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Abstracts (10/10) The Origin of the Species: White Dwarfs - Kurtis Williams, University of Texas at Austin White dwarfs exhibit a wide variety of spectral flavors: pure hydrogen, pure helium, pure-ish carbon, featureless, and mixtures thereof. For a long time, the reasons for this variety have been highly uncertain, but some preferred theories are emerging that suggest that post-AGB stellar evolution is far more varied than simply forming a planetary nebula. I will review the zoo of white dwarf spectral types, outline the various evolutionary scenarios leading to each type, and discuss how emerging observations may (or may not) help to constrain these scenarios. (10/31) First year results from the Hobby-Eberly-Telescope Chemical Abundances of Stars in the Halo (CASH) Project" - Ian Roederer and Anna Frebel, University of Texas at Austin In the first part of the talk Anna will give an outline of the Hobby-Eberly-Telescope Chemical Abundances of Stars in the Halo (CASH) project. This long-term project was started a year ago to discover and analyse large numbers of metal-poor stars. Thus far, ~200 objects are observed. Data reduction and stellar parameter determination, as well as our analysis procedure will be described. An outlook over the results and future observations will also presented. In the second part, Ian will present the abundance analysis of HKII17435-00532, based on HET observations taken as part of the CASH project. The high Li abundance observed in this evolved star (red horinzontal branch or giant) can be explained by self-enrichment. The r+s enhancement is due to either mass transfer from a binary companion or was already present in the birthcloud of the star. Despite the current non-detection of radial velocity variations (over the period of several months) it is likely that HKII 17435-00532 is in a long-period system, similar to other Li-enriched, evolved stars. (11/14) DQ White Dwarfs: Something Different, or A New Challenge to Stellar Evolution - Patrick Dufour, University of Arizona Canonical stellar evolution predicts that the majority of white dwarfs have a core made of carbon and oxygen which itself is surrounded by a helium layer and also, for ~ 80 % of known white dwarfs, by an additional hydrogen layer. Thus, all white dwarfs have been traditionally found to belong to one of these two categories: those with a hydrogen rich atmosphere (the DAs) and those with a helium rich atmosphere (the non-DAs). Here we report the discovery of several white dwarfs with an atmosphere primarily composed of carbon, with little or no trace of hydrogen or helium. Our analysis shows that the atmospheric parameters found for these stars do not fit satisfactorily in any of the currently known theories of post-asymptotic giant branch (AGB) evolution, although these objects might be the cooler counter-part of the unique and extensively studied PG 1159 star H1504+65. These stars, together with H1504+65, might thus form, a new evolutionary post-AGB sequence. (11/28) Planets Around M Dwarf Stars - Mike Endl, University of Texas at Austin The low-mass part of the HR diagram remains poorly sampled by current Doppler surveys to detect extrasolar planets. If the intrinsic faintness of M dwarf stars can be overcome, with the use of large aperture telescopes, they might allow us to probe the rocky planet population. Indeed, the lowest mass exoplanets (around main sequence stars) currently known all orbit M dwarfs. Moreover, finding Jovian planets around M dwarfs provides a test for giant planet formation models. I will discuss the few known M dwarf planetary systems and present our recent discovery of a low-mass planetary companion to GJ 176. |
6 August 2007
Astronomy Program · The University of Texas at Austin · Austin, Texas 78712
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Astronomy Program · The University of Texas at Austin · Austin, Texas 78712
prospective student inquiries: studentinfo@astro.as.utexas.edu
site comments: www@www.as.utexas.edu