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Astron. Astrophys. 325, 1035-1038 (1997)

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Optical photometry of Sco X-2 *

O. Barziv 1, E. Kuulkers 2, M. Méndez 3, 4, F. van der Hooft 3, P.J. Groot 3, M. van der Klis 3, C. Kemper 5 and J. van Paradijs 3, 6

1 European Southern Observatory, Karl-Schwarzschild-Strasse 2, D-85748 München, Germany
2 University of Oxford, Nuclear and Astrophysics Laboratory, Keble Road, Oxford OX1 3RH, UK
3 Astronomical Institute "Anton Pannekoek", University of Amsterdam and Center for High-Energy Astrophysics, Kruislaan 403 1098 SJ Amsterdam, The Netherlands
4 Facultad de Ciencias Astronómicas y Geofisicas, Universidad Nacional de La Plata, Paseo del Bosque S/N, 1900 La Plata, Argentina
5 Leiden Observatory, Postbus 9513, 2300 R.A. Leiden, The Netherlands
6 University of Alabama, Huntsville, AL 35899, USA

Received 22 October 1996 / Accepted 11 April 1997


We present optical photometry of the galactic bulge low-mass X-ray binary GX 349+2 (Sco X-2) obtained in July 1993 and March 1996. Short-term variations up to one magnitude are present on time scales of a few hours, which are related to the known X-ray behaviour of the source.

We find (equally strong) evidence for a periodicity at either 22.3 hours or at 14.9 days. These periodicities are close to the 22 hour reported by Wachter & Margon (1996) and the 14 day period reported by Southwell et al. (1996). The two periods are related to each other through aliasing with the frequency of observations, which is approximately one day. We therefore suggest that one of the periods reported is the true (orbital) period, whereas the other is the [FORMULA] 1 day alias. This confirms that both reported periods are present in the data. Independent of which is the real one, we conclude that the orbital period if Sco X-2 is relatively long.

Key words: stars: binaries: eclipsing – stars: imaging – stars: individual

* Based on observations made at the European Southern Observatory.

Send offprint requests to: O. Barziv (obarziv@eso.org)

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© European Southern Observatory (ESO) 1997

Online publication: April 28, 1998