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arXiv 0810.3651astro-ph
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来自银河系中心的古老超高速恒星：来自SDSS的极限

Old-Population Hypervelocity Stars from the Galactic Center: Limits from the SDSS

Juna A. Kollmeier, Andrew Gould, Gillian Knapp, Timothy C. Beers

备注：
Submitted to ApJ; 14 pages including 2 figures
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摘要：

我们提出了从SDSS中选出的超过290，000颗恒星的样本中对老年人口HVS的喷射限制。我们推导出在太阳圈的速度从测量的位置和径向速度假设径向轨道，并采用一个简单的等温模型的星系晕，这使我们能够识别候选人绑定和未绑定的弹射器。我们从这个样本中找到了4颗候选的束缚F星，它们都具有负的银河系中心径向速度（即，返回GC）。我们还发现了2颗候选的未绑定恒星（一颗F星和一颗G星），然而，现有的自行测量使这些恒星不太可能从GC中出现。这些数据将老星族恒星从GC中的抛射速率的上限设定为约45/Myr。与质量更大的B星抛射体的速度约为0.5/Myr相比，我们对老人口HVS抛射速度的限制表明GC的质量函数不是底部重的，并且与正常一致。未来对老年人HVS的有针对性的调查可以确定它是否确实头重脚轻。

英文摘要：

We present limits on the ejection of old-population HVS from a sample of over 290,000 stars selected from the SDSS. We derive the speed at the solar circle from the measured positions and radial velocities by assuming a radial orbit and adopting a simple isothermal model of the Galactic halo, which enables us to identify candidate bound and unbound ejectees. We find 4 candidate bound F-stars from this sample, all with negative Galactocentric radial velocity (i.e., returning toward the GC). We additionally find 2 candidate unbound stars (one F and one G), however, existing proper motion measurements make these unlikely to be emerging from the GC. These data place an upper limit on the rate of ejection of old-population stars from the GC of ~45/Myr. Comparing to the rate for more massive B-star ejectees of ~0.5/Myr, our limit on the rate of ejection of old-population HVS shows that the mass function at the GC is not bottom-heavy and is consistent with being normal. Future targeted surveys of old-population HVS could determine if it is indeed top-heavy.

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