BLG723.31.34651 as an eclipsing Roche lobe-filling sdOB+WD binary

Abstract

We present a detailed observational analysis of BLG723.31.34651, the fourth reported eclipsing member of the class of Roche lobe-filling hot subdwarfs, using time series spectroscopy and multi-band photometric observations from the Goodman High Throughput Spectrograph on the 4.1-m SOAR telescope. Our light curves show periodic photometric variability at $P=64~{\rm min}$ from the tidally-deformed hot subdwarf donor and deep eclipses of the donor by an opaque accretion disc. We report two light curve model solutions that agree with each other to within $2σ$, both suggesting that BLG723.31.34651 contains a typical hot subdwarf donor, a white dwarf accretor, and an irradiated opaque accretion disc. Our spectroscopic analysis identifies statistically significant phase-dependent variations in the effective temperature and surface gravity coinciding with the phase-dependent variations seen in our observed light curves. We attribute these variations to a combination of intrinsic variations in local atmospheric parameters due to tidal deformation of the donor and unmodeled spectroscopic flux contributions from an accretion disc.