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A New Analysis of RR Lyrae Kinematics in the Solar Neighborhood

机译:太阳近邻RR天琴运动学的新分析

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Full space velocities are computed for a sample of 130 nearby RR Lyrae variables using both ground-based and Hipparcos proper motions. In many cases proper motions for the same star from multiple sources have been averaged to produce approximately a factor of 2 improvement in the transverse space velocity errors. In most cases, this exceeds the accuracy attained using Hipparcos proper motions alone. The velocity ellipsoids computed for halo and thick-disk samples are in agreement with those reported in previous studies. A distinct sample of thin-disk RR Lyrae variables has not been isolated, but there is kinematic evidence for some thin-disk contamination in our thick-disk samples. Using kinematic and spatial parameters, a sample of 21 stars with [Fe/H] < -1.0 and disklike kinematics have been isolated. From their kinematics and spatial distribution we conclude that these stars represent a sample of RR Lyrae variables in the metal-weak tail of the thick disk that extends to [Fe/H] = -2.05. In the halo samples, the distribution of V velocities is not Gaussian, even when the metal-weak thick-disk stars are removed. Possibly related, a plot of U and W velocities as a function of V velocity for the kinematically unbiased halo sample shows some curious structure. The cause of these kinematic anomalies is not clear. In addition, systematic changes to the distance scale within the range of currently accepted values of Mv(RR) are shown to significantly change the calculated halo kinematics. Fainter values of Mv(RR), such as those obtained by statistical parallax (~0.60 to 0.70 at [Fe/H] = -1.9), result in local halo kinematics similar to those reported in independent studies of halo kinematics, while brighter values of Mv(RR), such as those obtained through recent analysis of Hipparcos subdwarf parallaxes (~0.30 to 0.40 at [Fe/H] = -1.9), result in a halo with retrograde rotation and significantly enlarged velocity dispersions.
机译:使用基于地面的运动和Hipparcos的适当运动,为130个附近的RR Lyrae变量的样本计算了全空间速度。在许多情况下,已对来自多个源的同一颗恒星的适当运动进行了平均,以使横向空速误差提高大约2倍。在大多数情况下,这超出了仅使用Hipparcos适当运动所能达到的精度。为晕圈和厚盘样品计算的速度椭球与先前研究中报道的一致。尚未分离出稀疏磁盘RR Lyrae变量的独特样本,但是有运动学证据表明我们的厚磁盘样本中存在一些稀磁盘污染。使用运动学和空间参数,已分离出[Fe / H] <-1.0的21个恒星样本和盘状运动学。根据它们的运动学和空间分布,我们得出结论,这些恒星代表厚盘金属弱尾部的RR Lyrae变量样本,延伸至[Fe / H] = -2.05。在晕圈样本中,即使去除了金属弱的厚盘星,V速度的分布也不是高斯分布。可能相关的是,运动学上无偏的晕圈样本的U和W速度与V速度的函数关系图显示出一些奇怪的结构。这些运动异常的原因尚不清楚。此外,在当前接受的Mv(RR)值范围内,距离标尺的系统变化显示出会显着改变计算出的光晕运动学。 Mv(RR)的较弱值,例如通过统计视差获得的值(在[Fe / H] = -1.9时约为0.60至0.70),其结果类似于局部运动学中独立的晕轮运动,而较亮的值Mv(RR)的变化,例如最近对Hipparcos亚矮视差(在[Fe / H] = -1.9时约为0.30至0.40)进行分析所获得的那些,会导致光晕逆行旋转并显着增大速度分散度。

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