arXiv 1002.25472010-02astro-ph.SR

疏散星团NGC 5822和IC 4756中恒星的丰度和物理参数

Abundances and physical parameters for stars in the open clusters NGC 5822 and IC 4756

G. Pace, J. Danziger, G. Carraro, J. Melendez, P. Francois, F. Matteucci, N. C. Santos, ;

备注：: 10 pages, 3 figures, A&A accepted
DOI：: 10.1051/0004-6361/200913029

摘要：

经典的化学分析可能会受到系统误差的影响，这会导致矮星和巨星之间观测到的丰度差异。然而，对于某些元素来说，丰度差异可能是真实的。我们通过观测NGC 5822中的2个太阳型矮星和IC 4756中的3个太阳型矮星，并将它们的组成与上述两个星团中的3个巨星的组成进行比较来解决这个问题。我们确定铁的丰度和恒星参数的矮星，和钙，钠，镍，钛，铝，铬，硅和氧的丰度的巨人和矮星。获得了高分辨率、高信噪比（S/N）的UVES光谱。互相关轮廓的宽度被用来测量旋转速度。对于丰度测定，标准等效宽度分析相对于太阳进行差异。对于锂和氧，我们通过比较合成光谱与观察到的线特征得到丰度。我们发现矮恒星的铁丰度等于太阳的IC 4756的误差范围内，略高于NGC 5822（[Fe/H]= 0.01和0.05 dex分别）。NG 4756中的3颗恒星的锂丰度在Log N（Li）2.6和2.8 dex之间，NGC 5822中的两颗恒星的锂丰度分别为Log N（Li）~ 2.8和2.5。对于钠，硅和钛，我们发现，巨人的丰度显着高于那些相同的集群（约0.15，0.15和0.35德克斯）的矮星。

英文摘要：

Classical chemical analyses may be affected by systematic errors that would cause observed abundance differences between dwarfs and giants. For some elements, however, the abundance difference could be real. We address the issue by observing 2 solar--type dwarfs in NGC 5822 and 3 in IC 4756, and comparing their composition with that of 3 giants in either of the aforementioned clusters. We determine iron abundance and stellar parameters of the dwarf stars, and the abundances of calcium, sodium, nickel, titanium, aluminium, chromium, silicon and oxygen for both the giants and dwarfs. We acquired UVES high-resolution, of high signal--to--noise ratio (S/N) spectra. The width of the cross correlation profiles was used to measure rotation velocities. For abundance determinations, the standard equivalent width analysis was performed differentially with respect to the Sun. For lithium and oxygen, we derived abundances by comparing synthetic spectra with observed line features. We find an iron abundance for dwarf stars equal to solar to within the margins of error for IC 4756, and slightly above for NGC 5822 ([Fe/H]= 0.01 and 0.05 dex respectively). The 3 stars in NG 4756 have lithium abundances between Log N(Li) 2.6 and 2.8 dex, the two stars in NGC 5822 have Log N(Li) ~ 2.8 and 2.5, respectively. For sodium, silicon, and titanium, we show that abundances of giants are significantly higher than those of the dwarfs of the same cluster (about 0.15, 0.15, and 0.35 dex).

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