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

Abstract

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.

arXiv comment25 pages, 7 figures. Accepted for publication in The Astronomical Journal

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• The Spectra and Variability of X-ray Sources in a Deep Chandra Observation of the Galactic Center
• Stellar coronal astronomy - a review
• XMM-Newton and the Pleiades -- I: Bright coronal sources and the X-ray emission from intermediate-type stars
• X-ray Properties of Young Stellar Objects in OMC-2 and OMC-3 from the Chandra X-ray Observatory
• Chandra X-ray observations of Young Clusters I. NGC2264 Data
• Chandra Observations of the Pleiades Open Cluster: X-ray Emission from Late-B to Early-F Type Binaries