V485 Centauri: A dwarf nova with a 59(m) orbital period

We present time resolved photometry and spectroscopy of the dwarf nova V485 Cen. Significant radial velocity variations are detected in Ha only for a period equal to the previously detected 59 min photometric period (Augusteijn et al. 1993), and we conclude that this is the orbital period of the system. Ha shows two components which vary with this period. One component dominates the line wings and originates from a region centered on the white dwarf. The second component dominates the line center and originates in the hot spot (the so-called S-wave). Using various observational constraints we derive a mass ratio of q = M(WD)/M(sec) similar to 2.6 and a inclination of i similar to 20-30 degrees. Strong evidence is found for a significant contribution from the secondary to the spectrum at wavelengths longer than similar to 5900 Angstrom. We discuss the discovery of a 59(m) orbital period in the framework of evolutionary ideas about cataclysmic variables. The most likely explanation is that the secondary has a low, but finite, hydrogen content.