SPECTROSCOPY OF THE WHITE-DWARF RED DWARF BINARY RE J1629+780

Low-resolution spectra of the close white dwarf-red dwarf binary RE J1 629 + 780 are presented, The spectra, taken over the range 3400-8900 A ngstrom, show Balmer absorption features from the white dwarf and TiO bands and NaI absorption lines from the red dwarf, Also present in the spectra are narrow Balmer and CaII K lines in emission, believed to o riginate from the secondary star, probably as a result of reprocessed light from the hot white dwarf and/or the presence of active regions. From the TiO band ratio we estimate the spectral type of the red dwarf as Boeshaar dM4. Using pure hydrogen model fits to the H beta, H gamm a, H delta and H epsilon Balmer absorption features, we derive a tempe rature of 41800+/-2000 K and a surface gravity of log g = 8.0+/-0.5 fo r the DA white dwarf, from which we obtain a mass of M(1) = 0.65 +/- 0 .25 M.. We discuss the implications of our results and carry out a pre liminary evolutionary analysis.