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首页> 外文期刊>The Astrophysical journal >COOL WHITE DWARFS REVISITED: NEW SPECTROSCOPY AND PHOTOMETRY
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COOL WHITE DWARFS REVISITED: NEW SPECTROSCOPY AND PHOTOMETRY

机译：修改过的冷白矮人：新光谱学和分光光度法

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In this paper we present new and improved data on 38 cool white dwarfs identified in 2001 by Oppenheimer and coworkers as candidate dark-halo objects. Using the high-resolution spectra obtained with LRIS on Keck I, we measure precise radial velocities for 13 white dwarfs that show an Hα absorption line. We show that accounting for radial velocities on average decreases the U-V plane velocities by only 6%. In two cases, accounting for the radial velocities put original halo candidates below the Oppenheimer and coworkers velocity cut. The radial velocity sample has a velocity dispersion in the direction perpendicular to the Galactic plane of σ_W = 59 km s~(-1), between the values typically associated with the thick-disk and stellar-halo populations. We also see indications of the presence of two populations by analyzing the velocities in the U-V plane. In addition, we present CCD photometry for half of the sample, and with it recalibrate the photographic photometry of the remaining white dwarfs. Using the new photometry in standard bands and applying the appropriate color-magnitude relations for hydrogen and helium atmospheres, we obtain new distance estimates. By recalibrating the distances of the white dwarfs that were not originally selected as halo candidates, we obtain 13 new candidates (and lose two original ones). On average, the new distances produce velocities in the U-V plans that are larger by 10%, with already fast objects gaining more. Using the new data while applying the same U-V plane velocity cut (94 km s~(-1)) and methods of analysis as did Oppenheimer and coworkers, we find a density of cool white dwarfs of 1.7 x 10~(-4) pc~(-3), confirming their value. In addition, we derive the density as a function of the U-V plane velocity cutoff. The density (corrected for losses due to higher U-V plane velocity cuts) starts to flatten out at 150 km s~(-1) (0.4 x 10~(-4) pc~(-3)) and is minimized (thus minimizing the possible nonhalo contamination) at 190 km s~(-1) (0.3 x 10~(-4) pc~(-3)). These densities are in rough agreement with the estimates for the stellar-halo white dwarfs, corresponding to values a factor of 1.9 and 1.4 higher.
机译：在本文中，我们介绍了2001年由Oppenheimer和其同事确定为候选暗晕物体的38个冷白矮星的新数据和改进后的数据。使用在Keck I上通过LRIS获得的高分辨率光谱，我们测量了显示Hα吸收线的13个白矮星的精确径向速度。我们表明，平均考虑径向速度会使U-V平面速度仅降低6％。在两种情况下，考虑到径向速度，原始光晕候选物位于Oppenheimer和同事的速度削减之下。径向速度样本在垂直于银河平面的方向上的速度分散为σ_W= 59 km s〜（-1），介于通常与厚盘和恒星-晕圈种群相关的值之间。通过分析U-V平面中的速度，我们还可以看到存在两个种群的迹象。此外，我们介绍了一半样品的CCD光度法，并用它重新校准了剩余白矮星的光度法。在标准波段中使用新的测光法，并对氢气和氦气气氛应用适当的色度关系，我们可以获得新的距离估算值。通过重新校准最初未被选为光晕候选者的白矮星的距离，我们获得了13个新候选者（并丢失了两个原始候选者）。平均而言，新距离在U-V计划中产生的速度要大10％，而已经很快的物体会获得更多的速度。使用新数据，同时应用与Oppenheimer及其同事相同的UV平面速度切线（94 km s〜（-1））和分析方法，我们发现冷白矮星的密度为1.7 x 10〜（-4）pc 〜（-3），确认其值。另外，我们得出密度是U-V平面速度截止的函数。在150 km s〜（-1）（0.4 x 10〜（-4）pc〜（-3））时，密度（已校正因较高的UV平面速度削减造成的损失）开始趋于平坦，从而使其最小化（因此将190 km s〜（-1）（0.3 x 10〜（-4）pc〜（-3））。这些密度与恒星-晕白矮星的估计值大致吻合，对应的值分别高1.9和1.4。

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