White Dwarf Photospheric Abundances in Cataclysmic Variables—II. White Dwarfs with and without a Mask

Abstract

Abstract Taking advantage of the now-available Gaia EDR3 parallaxes, we carry out an archival Hubble Space Telescope (HST) far-ultraviolet spectroscopic analysis of 10 cataclysmic variable systems, including five carefully selected eclipsing systems. We obtain accurate white dwarf (WD) masses and temperatures, in excellent agreement with the masses for four of the eclipsing systems. For three systems in our sample, BD Pav, HS 2214, and TT Crt, we report the first robust masses for their WDs. We modeled the absorption lines to derive the WD chemical abundances and rotational velocities for each of the 10 systems. As expected, for five higher-inclination (i ≳ 75°) systems, the model fits are improved with the inclusion of a cold absorbing slab (a curtain masking the WD) with N H ≈ 1020–1022 cm−2. Modeling of the metal lines in the HST spectra reveals that seven of the 10 systems have significant subsolar carbon abundance, and six have subsolar silicon abundance, thereby providing further evidence that CV WDs exhibit subsolar abundances of carbon and silicon. We suggest that strong aluminum absorption lines (and iron absorption features) in the spectra of some CV WDs (such as IR Com) may be due to the presence of a thin iron curtain (N H ≈ 1019 cm−2) rather than to suprasolar aluminum and iron abundances in the WD photosphere. The derived WD (projected) rotational velocities all fall in the range ≈100–400 km s−1, all sub-Keplerian similar to the values obtained in earlier studies.