An Unexpected Discovery in the Rich Open Cluster NGC 6819 Using XMM-Newton
Abstract
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 1030 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.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- January 2012
- DOI:
- 10.1088/0004-637X/745/1/57
- arXiv:
- arXiv:1111.6589
- Bibcode:
- 2012ApJ...745...57G
- Keywords:
-
- binaries: close;
- open clusters and associations: individual: NGC 6819;
- X-rays: binaries;
- Astrophysics - Solar and Stellar Astrophysics
- E-Print:
- 14 pages, 11 figures, accepted for publication in the Astrophysical Journal