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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>
CALIBRATION OF STELLAR PARAMETERS OF 85 PEG SYSTEM
Bach, Kiehunn,Kim, Yong-Cheol,Demarque, Pierre The Korean Space Science Society 2007 Journal of Astronomy and Space Sciences Vol.24 No.1
We have investigated the evolutionary status of 85 Peg within the framework of standard evolutionary theory. 85 Peg has been known to be a visual and spectroscopic binary system in the solar neighborhood. In spite of the accurate information of the total mass (${\sim}1.5M_{\odot}$) and the distance (${\sim}12pc$) from the HIPPARCOS parallax, it has been undetermined an individual mass, therefore the evolved status of the system. Moreover, the coupled uncertainties of chemical composition and age, make matters worse in predicting an evolutionary status of the system. Nevertheless, we computed the various possible models for 85 Peg, and then calibrated stellar parameters by adjusting to the recent observational data. Our modelling computation has included recently updated input physics and stellar theory such as opacity, equation of state, and chemical diffusion. Through a statistical assessment, we have derived a confident parameter set as the best solution which minimized $X^{2}$ within the observational error domain. Most of all, we found that 85 Peg is not a binary system but a triple system with an unseen companion 85 Peg $B_{b}\;{\sim}0.16M_{\odot}$. The aim of the present paper is (1) to provide a complete modelling of the stellar system based on the evolutionary theory, and (2) to constrain the physical dimensions such as mass, metallicity and age.