New photometry of 12 ultrashort-period late-type binary stars

Abstract

Candidate late-type binary stars were selected on the basis of their red g - i and r - z colours, and short (0.1159-0.2059 d) published periods. At least one cycle of variation of each star was observed in the R_C and I_C bands. For the five brightest stars, observations were also obtained in V. Typically ~17 standardized photometric measurements of each of the stars, ranging over the optical and infrared, are available from various surveys. These were used to accurately determine the reddenings and effective temperatures. In all but one case Gaia parallaxes are available, so that the luminosities of the binaries could also be estimated. Deduced spectral types are in the range M2-M4.5. Preliminary modelling suggests that half the stars may be in contact configurations.