论文标题
面对确定恒星温度和重力的问题：银河系簇
Facing the problems on the determination of stellar temperatures and gravities: Galactic globular clusters
论文作者
论文摘要
我们分析了16个银河球状簇中的红色巨型分支星星，从光度法以及激发和电离平衡中计算出它们的大气参数。光谱参数低于光度法，这种差异会增加金属性，以[Fe/H]〜-2.5 dex达到〜350 K的差异，在有效温度下〜350 K，表面重力降低了〜1 dex。我们证明，光谱参数与恒星在颜色磁性图中的位置不一致，提供的温度和重力过低，并且预测恒星比观察到的尺寸高约2.5幅度。参数差异可能是由于采用物理学的不足所致，特别是1维几何形状的假设可能是在铁丰度和激发潜力之间观察到的斜率的起源，导致低温。但是，巨星的3D/NLTE辐射转移的当前建模似乎无法完全擦除该斜率。我们得出的结论是，光谱参数的金属性低于-1.5 DEX是错误的，对于这些红色巨型恒星的光度温度和重力应被采用。我们提供了一个简单的关系，以校正光谱温度，以使其置于光度尺度上。
We analysed red giant branch stars in 16 Galactic globular clusters, computing their atmospheric parameters both from the photometry and from excitation and ionisation balances. The spectroscopic parameters are lower than the photometric ones and this discrepancy increases decreasing the metallicity, reaching, at [Fe/H]~-2.5 dex, differences of ~350 K in effective temperature and ~1 dex in surface gravity. We demonstrate that the spectroscopic parameters are inconsistent with the position of the stars in the colour-magnitude diagram, providing too low temperatures and gravities, and predicting that the stars are up to about 2.5 magnitudes brighter than the observed magnitudes. The parameter discrepancy is likely due to the inadequacies of the adopted physics, in particular the assumption of 1-dimensional geometry can be the origin of the observed slope between iron abundances and excitation potential that leads to low temperatures. However, the current modelling of 3D/NLTE radiative transfer for giant stars seems to be not able to totally erase this slope. We conclude that the spectroscopic parameters are wrong for metallicity lower than -1.5 dex and for these red giant stars photometric temperatures and gravities should be adopted. We provide a simple relation to correct the spectroscopic temperatures in order to put them onto a photometric scale.
