Multifilter Time-series Observations of Eleven Blue Short-period ATLAS Variable Stars

Eleven periodic variable stars were observed photometrically through two to four filters from the set UBVR _C I _C . Phase-folded data for each star cover full cycles of variation. Spectral energy distributions, based on absolute photometry extracted from the literature, are used to inform models of the stars. The stars include four eclipsing systems with hot subdwarfs of spectral type O or B (sdO/B). Periods are in the range 1.8–2.2 hr. Four reflection-effect binaries, with amplitudes as large as 0.5 mag in the R _C filter were observed; periods range from 1.6 to 2.4 hr. In two of these latter systems, the primary stars are also sdB stars, while two have white-dwarf components. In all eight of these binaries the companion stars are probably M dwarfs. The remaining three stars are pulsators: one large-amplitude δ Scuti star previously misclassified as an eclipsing system; one field SX Phe star near the Galactic plane; and one multiperiodic high-luminosity star of unknown type. The amplitude is usually a strong function of the wavelength in pulsating stars, but this is not the case for the high-luminosity variable. One possible explanation is that the luminous star has a pulsating companion. The SX Phe and high-luminosity star are both heavily reddened ( A _V > 5 mag).