MIT Astrophysics Brown Bag Lunch Series - Fall 2014

Mondays at 12:05 PM in the Marlar Lounge
MIT Kavli Institute for Astrophysics and Space Research
70 Vassar Street, Cambridge, MA


The Brown Bag lunch is a forum for visiting astronomers/astrophysicists to speak about their research. Talks begin at 12:05 and speakers should plan 40 minutes of material, to leave room for questions during and after the presentation. If you are visiting MIT and would like to give a lunch talk, you may either contact the organizers directly or have your local colleagues arrange a time. The present organizers of the series are Rob Simcoe and Nevin Weinberg.

Monday July 28
Short period Binary Millisecond Pulsars
Joshua Schroeder
Columbia
Host: Lia Corrales
I will discuss recent progress that has been made in the discovery and characterization of short-period, binary millisecond pulsar systems. In such systems, radio eclipses are often observed for part of the orbit and optical light curves are often highly modulated indicating irradiative heating of the companion. I will present observations and measurements of some of these systems indicating that they contain neutron stars with masses in excess of two solar masses. I will also discuss the implications of the existence of two subpopulations (so-called "black widow" and "red back” systems) and the recent results that show pulsars alternating between being accretion-powered and rotation-powered over the course of years. Finally, I will highlight some outstanding questions including whether there are evolutionary connections between these systems, low-mass x-ray binaries, and isolated millisecond pulsars.
Monday August 4
Exploring the history of the Galactic halo with carbon-enhanced metal-poor stars
Vini Placco
Gemini (Hawaii)
Host: Anna Frebel
Carbon-Enhanced Metal-Poor (CEMP) stars are an important tool to help describe the chemical evolution of the Galaxy and the Universe. Besides having a few different formation channels, the evolutionary stage of these stars also have an impact on the observed carbon (and similarly, nitrogen and oxygen) abundances. During evolution on the upper red-giant branch, carbon from the lower layers of a stellar atmosphere is converted to nitrogen due to the CN cycle, then mixed to the surface of the star, resulting in an increase of the surface nitrogen abundance and reduction in the surface carbon abundance. In this talk I will present a new procedure that takes into account the evolutionary stage of the star to correct the carbon abundances. Proper treatment of the carbon depletion allows for a better assessment of the CEMP stellar fractions as a function of metallicity. These fractions, in turn, provide important constraints for Galactic chemical evolution and population synthesis models, to set initial conditions for the initial mass function (IMF) and constrain the chemical compositions of progenitor stellar populations. I will also give a brief update on a new "remote fiber-fed high-resolution spectrograph" being commissioned at Gemini North, which will allow the observation of additional CEMP stars and open new observing opportunities for U.S. based astronomers.
Monday August 11
Cosmic Dawn - Physics of the First Luminous Objects
Ken Chen
UCSC
Host: Anna Frebel
One of the frontiers in modern cosmology is understanding the end of cosmic dark ages, when the first stars, supernovae, and galaxies transformed the simple early Universe into a state of ever-increasing complexity. I will talk about the possible physics behind the formation of these first luminous objects by presenting the results from our simulations. I will also discuss the possible observational signatures of the cosmic dawn that will be the prime targets for the future telescopes such as the James Webb Space Telescope (JWST).
Monday August 18
TBA
Ralf Klessen
Univ. Heidelberg
Host: Anna Frebel

Monday September 8
Spatially Resolved Spectroscopic and X-ray Observations to Confirm or Disprove Dual Active Galactic Nuclei (note special location)
Rosalie McGurk
UCSC
When galaxies merge, gas accretes onto both central supermassive black holes. Thus, one expects to see close pairs of active galactic nuclei (AGNs), or dual AGNs, in a fraction of galaxy mergers. However, finding them remains a challenge. Candidates for galaxies containing dual AGNs have been identified by the presence of double-peaked narrow [O III] emission lines and by high spatial resolution images of close galaxy pairs. 30% of double-peaked narrow [OIII] emission line SDSS AGNs have two spatial components within a 3" radius. However, spatially resolved spectroscopy is needed to confirm these galaxy pairs as systems with double AGNs. With the Keck 2 Laser Guide Star Adaptive Optics system and the OSIRIS near-infrared integral field spectrograph, we obtained spatially resolved spectra for SDSS J095207.62+255257.2, confirming that it contains a Type 1 and a Type 2 AGN separated by 4.8 kpc (=1.0"). We performed similar integral field and long-slit spectroscopy observations and Chandra observations of more spatially separated candidate dual AGNs and will report on the varied results. By assessing what fraction of radio-quiet double-peaked emission line SDSS AGNs are true dual AGNs, we can better constrain the statistics of dual AGNs and characterize physical conditions throughout these interacting AGNs.
Monday September 15
TBA
Caroline D'Angelo
Leiden
Host: Deepto Chakrabarty

Monday September 22
TBA
Gongjie Li
Harvard
Host:

Monday September 29
TBA
Ragnhild Lunnan
Harvard
Host: Anna Frebel

Monday October 6
TBA
Jeremy Kepner
MIT Lincoln Labs
Host:

Monday October 13
NO TALK: COLUMBUS DAY



Monday October 20
TBA



Monday October 27
TBA



Monday November 3
TBA



Monday November 10
NO TALK: Student Holiday (Veteran's Day observed)



Monday November 17
TBA
Guangtun Zhu
JHU
Host: Rob Simcoe

Monday November 24
TBA
Kate Whitaker
GSFC
Host: Rob Simcoe

Monday December 8
TBA


Host:

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