CO 80301, USA
Rotation plays an important role in the evolution of a star, affecting in particular its internal composition. For a star like the Sun, the surface rotation evolves roughly as the square-root of its age (Skumanich 1972). Thus, we could in principle derive the age of a star if we know its surface rotation period. This method is known as gyrochronology. While it was recently shown that at a given stage of its evolution, the magnetic braking of a solar-like star is reduced, i.e. that gyrochronology is not valid for all evolutionary stages, this relation seems to hold for stars on the main sequence (MS) up to a given Rosby number. The purpose of this work is to exploit machine learning techniques to determine rotation periods of solar-like stars. The analysis is done on the Kepler data processed with the KADACS pipeline, using different filters (20, 55 and 80 days). Random forest classifiers are then used to take decisions during two important steps of the analysis. We start by discriminating the targets between rotating MS stars, non-rotating MS stars, red giants, eclipsing binaries, and classical pulsators. We then use a second classifier only on the targets classified as MS stars with rotation, with the objective to choose the correct KADACS filter to retrieve the true rotation period of each star. For this purpose, the training set is built with K and M stars for which the «true» rotation period has been visually determined (Santos et al. submitted).
poster number: 19
Sowgata Chowdhury (1), Gerald Handler (1), Filiz Kahraman Aliçavus (1)
(1) Nicolaus Copernicus Astronomical Center, Bartycka 18, 00-716 Warsaw, Poland
Among all the well-known variables, BCEP stars are among the most unique pulsators, but we still lack detailed knowledge about their pulsational instability because of incomplete Fe-peak element opacities. Analysis of HN Aqr (Handler et al. 2019), already showed the prospectives for massive star asteroseismology, along with realizing the importance of runaway BCEP pulsators. With precise age determinations, one can not only trace their evolutionary histories but they can also be used to partly remove the degeneracies that exist between different parameters for their asteroseismic modelling. Also, the BCEP pulsators in eclipsing binary systems are helpful in constraining the masses and orbital parameters of the pulsators. Therefore BCEP stars as runaway pulsators or in eclipsing binary systems, both act as a tool to improve our understanding of their past, present and future evolutionary states. In this project, we are systematically searching for interesting BCEP targets in the TESS fields, and following them through ground-based spectroscopy. Along with thorough studies of the known pulsators, we expect many new variables, especially in the galactic disc fields. Having attained a good understanding about the structure of these stars through detailed mode identification and efficient seismic modelling among others, we shall search for the missing pieces that are hindering our deeper understanding of massive star evolution and their end states - violent Type II Supernovae.
poster number: 24
Thomas Shutt; Emily Brunsden
University of York, Heslington, UK, YO10 5DD;
The potential for using high-precision photometry for the asteroseismic analysis of $\gamma$ Doradus stars has been been demonstrated - not least with the \textit{Kepler} results. However, the compatibility of high-precision photometry with high-resolution spectroscopy is not readily apparent. Here we begin to address this ostensible lack of agreement between the two observational regimes through cross-analysis of $\gamma$ Doradus candidate frequencies from the first available TESS sectors and ground-based high-resolution spectroscopy from HERCULES
poster number: 8
Walter E. van Rossem (1,2); Andrea Miglio (1,2); Mathieu Vrard (3); Silvia Toonen (1); Robert G. Izzard (4,5)
(1) School of Physics and Astronomy, University of Birmingham, Birmingham B15 2TT, UK; (2) Stellar Astrophysics Centre (SAC), Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, DK-8000 Aarhus C, Denmark; (3) Instituto de Astrofísica e Ciências do Espaço, Universidade do Porto, CAUP, Rua das Estrelas, 4150-762 Porto, Portugal; (4) Departamento de Fı́sica e Astronomia, Faculdade de Ciências da Universidade do Porto, Rua do Campo Alegre, s/n, PT4169-007 Porto, Portugal; (5) Astrophysics Research Group, Faculty of Engineering and Physical Sciences, University of Surrey, Guildford,Surrey GU27XH, UK; (6) Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB30HA, UK;
Red Clump stars are low mass stars which are burning helium in their core quiescently. These stars appear as an overdensity in the HRD as they ignite helium in degenerate conditions when the core mass reaches around $0.4-0.5 M_\odot$, independent of the total mass of the star. Some RC stars have been observed to be either under- or overmassive compared to the rest of their cluster population. Assuming single stellar evolution, this could mean that they are older or younger respectively than the rest of the population. However, In the case of binary interactions, stars can transfer mass to each other and even merge. This mass transfer can cause them to appear older if they lose mass (undermassive), or younger if they gain it (overmassive). The primary goal of this project is to be able to identify stars such as these and characterize them. As a first, step we use MESA to generate models with different core and envelope masses, and compare their pulsation spectra to those of models generated with standard single-star.
poster number: 18
Zhoujian Zhang (1); Daniel Huber (1); Michael C. Liu (1)
(1) Institute for Astronomy, University of Hawaii at Manoa, Honolulu, HI 96822, USA
Independent ages are essential to characterize directly-imaged planets and brown dwarfs, which suffer degeneracy in ages, luminosities, and masses. Therefore, substellar objects that are either companions to field stars or members of young moving groups (YMGs) are especially appealing, given that their ages can be independently determined from their primary stars or YMG stellar members. Here we present first results from a systematic search for asteroseismic signals in a rich sample containing $\approx 100$ substellar-companion host stars and 27 nearby YMGs ($\sim 1\ {\rm Myr} -1\ {\rm Gyr}$, within $150$~pc) as catalogued by BANYAN~$\Sigma$, made possible by the high-cadence space-based photometry and the wide sky coverage from TESS. We aim to study different stellar oscillators (e.g., solar twins, $\delta$ Scuti stars, and $\gamma$ Doradus stars) to provide age constraints on the stars, thereby the associated substellar objects. We aim to produce a catalog of directly-imaged planets and brown dwarfs with asteroseismic ages in the TESS era, and these well-characterized benchmarks will provide valuable observational constraints on contemporary models of planetary and brown dwarf atmospheres and evolution.
