A PHOTOMETRIC AND SPECTROSCOPIC STUDY OF THE CATACLYSMIC VARIABLE SX-LEONIS-MINORIS IN QUIESCENCE AND SUPEROUTBURST

We present CCD imaging, CCD photometry on long and short timescales, a nd time-resolved spectroscopy of SX LMi, a new SU Ursae Majoris type d warf nova. The quiescent optical spectrum shows broad double-peaked Ba lmer, He I, and He II emission lines, similar to other quiescent dwarf novae. Absorption lines from a late-type secondary are not detected. Time-resolved spectra obtained in quiescence reveal radial velocity va riations of the Palmer emission lines on a period of 0.06717 +/- 0.000 11 days, or 96.72 +/- 0.16 minutes, with only a slight possibility of a daily cycle-count error. Optical photometry obtained between 1987 an d 1991 shows flickering with a peak-to-peak amplitude of similar or eq ual to 0.18 mag. The binary orbital period can sometimes be seen in th e photometric record. Long-term photometric monitoring by Indiana Univ ersity's robotic telescope RoboScope for a 3 year period between 1992 October and 1995 June shows seven well-defined outbursts and marginall y detects a few others. The outburst interval varies between 34 and 64 days. During the 1994 December outburst, optical photometric observat ions show that SX LMi exhibited superhumps with a period of 0.06893 +/ - 0.00012 days, which is 2.6% +/- 0.2% longer than the orbital period, as expected for a normal SU UMa star at this period. Spectra obtained during superoutburst show dramatic variations in the emission-line pr ofiles on timescales of 10 minutes. Profile fits indicate that underly ing absorption contributes to the shape of the Balmer emission-line pr ofiles during superoutburst as in other dwarf novae in outburst or sup eroutburst. Direct images in good seeing show a similar to 19 mag comp anion star 1 ''.95 from SX LMi.