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Spectroscopy of the enigmatic short-period cataclysmic variable IR Com in an extended low state

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We report the occurrence of a deep low state in the eclipsing short-period cataclysmic variable IR Com, lasting more than two years. Spectroscopy obtained in this state shows the system as a detached white dwarf plus low-mass companion, indicating that accretion has practically ceased. The spectral type of the companion is M6-7, suggesting a mass of 0.15-0.20 Msun. Its radial velocity amplitude, K_2=419.6+/-3.4 km/s, together with the inclination of 75deg - 90deg implies 0.91Msun<Mwd<1.05Msun. We estimate the white dwarf temperature to be ~15000K, and the absence of Zeeman splitting in the Balmer lines rules out magnetic fields in excess of ~5MG. While all the binary and stellar parameters are typical for a CV near the lower edge of the orbital period gap, the long-term behaviour of IR Com defies its classification, in particular the occurrence of a deep, long low state is so far unique among short-period CVs that are not strongly magnetic.

Authors:  C.J. Manser, B.T. Gaensicke

Read the paper on arXiv

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