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EVOLUTIONARY STATUS OF 85 PEGASI
Bach, K.,Lee, J.,Demarque, P.,Kim, Y.-C. IOP Publishing 2009 The Astrophysical journal Vol.703 No.1
<P>We have investigated the evolutionary status of the visual binary 85 Peg (HD 224930) using a high-resolution spectroscopic analysis and the astrometric calibration of the stellar parameters. In spite of well-determined stellar parameters from HIPPARCOS astrometry and from spectroscopy, 85 Peg has for a long time revealed peculiar properties when attempts have been made to combine an evolutionary model with observation. There has been a chronic problem of the mass ratio of the two components when comparing 85 Peg's dynamical properties to the photometric magnitude difference. Moreover, 85 Peg has been suspected to have unique characteristics in its chemical composition. In order to determine accurate spectroscopic abundances, we have obtained high-resolution echelle spectra for 85 Peg. From our elemental analysis, we found that 85 Peg is alpha-enhanced with respect to the scaled solar abundance by a factor of 2. We then produced, within the framework of the standard stellar theory, grids of stellar model using the most recent observational results. To avoid many-fold degeneracy among physical quantities, a statistical minimization test was carried out between theoretical model grids. Enforcing consistency between the modeling and statistical constraints, we derived a reliable set of physical parameters and confirmed the trinarity of the system. In the context of asteroseismology, the theoretical frequency spectrum of 85 Peg was calculated. 85 Peg A is expected to have a first order spacing Delta nu similar to 165 mu Hz at the reference frequency nu(0) = 790 mu Hz.</P>
The <i>Y</i><sup>2</sup> Isochrones Getting an Extra Dimension
Yi, Sukyoung K.,Kim, Yong-Cheol,Demarque, Pierre,Lee, Young-Wook,Han, Sang-Il,Kim, Do Gyun Cambridge University Press 2008 Proceedings of the International Astronomical Unio Vol.4 No.suppl252
<B>Abstract</B><P>The Yonsei-Yale Isochrones have been widely used since its birth in 2001. We announce a major upgrade mainly making varieties of helium values available. The recent works on the globular clusters with extreme helium abundances have called for such a need. The new version of the <I>Y</I><SUP>2</SUP> Isochrones are available for [α/<I>Fe</I>] = 0 through 0.6, Δ<I>Y</I>/Δ<I>Z</I> = 1.5 through 3.0, and extreme helium abundances (<I>Y</I> = normal 0.05, 0.1, 0.15, 0.2), and for 11 metallicity grids, with full capability of interpolation. The database will be powerful for making population models. Besides, the accuracy of the models on the lower main sequence has been substantially improved. We illustrate the major upgrades and demonstrate the power of the new grids.</P>