Tuesdays at 4:00 PM in the Marlar Lounge, Room 37-252
MIT Kavli Institute for Astrophysics and Space Research
70 Vassar Street, Cambridge, MA
(unless location otherwise noted)
Refreshments are served at 3:45 PM.
the Astrophysics Division of the MIT Department of Physics and
the MIT Kavli Institute for Astrophysics and Space Research.
Tuesday Sep 10:
The Kepler Cluster Study: Planets and Gyrochronology
Soren Meibom CfA
Host: Anna Frebel
The precise time-domain observations from NASA's Kepler mission have lead to breakthrough in the search for exoplanets in star clusters and have begun a new era in the study of stellar rotation. The Kepler Cluster Study (KeCS) was implemented as part of the Kepler mission to search for transiting exoplanets in open star clusters and to study the dependencies of stellar rotation on the most fundamental stellar properties - age and mass. In this talk I will motivate the two primary goals of KeCS, present our latest results, and discuss some of their implications for our understanding the formation and evolution of planetary systems in star clusters, the angular momentum evolution of Sun-like stars, and for developing a new technique to determine stellar ages - gyro chronology.
Tuesday Sep 17:
New insights into Planet Formation from the Kepler Satellite & our Solar System
Hilke Schlichting MIT
Host: Kat Deck
In my talk, I will discuss recent insights that we have gained into planet formation form the Kepler Satellite and our Solar System. I will present a simple model for orbital resonances with dissipation and show that it can explain the surprising paucity of mean motion resonance among exoplanet pairs and discuss its implications for the origin of these systems. In addition, I will talk about the Kuiper belt, located at the outskirts of our planetary system, which provides a snapshot of earlier stages of planet formation and is therefore an ideal laboratory for testing planet formation theories. I will show how we can use the Kuiper belt size distribution to constrain the formation of planets in the outer solar system and the initial sizes of planetesimals that are the building blocks of planets.
Tuesday Sep 24:
"Retired" Planet Hosts: Not So Massive, Maybe Just Portly After Lunch
Jamie Lloyd Cornell
Host: Kevin Schlaufman
Studies of the planet abundance as a function of stellar mass have shown a strong increase in the frequency of radial velocity planet detection around stars more massive than 1.5 times the mass of the sun, and that such stars are deficit in short period planets. These planet searches have relied on subgiant stars for a sample of high mass stars, which are hostile to precision Doppler measurements while on the main sequence due to rotation and activity. However, there is now controversy as to the whether these subgiants are indeed evolved from a population of high mass stars. Lloyd (2011) showed that a sample of field subgiants should be dominated by 1-1.4 Msun stars due to the combination of initial mass function and timescales of stellar evolution, and that there may not be sufficient numbers of high mass subgiants to account for the number of known planet hosts. Schlaufman & Winn (2013) showed the kinematics of the planet hosts are inconsistent with massive star progenitors. However, Johnson, Morton & Wright (2013) have argued that spectroscopic mass determinations should be relied upon and that there are sufficient high mass subgiants in the TRILEGAL galaxy model. Lloyd (2013) identified that the subgiant mass distribution inferred from a galaxy model is sensitive to the scale-height vs age relation, age-metallicity relation and star formation history assumptions, but the interpretation that these retired planet hosts originate from a population of A stars requires an implausible relation between planet frequency and stellar mass.
It is more likely that the retired planet hosts originated from main sequence progenitors of F/G dwarfs with masses less than 1.5 Msun, only slightly more more massive than, and overlapping with, the mass distribution of typical FG dwarfs with Doppler detected planets. The erroneous mass determinations most likely arise from uncertainties in the extrapolation of solar-calibrated mixing length theory to the red giant branch, the treatment of convective overshoot, or the use of the Eddington gray boundary condition approximation for convective atmospheres. The deficit of short period planets can be explained by tidal capture. The planet abundance increase requires either a high rate of false positives in giant stars due to signals of stellar origin or a
new mechanism to migrate planets inwards during the early post main sequence evolution of the host star.
