Settling onto the Main Sequence:ROSATObservations ofh and χ Persei

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Abstract
We have studied X-rays from the double cluster h and χ Per with an 11 ks ROSAT position-sensitive proportional counter (PSPC) observation. Emission is concentrated toward the two cluster centers. Whether the emission is diffuse emission or from a population of unresolved faint sources is uncertain because the resolution is poor at the distance of the clusters (2.4 kpc). Twenty-three sources were found with an X-ray luminosity of log L = 31.5 ergs s-1 or greater. These sources were found in the cluster nuclei, between the clusters, and in a halo around the cluster pair. The ROSAT PSPC error circle is too large for the identification of X-ray sources with individual optical objects. However, because of a lack of correlation between X-ray sources and B stars, we conclude that the X-rays are produced by late spectral type pre-main-sequence stars. The X-ray sources are brighter than all but the very brightest sources in the younger Orion Nebula cluster, which makes them important in tracing the final stages approaching the main sequence.

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