D. Boneva | Searcharxiv

arXiv2026

BV photometry of the ultracompact binary star GP Com

We present optical B and V band photometry of GP Com - an ultracompact binary consisting of an accreting white dwarf and helium secondary component. Our data set contains 7.7 hours observations in V band with the 2.0m telescope and 2.9 hours simultaneous observations in B and V bands with the 1.5m telescope of the Rozhen National Astronomical Obsevatory, Bulgaria. The observations cover of about 13 orbital periods. We find an orbital modulation with amplitude 0.04-0.05 mag in B and V bands. Adopting that it is due to a bright spot, we estimate its temperature 19700 \pm 3000 K. We estimate mass accretion rate onto the white dwarf of about 2.10^{-12} M_sun/yr, consistent with the predicted rate for a cool donor. The data are available on Zenodo: zenodo.org/records/18768211.

astro-ph.SR↗

arXiv2018

The recurrent nova RS Oph - simultaneous B and V band observations of the flickering variability

We performed 48.6 hours (in 28 nights) of simultaneous B and V band observations of the flickering variability of the recurrent nova RS Oph in quiescence. During the time of our observations the brightness of the system varied between 13.2 > B > 11.1 and the colour in the range 0.86 < B-V < 1.33 . We find that RS~Oph becomes more blue, as it becomes brighter, however the hot component becomes more red as it becomes brighter (assuming that the red giant is non-variable). During all the runs RS Oph exhibits flickering with amplitude 0.16 - 0.59 mag in B band. For the flickering source we find that it has colour -0.14 < B-V < 0.40, temperature in the range 7200 < T_fl < 18900, and average radius 1.1 < R_fl < 6.7 R_sun. We do not find a correlation between the temperature of the flickering and the brightness. However, we do find a strong correlation (correlation coefficient 0.81, significance 1.1x10^{-7} ) between B band magnitude and the average radius of the flickering source - as the brightness of the system increases the size of the flickering source also increases. The estimated temperature is similar to that of the bright spot of cataclysmic variables. The persistent presence of flickering indicates that the white dwarf is actively accreting material for the next outburst.

astro-ph.SR↗