Search for dormant black holes in ellipsoidal variables I. Revisiting the expected amplitudes of the photometric modulation
Abstract
Ellipsoidal variables present lightcurve modulations caused by stellar distortion, induced by tidal interaction with their companions. An analytical approximated model of the ellipsoidal modulation is given as a discrete Fourier series by Morris & Naftilan. Based on numerical simulations using the PHOEBE code, we present here updated amplitudes of the first three harmonics of the model. The expected amplitudes are given as a function of the mass ratio and inclination of the binary system and the fillout factor of the primary  the ratio between the stellar radius and that of its Roche lobe. The corrections can get up to 30 per cent relative to the Morris & Naftilan model for fillout factors close to unity. The updated model can be instrumental in searching for shortperiod binaries with compactobject secondaries in large data sets of photometric light curves. As shown in one OGLE lightcurve example, the minimum mass ratio can be obtained by using only the amplitudes of the three harmonics and an estimation of the stellar temperature. High enough amplitudes can help to identify binaries with mass ratios larger than unity, some of which might have compact companions.
 Publication:

Monthly Notices of the Royal Astronomical Society
 Pub Date:
 February 2021
 DOI:
 10.1093/mnras/staa3305
 arXiv:
 arXiv:2008.11209
 Bibcode:
 2021MNRAS.501.2822G
 Keywords:

 methods: data analysis;
 techniques: photometric;
 binaries: close;
 stars: black holes;
 Xrays: binaries;
 Astrophysics  Solar and Stellar Astrophysics
 EPrint:
 13 pages, 6 figures