arXiv 0704.03552007-04-03astro-ph

高速晕白矮星候选者的三角视差

Trigonometric parallaxes of high velocity halo white dwarf candidates

C. Ducourant, R. Teixeira, N. C. Hambly, B. R. Oppenheimer, M. R. S. Hawkins, M. Rapaport, J. Modolo, J. F. Lecampion

DOI：: 10.1051/0004-6361:20066876

摘要：

Oppenheimer等人（2001）确认的38颗晕白矮星候选者的状态已经被许多作者深入讨论。在迄今为止进行的分析中，三角函数松弛是关键的缺失数据。距离测量是强制性的运动学隔离晕对象从磁盘对象，从而使一个更可靠的估计晕暗物质驻留在这样的对象的局部密度。我们从Oppenheimer等人（2001）的名单中选出15颗候选晕白矮星（WD），给出了它们的三角视差测量结果。从2001年8月到2004年7月，我们使用ESO 1.56米丹麦望远镜和ESO 2.2米望远镜观测了这些恒星。视差的精度为1- 2 mas的确定产生的相对误差$\sim5$ %的距离为6个对象，$\sim12$ %的3个对象，和$\sim20$ %的两个以上的对象。在我们的观测中，四颗恒星似乎太遥远了（可能比100 pc更远），无法测量它们的视差。从Oppenheimer等人（2001年）的列表中推导出了15个晕WD的距离、绝对星等和修正的空间速度。Halo成员资格被明确地确认为6个对象，而5个对象可能是厚盘成员，4个对象太远，无法仅根据运动学得出任何结论。将我们的三角测量与以前工作中使用的光度测量进行比较，发现从光度测量技术中得出的距离估计过高。这个新的数据集可以用来修正晕白矮星的空间密度，分析结果将在随后的出版物中发表。

英文摘要：

The status of 38 halo white dwarf candidates identified by Oppenheimer et al. (2001) has been intensively discussed by various authors. In analyses undertaken to date, trigonometric parallaxes are crucial missing data. Distance measurements are mandatory to kinematically segregate halo object from disk objects and hence enable a more reliable estimate of the local density of halo dark matter residing in such objects. We present trigonometric parallax measurements for 15 candidate halo white dwarfs (WDs) selected from the Oppenheimer et al. (2001) list. We observed the stars using the ESO 1.56-m Danish Telescope and ESO 2.2-m telescope from August 2001 to July 2004. Parallaxes with accuracies of 1--2 mas were determined yielding relative errors on distances of $\sim5$% for 6 objects, $\sim12$% for 3 objects, and $\sim20$% for two more objects. Four stars appear to be too distant (probably farther than 100 pc) to have measurable parallaxes in our observations. Distances, absolute magnitudes and revised space velocities were derived for the 15 halo WDs from the Oppenheimer et al. (2001) list. Halo membership is confirmed unambiguously for 6 objects while 5 objects may be thick disk members and 4 objects are too distant to draw any conclusion based solely on kinematics. Comparing our trigonometric parallaxes with photometric parallaxes used in previous work reveals an overestimation of distance as derived from photometric techniques. This new data set can be used to revise the halo white dwarf space density, and that analysis will be presented in a subsequent publication.

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