X-Ray Detection of the Cluster Containing the Cepheid S Mus
Schaefer, Gail H.; Bond, Howard E.; Evans, Nancy Remage; Karovska, Margarita; Guinan, Edward; Engle, Scott; Pillitteri, Ignazio; Wolk, Scott; Tingle, Evan; DePasquale, Joseph
United States, Italy
Abstract
The galactic Cepheid S Muscae has recently been added to the important list of Cepheids linked to open clusters, in this case the sparse young cluster ASCC 69. Low-mass members of a young cluster are expected to have rapid rotation and X-ray activity, making X-ray emission an excellent way to discriminate them from old field stars. We have made an XMM-Newton observation centered on S Mus and identified a population of X-ray sources whose near-IR Two Micron All Sky Survey counterparts lie at locations in the J, (J - K) color-magnitude diagram consistent with cluster membership at the distance of S Mus. Their median energy and X-ray luminosity are consistent with young cluster members as distinct from field stars. These strengthen the association of S Mus with the young cluster, making it a potential Leavitt law (period-luminosity relation) calibrator.