中间极性EX Hydrae的高分辨率光谱。I.运动学研究和Roche层析成像
High-resolution spectroscopy of the intermediate polar EX Hydrae. I. Kinematic study and Roche tomography
摘要：
EX Hya是少数几个双线食激变变星之一，可以精确测量双星的质量。我们分析了轨道相位分辨UVES/ VLT高分辨率光谱观测EX Hya的目的是推导出的二进制质量和获得的照明二级星的断层图像。我们提出了一种新的方法，用于确定的二元参数直接拟合的发光二级星的相位分辨线轮廓的吸收和发射的NaI λ 8183/ 8195和CaII λ 8498发射的发射模型。对NaI和CaII的线轮廓的拟合，结合已发表的K1，得到白矮星的质量M1 = 0.790 +/- 0.026 Msun，次级质量M2 = 0.108 +/- 0.008 Msun，次级恒星的速度振幅K2 = 432.4 +/- 4.8 km s-1。次级恒星的光谱类型为dM5.5 +/- 0.5，K波段绝对星等为MK = 8.8。它的洛希半径使它位于或非常接近低质量恒星的主序星。它与主序星的不同之处在于它有一个面向白矮星的被照亮的半球。在7500埃，次级恒星对观测到的自旋相平均通量的贡献只有5%，在8200埃，只有7.5%，在K波段，只有37%。我们目前的图像中的第二颗星的光的NaI双重和CaII发射线与简化版本的罗氏层析成像。我们发现了EX Hya中第二颗恒星的窄谱线，这些谱线描绘了它的轨道运动，使我们能够得出两个组成部分的精确质量。主要质量明显超过最近公布的值。次级恒星是一颗低质量的主序星，在其明亮的一侧显示出丰富的发射线光谱，但在其黑暗的一侧缺乏色球发射。
英文摘要：
EX Hya is one of the few double-lined eclipsing cataclysmic variables that allow an accurate measurement of the binary masses. We analyze orbital phase-resolved UVES/ VLT high resolution spectroscopic observations of EX Hya with the aims of deriving the binary masses and obtaining a tomographic image of the illuminated secondary star. We present a novel method for determining the binary parameters by directly fitting an emission model of the illuminated secondary star to the phase-resolved line profiles of NaI lambda 8183/ 8195 in absorption and emission and CaII lambda 8498 in emission. The fit to the NaI and CaII line profiles, combined with the published K1, yields a white-dwarf mass M1 = 0.790 +/- 0.026 Msun, a secondary mass M2 = 0.108 +/- 0.008 Msun, and a velocity amplitude of the secondary star K2 = 432.4 +/- 4.8 km s-1. The secondary is of spectral type dM5.5 +/- 0.5 and has an absolute K-band magnitude of MK = 8.8. Its Roche radius places it on or very close to the main sequence of low-mass stars. It differs from a main sequence star by its illuminated hemisphere that faces the white dwarf. The secondary star contributes only 5% to the observed spin-phase averaged flux at 7500 A, 7.5% at 8200 A, and 37% in the K-band. We present images of the secondary star in the light of the NaI doublet and the CaII emission line derived with a simplified version of Roche tomography. We have discovered narrow spectral lines from the secondary star in EX Hya that delineate its orbital motion and allow us to derive accurate masses of both components. The primary mass significantly exceeds recently published values. The secondary is a low-mass main sequence star that displays a rich emission line spectrum on its illuminated side, but lacks chromospheric emission on its dark side.
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