Photometric Analysis of the OGLE Heartbeat Stars
  We present an analysis of 991 heartbeat stars (HBSs) from the OGLE Collection
of Variable Stars (OCVS). The sample consists of 512 objects located toward the
Galactic bulge (GB), 439 in the Large Magellanic Cloud (LMC) and 40 in the
Small Magellanic Cloud (SMC). We model the $I$-band OGLE light curves using an
analytical model of flux variations, reflecting tidal deformations between
stars. We present distributions of the model parameters that include the
eccentricity, orbital inclination, and argument of the periastron, but also the
period-amplitude diagrams. On the Hertzsprung-Russell (HR) diagram, our HBS
sample forms two separate groups of different evolutionary status. The first
group of about 90 systems, with short orbital periods ($P\lesssim50$~days),
consists of an early-type primary star lying on (or close to) the main sequence
(MS). The second group of about 900 systems, with long orbital periods
($P\gtrsim100$~days), contains a red giant (RG). The position of RG HBSs on the
period-luminosity diagram strongly indicates their binary nature. They appear
to be a natural extension of confirmed binary systems that include the OGLE
ellipsoidal and Long Secondary Period (LSP) variables. We also present a
time-series analysis leading to detection of tidally-excited oscillations
(TEOs). We identify such pulsations in about 5\% of stars in the sample with a
total number of 78 different modes. This first relatively large homogeneous
sample of TEOs allowed us to construct a diagram revealing the correlation
between the TEO's orbital harmonic number and the eccentricity of the host
binary system.
