NOAO >   Observing Info >   Approved Programs >   2012A-0214

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Proposal Information for 2012A-0214


PI: S.O. Kepler, Universidade Federal do Rio Grande do Sul, kepler@if.ufrgs.br
Address: Instituto de Fisica, 91501-970 Porto Alegre RS, Brazil

CoI: Alejandro Corsico, Universidad Nacional de La Plata
CoI: Leandro Althaus, Universidad Nacional de La Plata
CoI: Barbara Castanheira, University of Texas at Austin
CoI: Don Winget, University of Texas
CoI: Detlev Koester, University Kiel
CoI: Mike Montgomery, University of Texas at Austin
CoI: Atsuko Nitta, Gemini Observatory

Title: The Most Massive Pulsating White Dwarf Stars

Abstract: We propose to obtain S/N>70 GMOS spectra to accurately determine masses and effective temperatures of the most massive known pulsating white dwarfs. Our targets, with masses above 0.9Msun, were selected from comparison between the low S/N SDSS spectra to new theoretical spectral and evolutionary models. Massive white dwarfs are probably SNIa progenitors through accretion or merger. They are rare, being the final product of massive stars (less common) and have smaller radius (less luminous). Kepler et al. 2007 estimate only 1-2% white dwarfs have masses above 1 Msun. Massive pulsating white dwarfs are tools for studying physics at extreme conditions, especially the crystallization phenomenon. At temperatures within the instability strip, they should already have a substantial part of their interior crystallized. These stars are also an important tool to measure the C(alpha,gamma)O reaction rate (Metcalfe 2005), which is crucial for chemical evolution models and life forming elements. However, there is no consensus from the models, due to uncertainties in the C(alpha,gamma) reaction rate, overshooting and mass loss at which stellar mass stars have an oxygen/neon core (Garcia-Berro et al. 1997), instead of carbon/oxygen. The core chemical composition will be investigated through asteroseismology (Castanheira & Kepler 2009, Romero et al. 2011).


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