MACHO 311.37557.169: A VY Scl star

Abstract

Optical surveys, such as the MACHO project, often uncover variable stars whose classification requires follow-up observations by other instruments. We performed X-ray spectroscopy and photometry of the unusual variable star MACHO 311.37557.169 with XMM-Newton in April 2018, supplemented by archival X-ray and optical spectrographic data. The star has a bolometric X-ray luminosity of about 1 × 10 32 erg s −1 cm −2 and a heavily absorbed two-temperature plasma spectrum. The shape of its light curve, its overall brightness, its X-ray spectrum, and the emission lines in its optical spectrum suggest that it is most likely a VY Scl cataclysmic variable.