An Unexpected Discovery In The Rich Open Cluster NGC 6819 Using XMM-Newton




Gosnell, Natalie M.
Pooley, David
Geller, Aaron M.
Kalirai, Jason
Mathieu, Robert D.
Frinchaboy, Peter
Ramirez-Ruiz, Enrico

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We present the first study of the X-ray population of the intermediate-age rich open cluster NGC 6819 using the XMM-Newton Observatory. In the past decade, Chandra X-ray observations have shown a relationship between the X-ray population of globular clusters and their internal dynamics and encounter frequency. We investigate the role dynamics possibly play in the formation of X-ray sources in NGC 6819, and compare our results with known properties of field and globular cluster X-ray populations. We implement a multi-wavelength approach to studying the X-ray sources, utilizing X-ray and UV data from XMM observations along with the wealth of photometry and radial-velocity data from the WIYN Open Cluster Study and the CFHT Open Cluster Survey. Within the cluster half-light radius, we detect 12 X-ray sources down to a luminosity of 10(30) erg s(-1) for cluster members. The sources include a candidate quiescent low-mass X-ray binary (qLMXB), a candidate cataclysmic variable, and two active binary systems. The presence of a qLMXB in an open cluster is previously unexpected given the known relationships between luminous X-ray sources and encounter frequency in globular clusters, and most likely has a dynamical origin.



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Gosnell, Natalie M., David Pooley, Aaron M. Geller, Jason Kalirai, Robert D. Mathieu, Peter Frinchaboy, and Enrico Ramirez-Ruiz. "An Unexpected Discovery in the Rich Open Cluster NGC 6819 Using XMM-Newton." The Astrophysical Journal, Vol. 745, No. 1 (Jan., 2012): 57.