X射线爆发中子星大气模型：光谱和颜色校正
X-ray bursting neutron star atmosphere models: spectra and color corrections
摘要：
低质量X射线双星中的X射线爆发中子星构成了一个合适的源类，以限制质量和半径的中子星，但足够扩展的一套相应的模型大气是必要的这些调查。我们计算了这样一组模型的大气和紧急的光谱在一个平面平行，流体静力学，LTE近似康普顿散射考虑。这些模型计算了六种不同的化学成分：纯氢和纯氦大气，以及太阳氢和氦混合的大气，以及各种重元素丰度Z = 1，0.3，0.1和0.01 Z_sun。对于每一种化学成分，计算模型的表面重力的三个值，log g =14.0，14.3，和14.6，并为20个值的光度单位的爱丁顿光度，L/L_Edd，在0.001--0.98范围内。在RXTE/PCA的3- 20 keV能带，对所有模型的出射光谱进行了红移和稀释黑体拟合，并给出了相应的色校正（硬度因子）fc值。理论关系fc-L/L-Edd可以拟合到观测到的X射线暴冷却阶段黑体归一化K与通量的关系K^{-1/4} - F，从而确定爱丁顿通量和视中子星半径与源距的比值。在已知距离的情况下，这些参数可以转化为对中子星质量和半径的约束。理论大气谱也可用于与观测到的X射线暴谱进行直接比较。
英文摘要：
X-ray bursting neutron stars in low mass X-ray binaries constitute an appropriate source class to constrain masses and radii of neutron stars, but a sufficiently extended set of corresponding model atmospheres is necessary for these investigations. We computed such a set of model atmospheres and emergent spectra in a plane-parallel, hydrostatic, and LTE approximation with Compton scattering taken into account. The models were calculated for six different chemical compositions: pure hydrogen and pure helium atmospheres, and atmospheres with solar mix of hydrogen and helium, and various heavy element abundances Z = 1, 0.3, 0.1, and 0.01 Z_sun. For each chemical composition the models are computed for three values of surface gravity, log g =14.0, 14.3, and 14.6, and for 20 values of the luminosity in units of the Eddington luminosity, L/L_Edd, in the range 0.001--0.98. The emergent spectra of all models are redshifted and fitted by a diluted blackbody in the RXTE/PCA 3--20 keV energy band, and corresponding values of the color correction (hardness factors) f_c are presented. Theoretical dependences f_c - L/L_Edd can fitted to the observed dependence K^{-1/4} - F of the blackbody normalization K on flux during cooling stages of X-ray bursts to determine the Eddington flux and the ratio of the apparent neutron star radius to the source distance. If the distance is known, these parameters can be transformed to the constraints on neutron star mass and radius. The theoretical atmosphere spectra can also be used for direct comparison with the observed X-ray burst spectra.
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