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

We present results from a 36 ks observation of the core of the Pleiades ope n cluster using ACIS-I on the Chandra X-Ray Observatory. We have detected 5 7 sources, most of which do not have previously known optical counterparts. Follow-up photometry indicates that many of the detections are likely to b e active galactic nuclei, in accordance with extragalactic source counts, b ut some of the sources may be previously undiscovered low-mass members of t he Pleiades. We discuss our data set 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 Pl eiades B6 IV-F4 V stars suggest a tentative conclusion that Pleiades stars in this spectral type range are intrinsic X-ray sources rather than previou sly unknown binaries in which the X-ray emission is from a late-type compan ion. Also, the sensitivity of Chandra allowed us to detect nonflare X-ray e mission from late M stars.