BV photometry of the ultracompact binary star GP Com

TL;DR

This study presents optical photometry of the ultracompact binary GP Com, revealing orbital modulation, estimating the bright spot temperature, and measuring the mass accretion rate, with data publicly available online.

Contribution

First detailed optical photometry of GP Com covering multiple orbital periods, estimating bright spot temperature and accretion rate.

Findings

Detected orbital modulation with 0.04-0.05 mag amplitude.

Estimated bright spot temperature at 19700 ± 3000 K.

Measured mass accretion rate of about 2×10^{-12} M_sun/yr.

Abstract

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.