K-Band Spectroscopy of (Pre-)Cataclysmic Variables: Are Some Donor Stars Really Carbon Poor?

Abstract

We present a new sample of $K$-band spectral observations for CVs: non-magnetic and magnetic as well as present day and pre CVs. The purpose of this diverse sample is to address the recent claim that the secondary stars in dwarf novae are carbon deficient, having become so through a far more evolved evolution than the current paradigm predicts. Our new observations, along with previous literature results, span a wide range of orbital period and CV type. In general, dwarf novae in which the secondary star is seen show weak to no CO absorption while polar and pre-CV donor stars appear to have normal CO absorption for their spectral type. However, this is not universal. The presence of normal looking CO absorption in the dwarf nova SS Aur and the hibernating CV QS Vir and a complete lack of CO absorption in the long period polar V1309 Ori cloud the issue. A summary of the literature pointing to non-solar abundances including enhanced NV/CIV ratios is presented. It appears that some CVs have non-solar abundance material accreting onto the white dwarf suggesting an evolved secondary star while for others CO emission in the accretion disk may play a role. However, the exact mechanism or combination of factors causing the CO absorption anomaly in CVs is not yet clear.

Accepted in AJ

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• Nova-produced Common Envelope: Source of the Non-solar Abundances and an Additional Frictional Angular Momentum Loss in Cataclysmic Variables
• Life after eruption - III. Orbital periods of the old novae V365 Car, AR Cir, V972 Oph, HS Pup, V909 Sgr, V373 Sct and CN Vel
• Abundance Derivations for the Secondary Stars in Cataclysmic Variables from Near-Infrared Spectroscopy
• X-ray Point Source Populations Constituting the Galactic Ridge X-ray Emission
• A 9-Hr CV With One Outburst in 4 Years of Kepler Data
• White Dwarf Photospheric Abundances in Cataclysmic Variables: I. SS Aurigae and TU Mensae
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• Infrared identification of 2XMM J191043.4+091629.4
• Near-Infrared Spectroscopy of Faint Discrete X-ray Point Sources Constituting the Galactic Ridge X-ray Emission