BV Photometry of the Ultracompact Binary Star GP Com

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 ≈ 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 ±3000 K. We estimate mass accretion rate onto the white dwarf  of about $$2\times 10^{-12}  \ {\rm M}_\odot\ {\rm yr}^{-1}$$, consistent with the predicted rate for a cool donor.

The data are available on Zenodo:  zenodo.org/records/18768211.