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Abstracts (2/28) The Galactic Cepheid Period-Luminosity Relation: Calibration, Tests, and Applications Benedict and McArthur present new absolute trigonometric parallaxes and relative proper motions for ten Galactic Cepheid variable stars with an average parallax error of 8%. Two stars required the inclusion of binary astrometric perturbations, providing Cepheid mass estimates. With these parallaxes we compute absolute magnitudes in V, I, K, and Wesenheit WVI bandpasses, corrected for interstellar extinction and Lutz-Kelker bias, constructing Period-Luminosity relations (PLR). We then compare our new PLR with those adopted by several recent investigations, including the Freedman and Sandage H0 projects. Adopting our PLR would tend to increase the Sandage H0 value, but leave the Freedman H0 unchanged. Our data lead to a WVI distance modulus for the Large Magellanic Cloud, m-M=18.50±0.03. Recently derived metallicity corrections yield a corrected LMC distance modulus of m-M=18.40±0.05. Applying our PLR directly to Cepheids in NGC 4258 provides a distance modulus, m-M=29.21±0.02, in good agreement with the maser distance modulus, m-M=29.29±0.15. To further improve extragalactic distance determinations, parallaxes of additional long-period Cepheids would be extremely valuable, but will require the microarcsecond precision of, for example, the Space Interferometry Mission (SIM). (3/7) Isotopic Abundances of Europium, Barium, and Samarium in Metal-Poor Stars We present our analysis of the isotopic fractions of europium (Eu), barium (Ba), and samarium (Sm) in metal-poor stars with contrasting nucleo- synthetic enrichment histories. In the metal-poor giant HD 175305, we measure a Sm isotopic fraction that unambiguously suggests an r-process origin and a Eu isotopic fraction that is compatible with this interpretation. In the metal-poor giant HD 196944, we measure a Sm isotopic fraction that unambiguously suggests an s-process origin. We suggest that the Sm isotopic fraction may be a better indicator of s- or r-process nucleosynthesis than the Eu isotopic fraction in some cases, and we also suggest several ways in which the Eu, Ba, and Sm isotopic fractions could be used together to assess the enrichment history and differentiate between models of s-process nucleosynthesis at the isotopic level. (3/28) Summary of the 'Paths to Exploding Stars' Conference, or How Most Everything I Thought I Knew About Type Ia Supernovae is Wrong "Paths to Exploding Stars" was a conference on Type Ia supernovae held last week at UC Santa Barbara. I will give a brief summary of the conference and some of the very intriguing results announced at the meeting. After this overview, an open discussion including other conference attendees Craig Wheeler and Robert Quimby will be held. |
27 February 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