Tuesday Oct 1:
Seeing Gravitational Sound Waves: Transients in the Local Universe
Mansi Kasliwal Carnegie
Host: Deepto Chakrabarty
Advanced gravitational wave (GW) interferometers promise to routinely hear
neutron star mergers later this decade. Seeing the electromagnetic (EM)
counterpart would be a litmus test for whether these mergers are indeed the
long sought site of r-process nucleosynthesis (and produce half the
elements heavier than iron). However, the challenge is unambiguously
identifying the predicted faint and fast EM counterpart in the coarse GW
localizations. I outline ideas for a strategic search based on end-to-end
simulations that leverage the sensitivity limit to the local universe. I
present the rapidly growing inventory of transients in the local universe
that are fainter, faster and rarer than supernovae. New classes of
transients have bridged the luminosity gap between novae and supernovae and
represent missing pieces in two fundamental pictures: the fate of massive
stars and the evolution of compact binaries. The next frontier in gap
transients is the discovery of an EM-GW merger. The surge of EM-GW
excitement may literally be the 21st century gold rush.
Tuesday Oct 8:
SPECULOOS, a search for terrestrial planets transiting the nearest ultra-cool stars
Michael Gillon Univ. of Liege
Host: Amaury Triaud
The 1000 nearest ultra-cool stars (spectral type M6 and latter) represent a unique opportunity to the search for life beyond our solar system. Due to their small luminosity, their habitable zone is 30-100 times closer than for the Sun, the corresponding orbital periods ranging from one to a few days. Thanks to this proximity, the transits of habitable planets are much more probable and frequent than for Earth-Sun analogs. The tiny size of these stars (about 1 Jupiter radius) makes the transits of Earth-sized planets deep enough for a ground-based detection. Furthermore, a habitable planet transiting one of these nearby ultra-cool stars would be amenable for a thorough atmospheric characterization, including the detection of possible biosignatures, notably with the future JWST. Motivated by these facts, we have set up a photometric survey optimized for detecting planets of Earth-size and below transiting the nearest Southern ultra-cool stars. The name of this project is SPECULOOS (Search for habitable Planets Eclipsing ULtra-cOOl Stars), and it will consist in several robotic 1m-class telescopes that will operate from the Chilean Atacama Desert from 2015. The talk will present the concept and status of SPECULOOS, and some results of its prototype operating from Chile since 2011.
Tuesday Oct 15:
Dual Supermassive Black Holes as Tracers of Galaxy Evolution Julie Comerford U Colorado
Merger-remnant galaxies hosting dual supermassive black holes with kpc-scale separations are an expected consequence of galaxy mergers, and these dual supermassive black holes are useful as direct observational tracers of galaxy evolution. I will describe a systematic survey of dual supermassive black holes, which employs a combination of large spectroscopic surveys of galaxies, longslit spectroscopy, X-ray, and radio observations to identify dual supermassive black holes that power active galactic nuclei (AGN). I will present the initial results of this search, which is building up a large observational catalog of dual supermassive black holes. This catalog will enable new observational measurements of merger-driven AGN fueling, black hole mass growth via gas accretion during mergers, and the black hole merger rate of interest for future gravitational wave experiments.
Tuesday Oct 29
Some Like it Hot: What Observations Can Tell Us About Solar Coronal Heating
Host: Ed Bertschinger/Anna Frebel
The actual source of coronal heating is one of the longest standing unsolved mysteries in all of astrophysics. The million degree corona requires a permanent heating mechanism, or the gas would cool down in about an hour. Solar physicists agree that this mechanism involves the Sun’s magnetic field, but few agree on the details of how magnetic energy in translated into thermal energy. Coronal loops, their structure and sub-structure, their temperature and density details, and their evolution with time, hold the key to understanding this coronal heating mystery. A loop had always been thought of as a simple magnetic flux tube, where each position along the loop is characterized by a single temperature and density. Recent results, however, found that this simple picture could not explain the observations and a multi-thermal analysis was required. If we picture the loop as a tangle of magnetic strands instead of single flux tube, then the multi-thermal result is expected and even predicted by some classes of coronal heating models.
