The AM canum venaticorum binary SDSS J173047.59+554518.5

Abstract

The AM Canum Venaticorum (AM CVn) binaries are a rare group of hydrogen-deficient, ultrashort period, mass-transferring white dwarf binaries and are possible progenitors of Type Ia supernovae.We present time-resolved spectroscopy of the recently discovered AMCVn binary SDSS J173047.59+554518.5. The average spectrum shows strong double-peaked helium emission lines, as well as a variety of metal lines, including neon; this is the second detection of neon in an AM CVn binary, after the much brighter system GP Com.We detect no calcium in the accretion disc, a puzzling feature that has been noted in many of the longer period AM CVn binaries.We measure an orbital period, from the radial velocities of the emission lines, of 35.2 ± 0.2 min, confirming the ultracompact binary nature of the system. The emission lines seen in SDSS J1730 are very narrow, although double-peaked, implying a low-inclination, faceon accretion disc; using the measured velocities of the line peaks, we estimate i< 11°. This low inclination makes SDSS J1730 an excellent system for the identification of emission lines. © 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.