EDP Sciences
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Volume 378, Number 3, November II 2001
Page(s) 837 - 842
Section Formation, structure and evolution of stars
DOI http://dx.doi.org/10.1051/0004-6361:20011276

A&A 378, 837-842 (2001)
DOI: 10.1051/0004-6361:20011276

X-ray and optical periodicities in X-ray binaries I. A0535+26

V. Larionov1, 2, V. M. Lyuty3 and G. V. Zaitseva3

1  Astronomical Institute of St. Petersburg University, Petrodvorets, Bibliotechnaya Pl. 2, 198504, Russia
2  Isaac Newton Institute of St. Petersburg, Chile, St. Petersburg Branch, Russia
3  P. K. Shternberg Astronomical Institute, Moscow, Russia

(Received 16 January 2001 / Accepted 26 July 2001)

A homogeneous set of UBV photometry (354 data points obtained between 1983 and 1998) for the Be/X-ray binary A0535+26 = V725 Tau is analysed, aiming to look for possible periodic component(s). After subtraction of the long-term variation it was found that only a $\approx $103d periodic component remains in the power spectra in both the V and B colour bands. The probability of chance occurrence of such a peak is less than 0.1% . There are no signs of optical variability at the X-ray period ($\approx $111d). We discuss possible reasons for a 103-day modulation and suggest that it corresponds to a beat frequency of the orbital period of the neutron star and the precession period ($\approx $1400d) either of an accretion disc around the neutron star or a warped decretion disc around the Be star.

Key words: stars: binaries: general -- stars: circumstellar matter -- stars: individual: V725 Tau -- stars: pulsars: individual: A0535+26 -- stars: variables: general -- accretion, accretion discs

Offprint request: V. Larionov, VML@VL1104.spb.edu

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