Astron. Astrophys. 359, 639-645 (2000)

Periodic modulation of the optical counterpart of the X-ray pulsator 1WGA J1958.2+3232. A new intermediate polar ^*

M. Uslenghi ¹, P. Bergamini ¹, S. Catalano ², L. Tommasi ^1,3 and A. Treves <sup>3

1</sup> Istituto di Fisica Cosmica "G.Occhialini", CNR, Via Bassini 15, 20133 Milano, Italy
² Osservatorio Astrofisico di Catania, Via S.Sofia, 78, 95125 Catania, Italy
³ Università degli Studi dell'Insubria, Polo di Como, Dipartimento di Scienze Chimiche, Fisiche e Matematiche, Via Lucini 3, 22100, Como, Italy

Received 13 March 2000 / Accepted 16 May 2000

Abstract

Time-resolved observations of a 6´ x 6´ field, containing the position error boxes of the X-ray source 1WGA J1958.2+3232, were performed in June 1999 with the 91 cm Catania telescope, equipped with a Photon Counting Intensified CCD. The star recently proposed as the optical counterpart of the 1WGA J1958.2+3232, exhibited a strong optical modulation with a period compatible with that seen in X-ray ( 12 min). The optical modulation was detected again in September and October 1999. These results confirm the identification of the optical counterpart and support the classification of 1WGA J1958.2+3232 as a cataclysmic variable, possibly an Intermediate Polar . Modulation at a period twice as large was also found in one observation run, thus suggesting that the true spin period of the White Dwarf could be 24 min rather than 12 min, which would make 1WGA J1958.2+3232 appears to be, among the IPs, the slowest rotator which exhibits double peaked spin profile.

Key words: stars: individual: 1WGA J1958.2+3232 stars: novae, cataclysmic variables stars: binaries: close X-rays: stars instrumentation: photometers

* Based on observations collected at Catania and Asiago Astrophysical Observatories.

Send offprint requests to: M. Uslenghi (uslenghi@ifctr.mi.cnr.it)

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Contents

• 1. Introduction
• 2. Observations
• 3. Data analysis and results
  • 3.1. Source identification and short term variability
  • 3.2. The long term variability
• 4. Discussion
• 5. Conclusions
• Acknowledgements
• References

© European Southern Observatory (ESO) 2000

Online publication: July 7, 2000
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