Study of HST counterparts to Chandra X-ray sources in the Globular Cluster M71

Hsiu-Hui Huang (MPE, GERMANY) , Werner Becker (MPE, Germany), Bau-Ching Hsieh (ASIAA, Taiwan), Ronald Elsner (MSFC, USA), Peter Edmonds (SAO, USA), et al.

We report on the archival Hubble Space Telescope (HST) observations of the globular cluster M71 (NGC 6838). Those observations which cover the core of the globular cluster are performed by the Advanced Camera for Surveys (ACS) and the Wide Field Planetary Camera 2 (WFPC2). Inside the half-mass radius (r_h =1.65') of M71, 29 X-ray sources have been detected by the Chandra Observations (Elsner et al. 2007) in the energy range of 0.3 - 8.0 keV, and 5 of which lie within one core radius (r_c =0.63') from the cluster center. We find 26 candidate optical counterparts to Chandra X-ray sources inside the half-mass radius of M71. Based on the X-ray and optical properties of the identifications, candidates of cataclysmic variables(CVs), chromospherically active binaries (ABs), and background galaxies located along the line of sight to M71 are classified in our research.