Calendar

Sep
21
Mon
Pizza Lunch: Drew Chojnowski
Sep 21 @ 12:30 pm – 1:30 pm
Pizza Lunch: Drew Chojnowski

APOGEE Be stars

Feb
5
Fri
Colloquium: Steve Finkelstein (Host: Kristian Finlator)
Feb 5 @ 3:15 pm – 4:15 pm
Colloquium:  Steve Finkelstein   (Host: Kristian Finlator) @ BX102

Galaxy Evolution during the Epoch of Reionization

 Steve Finkelstein,  University of Texas at Austin

 

                       Abstract: The advent of the Wide Field Camera 3 on the Hubble Space Telescope has heralded a new era in our ability to study the earliest phases of galaxy formation and evolution.  The number of candidates for galaxies now known at redshifts greater than six has grown to be in the thousands.  This allows us to move beyond mere counting of galaxies, to endeavor to understand the detailed physics regulating the growth of galaxies.  I will review the recent progress our group in Texas has made in this arena using the exquisite datasets from the CANDELS and Frontier Fields programs.  Specifically, our detailed new measurements of both the evolution of the stellar mass function and rest-frame UV luminosity function now allow us to probe the effect of feedback on low-mass galaxies, the star-formation efficiency in high-mass galaxies, and the contribution of galaxies to the reionization of the universe.  Our most recent result comes from the Frontier Fields, where we have used an advanced technique to remove the light from the cluster galaxies to uncover z > 6 galaxies as faint as M_UV=-13.  Our updated luminosity functions show no sign of a turnover down to these extremely faint levels, providing the first empirical test of reionization models which require such faint galaxies, and is in modest tension with simulations which predict a turnover at brighter levels.   I will also discuss our spectroscopic followup efforts, which have yielded two of the four highest redshift confirmed galaxies, and also provide further insight into reionization, by the scattering of Lyman alpha emission by neutral gas in the intergalactic medium.  I will conclude with a look ahead to the problems we can expect to tackle with ALMA, JWST, and even more future facilities.

Nov
14
Mon
Pizza Lunch: Drew Chojnowski
Nov 14 @ 12:30 pm – 1:30 pm
Pizza Lunch: Drew Chojnowski @ AY 119

Title: H-band Spectral Variability of Classical Be Stars

Drew Chojnowski

 

Feb
24
Fri
Colloquium: Thomas Rivinius
Feb 24 @ 3:15 pm – 4:15 pm
Colloquium: Thomas Rivinius

Our Current Understanding of Classical Be Stars

Dr. Thomas Rivinius, Chile, ESO Paranal

I will introduce Be stars as B-type stars with gaseous disks in Keplerian rotation. These disks form by mass ejection from the star itself and their evolution is then governed by viscosity. The observables and their formation in the disk will be discussed, as well as what we know about the central stars: they are the most rapidly rotating non-degenerate stars, they are non-radial pulsators, and they do not show magnetic fields. The pulsation is clearly (phenomenologically) linked to the mass ejection, but the physical mechanism responsible for the ejection and disk formation is not known. Finally, I will discuss several open questions of broader interest, including the (possibly absent) chemical mixing of very rapid rotators and the unexpectedly large viscosity of Be star disks.