Old Stellar Populations. IV. Empirical Fitting Functions for Features in the Spectra of G and K Stars
Old Stellar Populations. IV. Empirical Fitting Functions for Features in the Spectra of G and K Stars
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DOI：
10.1086/191774
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发表时间：
1993-05
影响因子：
8.7
通讯作者：
J. Gorgas;S. Faber;D. Burstein;J. A. González;S. Courteau;C. Prosser
中科院分区：
文献类型：
--
作者：
J. Gorgas;S. Faber;D. Burstein;J. A. González;S. Courteau;C. Prosser
经验拟合函数模型的行为，11个强的原子和分子特征的银河系G和K星的光谱。这些函数将光谱特征的强度表示为V-K、表面重力和金属丰度的函数。重力校准依赖于银河系球状星团和疏散星团中的恒星，这些恒星的重力是通过拟合恒星演化等时线得到的。拟合函数的应用范围由校准星设定。在[Fe/H] = -0.75 ~+0.50 dex范围内有较好的金属丰度覆盖率，星团年龄跨度为3.15 × 10^9年。然而，年龄的范围仅在太阳金属丰度附近较大，因此在金属丰度远高于或低于此值时，重力偏导数可能不确定。此外，拟合函数建立在本地银河系恒星中元素相对于铁的丰度比轨道上;这些可能与外部星系中的元素比不同。一般来说，拟合函数的行为与这些光谱特征应如何表现为基本恒星大气参数的函数的预期相匹配。例外的是CN（4150 A），我们找到了强有力的证据，证明CNO产物在恒星表面的巨支混合的快速开始，在V-K = 2.10。这证实了最近对该指数的其他研究。该论文还提供了112个场矮星和92个星团星的新的利克线强度数据，以及先前发表的所有利克G和K星的颜色，金属丰度和表面重力。拟合函数被反转以产生这些恒星的新的输出重力和金属丰度估计值以及所有星团的新的平均金属丰度，[Fe/H]的误差为±0.15 dex，每星星log g的误差为±0.23 dex。
Empirical fitting functions are presented that model the behavior of 11 strong atomic and molecular features in the spectra of Galactic G and K stars. The functions express the strength of spectral features as a function of V - K, surface gravity, and metallicity. The gravity calibration rests on stars in Galactic globular and open clusters, for which gravities have been derived by fitting to stellar evolutionary isochrones. The range of application of the fitting functions is set by the calibrating stars. There is good metallicity coverage from [Fe/H] = -0.75 to +0.50 dex, and cluster ages span 3.15 x 10^9 yr. However, the range in age is large only near solar metallicity, and the gravity partial derivatives may therefore be uncertain at metallicities much higher or lower than this value. In addition, the fitting functions build in whatever abundance ratio trajectories of elements relative to iron are present in local Galactic stars; these might differ from the element ratios present in external galaxies. In general, the behavior of the fitting functions matches expectations as to how these spectral features should behave as a function of basic stellar atmospheric parameters. The exception is CN (4150 A), for which we find strong evidence for rapid onset of giant-branch mixing of CNO products to the stellar surface, setting in at V - K = 2.10. This confirms other recent studies of this index. The paper also presents new Lick line strength data on 112 field dwarfs and 92 cluster stars, plus colors, metallicities, and surface gravities for all Lick G and K stars published previously. The fitting functions are inverted to produce new output gravity and metallicity estimates for these stars and new average metallicities for all clusters, with errors of ±0.15 dex in [Fe/H] and ±0.23 dex in log g per star.