Ellipsoidal Variables in the SWEEPS Field

We monitored the SWEEPS field in the Galactic bulge using the Hubble Space Telescope (HST) over a 7-day interval in February 2004, employing the V (F606W) and I (F814W) filters. By combining all exposures, we obtained extremely deep V and I images, detecting approximately 245,000 stars down to a limiting magnitude of V ~ 30. To identify ellipsoidal variables in the field, we searched all the observed light curves for significant peaks in their power spectra, using a threshold that excludes false positives. After masking out red giants—most of which show variability at the milli-magnitude level—we identified a total of 1145 variable stars with significant Fourier peaks. This sample likely includes W UMa, δ Scuti, BY Draconis, RR Lyrae, and other types of variables. Among them, 169 are eclipsing binaries. All eclipsing systems exhibiting sinusoidal variations have amplitudes that suggest companion masses exceeding the planetary mass range.