Mapping the accretion disc of the short period eclipsing binary SDSS J0926+3624

TL;DR

This study analyzes optical photometry of the eclipsing binary SDSS J0926+3624, revealing an increasing orbital period, a faint accretion disc, and a lower-than-expected mass transfer rate, providing insights into its accretion dynamics.

Contribution

The paper provides the first detailed eclipse mapping and period analysis of SDSS J0926+3624 during quiescence, highlighting gas stream overflow and revised accretion rate estimates.

Findings

Orbital period is increasing at a rate of (3.2 ± 0.4)×10^{-13} s/s.

No evidence of orbital hump or superhumps in light curves.

Accretion disc mass transfer rate is significantly lower than conservative evolution models.

Abstract

We report the analysis of time-series of optical photometry of SDSS J0926+3624 collected with the Liverpool Robotic Telescope between 2012 February and March while the object was in quiescence. We combined our median eclipse timing with those in the literature to revise the ephemeris and confirm that the binary period is increasing at a rate $\dot{P}=(3.2 \pm 0.4)\times 10^{-13} \, s/s$. The light curves show no evidence of either the orbital hump produced by a bright spot at disc rim or of superhumps; the average out-of-eclipse brightness level is consistently lower than previously reported. The eclipse map from the average light curve shows a hot white dwarf surrounded by a faint, cool accretion disc plus enhanced emission along the gas stream trajectory beyond the impact point at the outer disc rim, suggesting the occurrence of gas stream overflow/penetration at that epoch. We estimate a disc mass input rate of $\dot{M}=(9 \pm 1)\times 10^{-12}\,M_\odot \,yr^{-1}$, more than an order of magnitude lower than that expected from binary evolution with conservative mass transfer.