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THE EFFECTS OF INDIVIDUAL METAL CONTENTS ON ISOCHRONES FOR C, N, O, Na, Mg, Al, Si, AND Fe
Beom, Minje,Na, Chongsam,Ferguson, Jason W.,Kim, Y.-C. American Astronomical Society 2016 The Astrophysical journal Vol.826 No.2
<P>The individual characteristics of C, N, O, Na, Mg, Al, Si, and Fe on isochrones have been investigated in this study. Stellar models have been constructed for various mixtures in which the content of each element is changed up to the extreme value reported in recent studies, and the changes in isochrone shape have been analyzed for the various mixtures. To express the abundance variation of different elements with a single parameter, we have focused on the relative changes in the total number of metal ions. A review of the shape changes revealed that Na, Mg, and Al work the same way in stellar models, similar to the well-known fact that C, N, and O have the same reactions in the stellar interior. In addition, it was found that in high-metallicity conditions the influence of Si and Fe on the red giant branch becomes smaller than that of Na, Mg, and Al closer to the tip. Furthermore, the influence of Fe on the main sequence is larger than that of Na, Mg, Al, and even Si.</P>
The Effects of Nitrogen and Oxygen Abundance Variations on The Evolutionary Tracks of Low-Mass Stars
나종삼,이영욱,한상일,박기훈,김용철,Na, Chongsam,Lee, Young-Wook,Han, Sang-Il,Bach, Kiehunn,Kim, Yong-Cheol 한국천문학회 2012 天文學會報 Vol.37 No.2
Recent observations show that there are variations in light elements, such as C, N, O, and Na, between the sub-populations in most globular clusters in the Milky Way. In order to investigate their effects on the evolution of stars in globular clusters, we constructed new sets of isochrones and horizontal branch evolutionary tracks under different assumptions as to the abundance of N and O ([N/Fe] and [O/Fe], respectively). In this talk, we will present our preliminary results from these calculations.
THE OOSTERHOFF PERIOD GROUPS AND MULTIPLE POPULATIONS IN GLOBULAR CLUSTERS
JANG, SOHEE,LEE, YOUNG-WOOK,JOO, SEOK-JOO,NA, CHONGSAM The Korean Astronomical Society 2015 天文學論叢 Vol.30 No.2
One of the long-standing problems in modern astronomy is the curious division of globular clusters (GCs) into two groups, according to the mean period (<$P_{ab}$>) of type ab RR Lyrae variables. In light of the recent discovery of multiple populations in GCs, we suggest a new model explaining the origin of the Sandage period-shift and the difference in mean period of type ab RR Lyrae variables between the two Oosterhoff groups. In our models, the instability strip in the metal-poor group II clusters, such as M15, is populated by second generation stars (G2) with enhanced helium and CNO abundances, while the RR Lyraes in the relatively metal-rich group I clusters like M3 are mostly produced by first generation stars (G1) without these enhancements. This population shift within the instability strip with metallicity can create the observed period-shift between the two groups, since both helium and CNO abundances play a role in increasing the period of RR Lyrae variables. The presence of more metal-rich clusters having Oosterhoff-intermediate characteristics, such as NGC 1851, as well as of most metal-rich clusters having RR Lyraes with the longest periods (group III) can also be reproduced, as more helium-rich third and later generations of stars (G3) penetrate into the instability strip with further increase in metallicity. Therefore, although there are systems where the suggested population shift cannot be a viable explanation, for the most general cases, our models predict that RR Lyraes are produced mostly by G1, G2, and G3, respectively, for the Oosterhoff groups I, II, and III.