CSS1603+19: a low-mass polar near the cataclysmic variable period minimum by Yiqi Liu et al. on Tuesday 29 November

CSS1603+19 is a cataclysmic variable (CV) with an orbital period of 81.96

min, near the minimal period of cataclysmic variables. It is unusual in having

a strong mid-infrared excess inconsistent with thermal emission from a brown

dwarf companion. Here we present time-resolved multi-wavelength observations of

this system. WISE photometry indicates that the mid-infrared excess displays a

one-magnitude eclipsing-like variability during the orbit. We obtained

near-infrared and optical spectroscopy using Gemini, MDM and APO telescopes.

Near-infrared spectra show possible cyclotron features indicating that the

white dwarf has a magnetic field of about 5MG. Optical and near-infrared

spectra display double-peaked emission lines, with both components showing

strong radial velocity variations during the orbital period and with the broad

component leading the narrow component stably by about 0.2 of the orbital

phase. We construct a physical model informed by existing observations of the

system and determine that one component likely originates from the accretion

column onto the magnetized white dwarf in synchronous rotation with the orbital

motion and the other from the Roche overflow point. This allows us to constrain

the masses of the binary components to be $M_1>0.24 M_{\odot}$ for the white

dwarf accretor and $M_2=0.0644\pm0.0074 M_\odot$ for the donor. We classify the

system as an AM Herculis star, or a polar. It has likely completed its stint on

the period gap, but has not yet gone through the period bounce.

arXiv: http://arxiv.org/abs/http://arxiv.org/abs/2211.14945v1