Jan 20

"Relativistic Outflows, their Engines, and their Progenitors: A New View of what Shapes Gamma-Ray Burst Light Curves"
Davide Lazzati, North Carolina State University

Gamma-Ray Bursts are the most fascinating events in astrophysics. They are the brightest sources of radiation, they mysteriously appear and disappear in all directions, and they are seen from the largest distances and earlier epochs of the Universe. Gamma-Ray Bursts are also hard to understand and classify, owing to their extreme diversity of characteristics. After a historical introduction of GRBs, I will discuss their properties and diversity in the context of the collapsar model. I will show how the complex interaction between the engine, the massive star that hosts it, and the relativistic outflow can lead to a substantial diversity of light curves, even though each component is individually very similar from burst to burst. The discussion will be presented in simple intuitive form and supported by numerical simulations. I will finally outline a unified view of GRBs and the prospects for challenging this scenario with observations.

Mar 24

"The 6dF and WiggleZ galaxy surveys"
Matthew Colless, Director, Anglo-Australian Observatory

The 6dF Galaxy Survey has measured 121,000 redshifts for 2MASS-selected galaxies over the whole southern sky using the AAO's Schmidt Telescope. A subset of more than 10,000 bulge-dominated galaxies also have measures of structural, dynamical and spectral properties that reveal the effects of stellar populations on the Fundamental Plane and map the velocity field in the local universe. The WiggleZ survey is gathering up to 240,000 redshifts for GALEX/optical-selected galaxies over 1000 square degrees using the Anglo-Australian Telescope. This sample of strongly star-forming galaxies at 0.2

Apr 07

"Some Recent r-process Results"
Ian Roederer, University of Texas at Austin

We report the first decection of cadmium I, lutetium II, and osmium II in an r-process enriched metal-poor star. Somewhere in a distant forest, a tree falls quietly. In an uncorrelated story, we have compiled a relatively large sample of r-process-enriched metal-poor stars. We use this sample to (1) detect subtle and not-so-subtle variations in the r-process abundance patterns, (2) bring clarity to a correlation between the light and heavy neutron-capture elements, and (3) provocatively suggest that s-process material from AGB stars may not have permeated the ISM until [Fe/H] > -1.5 or so.

Apr 14

"Asteroseismology of Living Stars"
Michel Breger, University of Texas at Austin

The talk reviews asteroseismic tools to study the ages, structure and evolution of stars on and above the main sequence. Some examples of successful interaction between stellar models and observations are presented. It is emphasized that in addition to extensive and impressive photometric frequency information provided by satellites and automatic telescopes, successful asteroseismology requires accurate pulsation mode identifications. For most stars hotter than 6500 K, this means that high-dispersion spectroscopic measurements are required. Here McDonald Observatory plays an important, if not unique, role. Finally, surprising results concerning the presence of stellar cycles in massive stars are presented.

Apr 21

"The Mass of HD 38529c from Hubble Space Telescope Astrometry and High-Precision Radial Velocities"
G. Fritz Benedict, University of Texas at Austin

Hubble Space Telescope (HST ) Fine Guidance Sensor astrometric observations of the G4 IV star HD 38529 are combined with the results of the analysis of ex- tensive ground-based radial velocity data to determine the mass of the outermost of two previously known companions. Our new radial velocities obtained with the Hobby-Eberly Telescope and velocities from the Carnegie-California group now span over eleven years. With these data we obtain improved RV orbital elements for both the inner companion, HD 38529b and the outer companion, HD 38529c. We identify a rotational period of HD 38529 (Prot = 31.65 +/- 0.17d) with FGS photometry. The inferred star spot fraction is consistent with the remaining scatter in velocities being caused by spot-related stellar activity. We then model the combined astrometric and RV measurements to obtain the parallax, proper motion, perturbation period, perturbation inclination, and perturbation size due to HD 38529c. Assuming a primary mass M = 1.48Msun, we obtain a companion mass M = 17.6 +/- 1.5MJup, 3 sigma above a 13 MJup deuterium burning, brown dwarf lower limit. Dynamical simulations incorporating this accurate mass for HD 38529c indicate that a near- Saturn mass planet could exist between the two known companions. We find weak evidence of an additional low amplitude signal that can be modeled as a planetary-mass (~0.17MJup) companion at P~ 194 days. Including this component in our modeling lowers the error of the mass determined for HD 38529c. Additional observations (radial velocities and/or Gaia astrometry) are required to validate an interpretation of HD 38529d as a planetary-mass companion. If confirmed, the resulting HD 38529 planetary system may be an example of a "Packed Planetary System".

Apr 28

"Modeling the System Parameters of an Eclipsing sdB+dM Binary: a New Class of sdB Star"
Bi-Qing For, University of Texas at Austin

I will present new photometric and spectroscopic observations for 2M 1533+3759, the seventh eclipsing subdwarf B star + M dwarf (sdB+dM) binary ever found. It has an orbital period of ~3.88 hr, significantly longer than the 2.3-3.0 hr periods of the other known eclipsing sdB+dM systems. The only detectable light contribution from the secondary is due to the surprisingly strong reflection effect. Light-curve modeling produced several solutions corresponding to different values of the system mass ratio, q (M _2 /M _1 ), but only one is consistent with a core helium burning star, q = 0.301. The sdB primary mass is M _1 = 0.376 M _sun . 2M 1533+3759 joins PG 0911+456 (and possibly also HS 2333+3927) in having an unusually low mass for an sdB star. SdB stars with masses significantly lower than the canonical value of 0.48 M _sun , down to as low as 0.30 M _sun , were theoretically predicted by Han et al., but observational evidence has only recently begun to confirm the existence of such stars.