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arXiv 1406.6451astro-ph.SR
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银河系隆起白矮星冷却序列的首次探测

First Detection of the White-Dwarf Cooling Sequence of the Galactic Bulge

A. Calamida, K. C. Sahu, J. Anderson, S. Casertano, S. Cassisi, M. Salaris, T. Brown, J. Sokol, H. E. Bond, I. Ferraro, H. Ferguson, M. Livio, J. Valenti, R. Bu… 展开作者

A. Calamida, K. C. Sahu, J. Anderson, S. Casertano, S. Cassisi, M. Salaris, T. Brown, J. Sokol, H. E. Bond, I. Ferraro, H. Ferguson, M. Livio, J. Valenti, R. Buonanno, W. Clarkson, A. Pietrinferni

摘要:

我们目前的哈勃太空望远镜数据的低变红人马座窗口在银河系的隆起。在F606 W和F814 W过滤器中观测了人马座窗口扫描太阳系外行星搜索场(3 'x3'),以及另外三个高级巡天照相机和八个宽视场照相机3场,大约每两周观测一次,持续两年,主要目的是通过天体测量微透镜探测隐藏的孤立黑洞和中子星群。在F606 W ~25.5等的两个轴上,自行的测量精度为~0.1 mas/yr(~4 km/s),在F606 W ~28等的两个轴上,自行的测量精度优于~0.5 mas/yr(20 km/s)。自行测量使我们能够分离盘星和核球星,并获得一个清晰的核球色星等图。然后,我们第一次确定了银河系隆起中的一个白矮星(WD)冷却序列,以及十几个候选的极端水平分支恒星。理论和观测结果之间的比较表明,相当一部分的WD(30%)是系统红比CO核心富氢和氦丰富的信封WD的冷却轨道。这一证据表明,在隆起中存在着大量的低质量WD和WD -主序星双星。两颗爆发的矮新星、两颗短周期(P <1d)椭球变星和几颗候选激变变星的发现进一步支持了这一假说。

英文摘要:

We present Hubble Space Telescope data of the low-reddening Sagittarius window in the Galactic bulge. The Sagittarius Window Eclipsing Extrasolar Planet Search field (3'x3'), together with three more Advanced Camera for Surveys and eight Wide Field Camera 3 fields, were observed in the F606W and F814W filters, approximately every two weeks for two years, with the principal aim of detecting a hidden population of isolated black holes and neutron stars through astrometric microlensing. Proper motions were measured with an accuracy of ~0.1 mas/yr (~4 km/s) at F606W~25.5 mag, and better than ~0.5 mas/yr (20 km/s) at F606W~28 mag, in both axes. Proper-motion measurements allowed us to separate disk and bulge stars and obtain a clean bulge color-magnitude diagram. We then identified for the first time a white dwarf (WD) cooling sequence in the Galactic bulge, together with a dozen candidate extreme horizontal branch stars. The comparison between theory and observations shows that a substantial fraction of the WDs (30%) are systematically redder than the cooling tracks for CO-core H-rich and He-rich envelope WDs. This evidence would suggest the presence of a significant number of low-mass WDs and WD - main sequence binaries in the bulge. This hypothesis is further supported by the finding of two dwarf novae in outburst, two short-period (P < 1 d) ellipsoidal variables, and a few candidate cataclysmic variables in the same field.

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