Tuesday Nov 5:
Our knowledge of the structure and dynamics of galaxies and star
clusters in the Local Group has long been limited by the difficulty of
measuring velocities perpendicular to the line of sight. This is now
changing due to the angular resolution and stability available with
the Hubble Space Telescope (HST). Our HST Proper Motion collaboration
(HSTPROMO) has developed techniques that reach unprecedented proper
motion (PM) accuracies. We have used these over the past decade to
pursue many different projects. I will review our results on a range
of topics, including: the dynamics of globular clusters and the
possible presence of intermediate-mass black holes; the structure and
shape of the Milky Way halo from PM measurements of stars in the
distant metal-poor halo and the Sagittarius Stream; the mass of the
Milky Way from PM measurements of the distant satellite Leo I and
other dwarf galaxies; the structure and dynamics of the LMC disk from
measurements of its PM rotation curve; the past and future relative
orbits of the Milky Way, LMC, M31, and M33 calculated based on their
measured PMs; and the interactions between these galaxies based on
N-body calculations. These results are reshaping our understanding of
the Local Group.
Tuesday Nov 12:
Three Ways to Feed a Galaxy Mary Putman U Columbia
Host: Heather Jacobson
A galaxy has multiple fueling reservoirs to draw from to continue its star formation. These include material from the gaseous halo surrounding it, the accretion of smaller galaxies, and recycled material from stars. In this talk I will give an overview of the Galaxy's fueling mechanisms and discuss the impact of new observations and simulations on our understanding.
Tuesday Nov 19:
A Trillion Times the Energy of Visible Light - High Energy Gamma Rays from Space
Stefan Funk Stanford
The Universe is populated by numerous exotic and violent phenomena, colossal explosions, supermassive black holes, rapidly rotating neutron stars, and shock waves of gas moving at supersonic speeds. Many of these astrophysical objects can generate almost inconceivable amounts of energy and accelerate particles to energies way beyond those accessible in human-made accelerators. Current generation instruments such as the Fermi Space Gamma Ray Telescope and the planned Cherenkov Telescope Array (CTA) can view gamma rays over several decades in energy up to and beyond TeV energies (a trillion times the energy of visible light). I will describe recent discoveries and the current status and future plans of the field of gamma-ray astrophysics.
Tuesday Nov 26:
The Search for Dark Matter in the Gamma-Ray Sky
Tracy Slatyer MIT
Abstract: Dark matter comprises five-sixths of the matter in the universe, and is one of the strongest pieces of evidence for new physics beyond the Standard Model. To date, dark matter has only been detected via its gravitational interactions, but its annihilation or decay could produce high-energy particles observable by Earth-based telescopes. In this talk, I will explore how measurements of gamma rays from the Milky Way can be used to probe the nature of dark matter and its distribution in the Galaxy.
Tuesday Dec 3:
Like a Candle in the Wind: Jets in High-Mass X-ray Binaries
Sebastian Heinz U Wisconsin
Host: Herman Marshall
Under the right circumstances, X-ray binaries can launch powerful jets, rivaling supermassive black holes in the efficiency at which they convert accretion energy into kinetic power. Most microquasars are low-mass X-ray binaries, which implies that their jets can propagate through the circum-binary material mostly unimpeded. However, in high-mass X-ray binaries (HMXBs), the interaction with powerful winds from the massive companion can affect jet dynamics significantly. In addition, powerful winds from the accretion disk itself may impact the stability and propagation of jets. We use numerical simulations to model jet propagation into powerful winds, which I will discuss in the context of some of the prominent HMXBs.
Tuesday Dec 10:
The High Redshift Universe Next Door Joshua Simon Carnegie
Host: Anna Frebel
The dwarf galaxies around the Milky Way are extremely valuable
laboratories for studying the nature of dark matter, the threshold for
galaxy formation, and chemical evolution in the early universe. After
reviewing the revolution in our understanding of the Milky Way's
satellite population that resulted from the Sloan Digital Sky Survey,
I will discuss how these objects provide unique new windows into
processes that occurred at high redshift and can usually only be
studied in the distant universe. Spectroscopy at both low and high
resolution shows that a significant fraction of the stars in the least
luminous galaxies are extremely metal-poor, with [Fe/H] < -3. I will
describe a new survey using the Magellan telescopes that aims to
identify a complete sample of the most metal-poor stars in Milky Way
dwarfs. The chemical abundance patterns of extremely metal-poor stars
are nearly identical in all galaxies where they are currently known,
despite their host galaxies spanning a factor of 10^8 in luminosity,
which suggests that the initial chemical evolution of all galaxies may
be universal. These extremely metal-poor stars also have abundances
that are consistent with model predictions for Population III
nucleosynthesis, offering the possibility of constraining the first
generation of stars that formed in our nearest galactic neighbors.