X-ray and optical periodicities in X-ray binaries I. A0535+26
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
Corresponding author: V. Larionov, VML@VL1104.spb.edu
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 
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 (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 (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
© ESO, 2001