Volume 513, April 2010
|Number of page(s)||11|
|Section||Galactic structure, stellar clusters, and populations|
|Published online||15 April 2010|
Study of Hubble Space Telescope counterparts to Chandra X-ray sources in the globular cluster M 71
Max-Planck-Institut für extraterrestrische Physik,
Giessenbachstrasse 1, 85748 Garching, Germany e-mail: firstname.lastname@example.org
2 Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138, USA
3 NASA Marshall Space Flight Center, Huntsville, AL 35812, USA
4 Department of Physics, University of Alberta, Edmonton, Alberta, Canada
5 Institute of Astronomy and Astrophysics, Academia Sinica, Taipei 10617, Taiwan
Accepted: 2 December 2009
Aims. We report on archival Hubble Space Telescope (HST) observations of the globular cluster M 71 (NGC 6838).
Methods. These observations, covering the core of the globular cluster, were performed by the Advanced Camera for Surveys (ACS) and the Wide Field Planetary Camera 2 (WFPC2). Inside the half-mass radius (rh = 165) of M 71, we find 33 candidate optical counterparts to 25 out of 29 Chandra X-ray sources, while 6 possible optical counterparts to 4 X-ray sources are found outside the half-mass radius.
Results. Based on the X-ray and optical properties of the identifications, we find 1 certain and 7 candidate cataclysmic variables (CVs). We also classify 2 X-ray sources as certain and 12 as potential chromospherically active binaries (ABs), respectively. The only star in the error circle of the known millisecond pulsar (MSP) is inconsistent with being the optical counterpart.
Conclusions. The number of X-ray faint sources with > 4×1030 erg s-1 (0.5–6.0 keV) found in M 71 is higher than extrapolations from other clusters on the basis of either collision frequency or mass. Since the core density of M 71 is relatively low, we suggest that those CVs and ABs are primordial in origin.
Key words: globular clusters: individual: M 71 globular clusters: individual: NGC 6838
© ESO, 2010
Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.
Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.
Initial download of the metrics may take a while.