We present spectroscopy and time-series photometry of the newly discovered dwarf nova 1RXS J232953.9+062814 .
Photometry in superoutburst reveals a superhump with a period of 66.06 ( 6 ) minutes .
The low state spectrum shows Balmer and HeI emission on a blue continuum , and in addition shows a rich absorption spectrum of type K4 \pm 2 .
The absorption velocity is modulated sinusoidally at P _ { orb } = 64.176 ( 5 ) min , with semi-amplitude K = 348 ( 4 ) km s ^ { -1 } .
The low-state light curve is double-humped at this period , and phased as expected for ellipsoidal variations .
The absorption strength does not vary appreciably around the orbit .
The orbital period is shorter than any other cataclysmic variable save for a handful of helium-star systems and V485 Centauri ( 59 minutes ) .
The secondary is much hotter than main sequence stars of similar mass , but is well-matched by helium-enriched models , indicating that the secondary evolved from a more massive progenitor .
A preliminary calculation in which a 1.2 M _ { \odot } star begins mass transfer near the end of H burning matches this system ’ s characteristics remarkably well .