Issue |
A&A
Volume 445, Number 1, January I 2006
|
|
---|---|---|
Page(s) | 155 - 165 | |
Section | Galactic structure, stellar clusters, and populations | |
DOI | https://doi.org/10.1051/0004-6361:20053010 | |
Published online | 13 December 2005 |
XMM-Newton X-ray and optical observations of the globular clusters M 55 and NGC 3201
1
Centre d'Étude Spatiale des Rayonnements, 9 avenue du Colonel Roche, 31028 Toulouse Cedex 04, France e-mail: Natalie.Webb@cesr.fr
2
Department of Physics and Astronomy, University of Leicester, Leicester LE1 7RH, UK
Received:
7
March
2005
Accepted:
31
August
2005
We have observed two low concentration Galactic globular
clusters with the X-ray observatory XMM-Newton. We detect 47
faint X-ray sources in the direction of M 55 and 62 in the
field of view of NGC 3201. Using the statistical
Log N - Log S relationship of extragalactic sources derived from XMM-Newton Lockman Hole observations, to estimate the background
source population, we estimate that very few of the sources
() in the field of view of M 55 actually belong
to the cluster. These sources are located in the centre of the
cluster as we expect if the cluster has undergone mass
segregation. NGC 3201 has approximately 15 related
sources, which are centrally located but are not constrained to lie
within the half mass radius. The sources belonging to this cluster
can lie up to 5 core radii from the centre of the cluster which
could imply that this cluster has been perturbed. Using X-ray (and
optical, in the case of M 55) colours, spectral and timing
analysis (where possible) and comparing these observations to
previous X-ray observations, we find evidence for sources in each
cluster that could be cataclysmic variables, active binaries,
millisecond pulsars and possible evidence for a quiescent low mass
X-ray binary with a neutron star primary, even though we do not
expect any such objects in either of the clusters, due to their low
central concentrations. The majority of the other sources are
background sources, such as AGN.
Key words: Galaxy: globular clusters: individual: M 55, NGC 3201 / X-rays: general / stars: binaries: general / stars: variables: general
© ESO, 2005
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