标题： 利用钱德拉X射线天文台对昂宿星团核心的观测 显示英文标题

标题： Observations of the core of the Pleiades with the Chandra X-ray Observatory

摘要： 我们展示了利用钱德拉X射线天文台的ACIS-I对昂宿星团核心进行一次36千秒观测所获得的结果。我们探测到了57个源，其中大多数之前没有已知的光学对应体。后续的测光表明，许多探测结果很可能是AGN，这与河外源计数一致，但其中一些源可能是之前未发现的昂宿星团低质量成员。我们讨论了我们的数据集以及关于早期型恒星和极晚期型恒星X射线辐射的研究成果。特别是，四个昂宿星团B6 IV - F4 V型恒星的大X射线流量、无变异性以及硬度比表明，这一光谱类型范围内的昂宿星团恒星很可能是固有的X射线源，而不是之前未知的由晚期型伴星产生X射线辐射的双星系统。此外，钱德拉望远镜的灵敏度使我们能够探测到晚期M型恒星的非耀发X射线辐射。 显示英文摘要

摘要： We present results from a 36-ksec observation of the core of the Pleiades open cluster using ACIS-I on the Chandra X-ray Observatory. We have detected 57 sources, most of which do not have previously known optical counterparts. Follow-up photometry indicates that many of the detections are likely to be AGNs, in accordance with extragalactic source counts, but some of the sources may be previously undiscovered low-mass members of the Pleiades. We discuss our dataset and our findings about X-ray emission from early-type stars as well as very late type stars. In particular, the large X-ray fluxes, lack of variability, and hardness ratios of the four Pleiades B6 IV -- F4 V stars suggest a tentative conclusion that Pleiades stars in this spectral type range are intrinsic X-ray sources rather than previously unknown binaries in which the X-ray emission is from a late-type companion. Also the sensitivity of Chandra allowed us to detect nonflare X-ray emission from late-M stars.