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arXiv 0811.1508astro-ph
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斯隆数字巡天636个白矮星-M双星的光谱分析

Spectral analysis of 636 white dwarf - M star binaries from the Sloan Digital Sky Survey

René Heller, Derek Homeier, Stefan Dreizler, Roy Østensen

备注：
accepted by A&A October 3, 2008, 15 pages, 16 figures, 3 tables; v2, minor grammatical changes, essential changes in Sect. 5.2
发表信息：
AIP Conf.Proc.1094:931-934,2009; J.Phys.Conf.Ser.172:012023,2009
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摘要：

我们提出了一个857白矮星（WD）-M双星的斯隆数字巡天（SDSS）的第六次数据发布（DR 6），其中大部分是以前确定的目录。对其中的636颗恒星进行了光谱分析，得到了它们的恒星成分和离地距离的基本参数。我们试图通过完成光谱分析来测量这些系统的基本参数。我们使用卡方最小化技术来分解每个组合谱，并推导出其分量的独立参数估计。我们的光谱样本中的41个恒星二重奏在各自的SDSS图像中得到了光学分辨。对于这些系统，我们还推导出了它们的最小真实空间间隔和轨道周期的下限，通常约为10^4年。光谱的167恒星二重奏显示显着的氢排放，在大多数情况下没有额外的He i或He ii功能。我们还发现636个WD中有20个符合DO，其中16个测量的T_eff约为40，000 K。此外，我们确定了70个非常低质量的物体，这些物体的质量小于约0.1太阳质量，是候选的亚恒星同伴。虽然各种选择效应可能起作用，但轨道间距约为500 AU的WD-M双星的比例为6.4%，这是双星系统演化模型的标准。活跃的M矮星可能存在于155个巴耳末发射系统中，占24.4%。过多的冷DO最有可能是由于DB-DO T_eff范围内的额外WD，对此没有完成详细的拟合。M星比WD分量更接近地球的趋势可能是由于低估了理论上的M星半径。

英文摘要：

We present a catalog of 857 white dwarf (WD)-M binaries from the sixth data release (DR6) of the Sloan Digital Sky Survey (SDSS), most of which were previously identified. For 636 of them, we complete a spectral analysis and derive the basic parameters of their stellar constituents and their distances from Earth. We attempt to measure fundamental parameters of these systems by completing spectral analyses. We use a Chi^2 minimization technique to decompose each combined spectrum and derive independent parameter estimates for its components. Forty-one of the stellar duets in our spectroscopic sample are optically resolved in their respective SDSS images. For these systems, we also derive a minimum true spatial separation and a lower limit to their orbital periods, typically which are some 10^4 yr. Spectra of 167 stellar duets show significant hydrogen emission and in most cases no additional He i or He ii features. We also find that 20 of the 636 WDs are fitted to be DOs, with 16 measured to have T_eff around 40,000 K. Furthermore, we identify 70 very low-mass objects, which are secondaries of masses smaller than about 0.1 solar masses, to be candidate substellar companions. Although various selection effects may play a role, the fraction 6.4 % of WD-M star binaries with orbital separations of around 500 AU is a criterion for evolutionary models of stellar binary systems. Active M dwarfs are likely present in 155 Balmer-emitting systems, corresponding to a fraction of 24.4 %. The excess of cool DOs is most likely due to additional WDs in the DB-DO T_eff range, for which no detailed fitting was completed. The trend of the M stars being closer to Earth than the WD component is probably due to an underestimation of the theoretical M star radii.

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