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Combined Chandra, XMM-Newton, and Hubble space telescope observations of the galactic globular cluster NGC 2808

Combined Chandra, XMM-Newton, and Hubble space telescope observations of the galactic globular cluster NGC 2808
Combined Chandra, XMM-Newton, and Hubble space telescope observations of the galactic globular cluster NGC 2808
Aims: Using new Chandra X-ray observations and existing XMM-Newton X-ray and Hubble far ultraviolet observations, we aim to detect and identify the faint X-ray sources belonging to the Galactic globular cluster NGC 2808 in order to understand their role in the evolution of globular clusters.

Methods: We present a Chandra X-ray observation of the Galactic globular cluster NGC 2808 . We classify the X-ray sources associated with the cluster by analysing their colours and variability. Previous observations with XMM-Newton and far ultraviolet observations with the Hubble Space Telescope are re-investigated to help identify the Chandra sources associated with the cluster. We compare our results to population synthesis models and observations of other Galactic globular clusters.

Results: We detect 113 sources, of which 16 fall inside the half-mass radius of NGC 2808 and are concentrated towards the cluster core. From statistical analysis, these 16 sources are very likely to be linked to the cluster. We detect short-term (1 day) variability in X-rays for 7 sources, of which 2 fall inside the half-mass radius, and long-term (28 months) variability for 10 further sources, of which 2 fall inside the half-mass radius. Ultraviolet counterparts are found for 8 Chandra sources in the core, of which 2 have good matching probabilities and have ultraviolet properties expected for cataclysmic variables.

We find one likely neutron star-quiescent low-mass X-ray binary and 8 cataclysmic variable candidates in the core of NGC 2808 . The other sources are cataclysmic variable candidates, but some could possibly be active binaries or millisecond pulsars. We find a possible deficit of X-ray sources compared to 47 Tuc which could be related to the metallicity content and the complexity of the evolution of NGC 2808 .
globular clusters, individual, NGC 2808, x-rays, general binaries, close novae, cataclysmic variables
0004-6361
641-654
Servillat, M.
d6a403fa-f475-493b-ae95-fa8b544ed567
Dieball, A.
5f595453-aa6b-4067-a3e1-026867fb9f7a
Webb, N. A.
82e56ad6-42d6-4b59-bb5c-5711df40f3c5
Knigge, C.
ac320eec-631a-426e-b2db-717c8bf7857e
Cornelisse, R.
06976a3f-4a05-4c72-8462-7e71b00e7b77
Barret, D.
343cdacd-9683-4f70-910b-6539201daf06
Long, K. S.
839b3509-5ef3-4126-97fa-912e3357d8ef
Shara, M. M.
70d52b90-8ede-49b6-95fe-738e1b9f2ea9
Zurek, D. R.
302ccf4e-b677-4b4e-9c5b-0173981c2919
Servillat, M.
d6a403fa-f475-493b-ae95-fa8b544ed567
Dieball, A.
5f595453-aa6b-4067-a3e1-026867fb9f7a
Webb, N. A.
82e56ad6-42d6-4b59-bb5c-5711df40f3c5
Knigge, C.
ac320eec-631a-426e-b2db-717c8bf7857e
Cornelisse, R.
06976a3f-4a05-4c72-8462-7e71b00e7b77
Barret, D.
343cdacd-9683-4f70-910b-6539201daf06
Long, K. S.
839b3509-5ef3-4126-97fa-912e3357d8ef
Shara, M. M.
70d52b90-8ede-49b6-95fe-738e1b9f2ea9
Zurek, D. R.
302ccf4e-b677-4b4e-9c5b-0173981c2919

Servillat, M., Dieball, A., Webb, N. A., Knigge, C., Cornelisse, R., Barret, D., Long, K. S., Shara, M. M. and Zurek, D. R. (2008) Combined Chandra, XMM-Newton, and Hubble space telescope observations of the galactic globular cluster NGC 2808. Astronomy & Astrophysics, 490 (2), 641-654. (doi:10.1051/0004-6361:200810188).

Record type: Article

Abstract

Aims: Using new Chandra X-ray observations and existing XMM-Newton X-ray and Hubble far ultraviolet observations, we aim to detect and identify the faint X-ray sources belonging to the Galactic globular cluster NGC 2808 in order to understand their role in the evolution of globular clusters.

Methods: We present a Chandra X-ray observation of the Galactic globular cluster NGC 2808 . We classify the X-ray sources associated with the cluster by analysing their colours and variability. Previous observations with XMM-Newton and far ultraviolet observations with the Hubble Space Telescope are re-investigated to help identify the Chandra sources associated with the cluster. We compare our results to population synthesis models and observations of other Galactic globular clusters.

Results: We detect 113 sources, of which 16 fall inside the half-mass radius of NGC 2808 and are concentrated towards the cluster core. From statistical analysis, these 16 sources are very likely to be linked to the cluster. We detect short-term (1 day) variability in X-rays for 7 sources, of which 2 fall inside the half-mass radius, and long-term (28 months) variability for 10 further sources, of which 2 fall inside the half-mass radius. Ultraviolet counterparts are found for 8 Chandra sources in the core, of which 2 have good matching probabilities and have ultraviolet properties expected for cataclysmic variables.

We find one likely neutron star-quiescent low-mass X-ray binary and 8 cataclysmic variable candidates in the core of NGC 2808 . The other sources are cataclysmic variable candidates, but some could possibly be active binaries or millisecond pulsars. We find a possible deficit of X-ray sources compared to 47 Tuc which could be related to the metallicity content and the complexity of the evolution of NGC 2808 .

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More information

Published date: 1 November 2008
Keywords: globular clusters, individual, NGC 2808, x-rays, general binaries, close novae, cataclysmic variables

Identifiers

Local EPrints ID: 144193
URI: http://eprints.soton.ac.uk/id/eprint/144193
ISSN: 0004-6361
PURE UUID: d780660e-996f-4986-8ed0-e19947078f78

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Date deposited: 16 Apr 2010 15:06
Last modified: 04 Mar 2019 17:31

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