Phase-resolved spectroscopy of the helium dwarf nova `SN 2003aw' in quiescence

Abstract

High time resolution spectroscopic observations of the ultracompact helium dwarf nova `SN2003aw' in its quiescent state at V~ 20.5 reveal its orbital period at 2027.8 +/- 0.5 s or 33.80 min. Together with the photometric `superhump' period of 2041.5 +/- 0.5 s, this implies a mass ratio q~ 0.036. We compare both the average and time-resolved spectra of `SN2003aw' and Sloan Digital Sky Survey (SDSS) J124058.03-015919.2. Both show a DB white dwarf spectrum plus an optically thin, helium-dominated accretion disc. `SN2003aw' distinguishes itself from the SDSS source by its strong calcium H & K emission lines, suggesting higher abundances of heavy metals than the SDSS source. The silicon and iron emission lines observed in the SDSS source are about twice as strong in `SN2003aw'. The peculiar `double bright spot' accretion disc feature seen in the SDSS source is also present in time-resolved spectra of `SN2003aw', albeit much weaker.