Astron. Astrophys. 327, 137-144 (1997)

Astrometry of the globular cluster 47 Tucanae
and possible optical identification of X-ray sources

M. Geffert ¹, M. Aurière ² and L. Koch-Miramond <sup>3

1</sup> Sternwarte der Universität Bonn, Auf dem Hügel 71, D-53121 Bonn, Germany
² Observatoire du Pic du Midi, UMR 5572, CNRS, F-65200 Bagnères de Bigorre, France
³ Service d'Astrophysique Centre d'Etudes de Saclay, F-91191 Gif-sur-Yvette Cedex, France

Received 6 August 1996 / Accepted 11 July 1997

Abstract

Positions of stars of 47 Tuc have been derived by the use of photographic plates and CCD frames (ESO La Silla) and data from the Hubble Space Telescope (HST). The positions have been determined with respect to the PPM, which is based on the FK5 system. We have compared the positions of variable and blue stars in the core of 47 Tuc with those of the X-ray sources found by Hasinger et al. (1994). Taking into account a possible constant shift of the X-ray positions of up to 10 , there are three different solutions which would give identifications of four of the central X-ray sources with blue stragglers and variable stars. We discuss the nature of the X-ray sources and the different possible identifications. Since it is not possible to give a unique identification based on pure astrometric arguments, our positions may be taken for future identifications based on additional astrophysical arguments or coincident observations in different wavelengths. An identification of the X-ray source No. 3 of Hasinger et al. (1994) in the outer field of 47 Tuc with a galaxy was found.

Key words: astrometry - Galaxy: globular clusters: individual: 47 Tuc - X-rays: stars - blue stragglers

Send offprint requests to: geffert@astro.uni-bonn.de

SIMBAD Objects

Contents

• 1. Introduction
• 2. Observations and reductions
• 3. The X-ray positions in the field of 47 Tuc
• 4. Identification of X-ray sources outside the central region of 47 Tuc
  • 4.1. Identification of source No. 3
  • 4.2. Identification of source No. 12
  • 4.3. Identification of source No. 6
• 5. On the identification of the X-ray sources in the core of 47 Tuc
  • 5.1. Is AKO 9 an optical counterpart of one of the central X-ray sources?
  • 5.2. Variable stars as counterparts of the X-ray sources
• 6. Discussion of the different solutions
• 7. Search for optical counterparts of the millisecond pulsars in 47 Tuc
• 8. Summary
• Acknowledgements
• References

© European Southern Observatory (ESO) 1997

Online publication: April 8, 1998
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