Long-term color variations of the peculiar X-ray binary V Sagittae^*

¹ Astronomical Institute, Academy of Sciences, 251 65 Ondřejov, Czech Republic
² Sternberg Astronomical Institute, Moscow State University, Universitetsky Prospect 13, 119899 Moscow, Russia
³ Department of Astronomy, Odessa State University, T.G. Shevchenko park, Odessa, 65014, Ukraine

Corresponding author: V. Šimon, simon@asu.cas.cz

Received: 29 February 2000
Accepted: 26 October 2000

Abstract

We present an analysis of the color variations of the X-ray binary V Sge during high, medium and low state of its activity over the years 1995-1997, using UBV data. We resolved the track of V Sge in the color diagrams ( and versus mag(V)) during transitions between the states and show that the color variations on the orbital time scale are significantly smaller than the changes caused by the long-term activity. The mean decreases by 0.15 mag during the upper part of the transition (brightness higher than 11.5 mag(V)) from the low to the high state but stays almost constant below this level. On the contrary, does not change significantly during the whole transition. Comparison of our data with those of Herbig et al. ([CITE]) shows that although the character of the long-term activity in V Sge changed significantly during the last decades (Šimon & Mattei [CITE]) the colors and their variations with the brightness level remained similar.