The Pre-He White Dwarf in the Post-mass Transfer Binary EL CVn
The Pre-He White Dwarf in the Post-mass Transfer Binary EL CVn
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DOI：
10.3847/1538-3881/ab52fa
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发表时间：
2019-12
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通讯作者：
Luqian 璐茜 Wang 王;D. Gies;K. Lester;Zhao Guo;R. Matson;G. Peters;V. Dhillon;T. Butterley;S. Li
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作者：
Luqian 璐茜 Wang 王;D. Gies;K. Lester;Zhao Guo;R. Matson;G. Peters;V. Dhillon;T. Butterley;S. Li
EL CVn是一类食双星的原型，由一颗A型或F型主序星星星和一颗热的低质量前氦白色矮星（前氦WD）组成，后者是前质量供体的剥离残骸。在这里，我们提出了第一个直接检测和表征的光谱前，他WD在EL CVn，这是通过远紫外光谱与哈勃太空望远镜宇宙起源光谱仪。这些光谱跨越的波长范围内的流量优势转移前，他WD的A星星。这两个组成部分的径向速度是从远紫外光谱和新的光谱从阿帕奇点天文台天体物理研究联合会Echelle摄谱仪测量。我们还获得了快节奏测光的日食与pt 5米望远镜在罗克德洛斯Muchachos天文台。对速度和光变曲线的综合分析得出了组分的质量和半径。我们应用多普勒层析成像算法来重建各个光谱，并将其与模型进行比较，以估计有效温度。前He WD质量低（0.176 ± 0.004 M），体积小（0.284 ± 0.003 R），温度相对较高（11，800 ± 400 K），这些参数与通过稳定质量转移剥离的星星的预测大致一致。的光谱线的前，他WD表明，它的气氛是H-丰富的，He-贫化，和贫金属，可能是由于元素扩散，已发生的质量转移停止。
EL CVn is the prototype of a class of eclipsing binaries that consist of an A- or F-type main-sequence star and a hot, low-mass, pre-He white dwarf (pre-He WD), the stripped down remains of the former mass donor. Here we present the first direct detection and characterization of the spectrum of the pre-He WD in EL CVn that was made possible through far-UV spectroscopy with the Hubble Space Telescope Cosmic Origins Spectrograph. These spectra straddle the wavelength range where flux dominance shifts from the pre-He WD to the A star. Radial velocities of both components were measured from the far-UV spectra and new optical spectra from the Apache Point Observatory Astrophysical Research Consortium Echelle Spectrograph. We also obtained fast cadence photometry of the eclipses with the pt5m telescope at the Roque de los Muchachos Observatory. A combined analysis of the velocities and light curve yields the component masses and radii. We applied a Doppler tomography algorithm to reconstruct the individual spectra, and we compared these to models to estimate the effective temperatures. The pre-He WD has low mass (0.176 ± 0.004 M⊙), is small (0.284 ± 0.003 R⊙), and is relatively hot (11,800 ± 400 K), and these parameters are approximately consistent with predictions for a star stripped through stable mass transfer. The spectral lines of the pre-He WD show that its atmosphere is H-rich, He-depleted, and metal-poor, probably as the result of elemental diffusion that has occurred since mass transfer ceased.