A Photometric and Spectroscopic Study of the Cataclysmic Variable SX Leonis Minoris in Quiescence and Superoutburst

Abstract

We present CCD imaging, CCD photometry on long and short timescales, and time-resolved spectroscopy of SX LMi, a new SU Ursae Majoris type dwarf nova. The quiescent optical spectrum shows broad double-peaked Balmer, 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 variations of the Balmer emission lines on a period of 0.06717 ^0.00011 days, or 96.72 ^0.16 minutes, with only a slight possibility of a daily cycle-count error. Optical photometry obtained between 1987 and 1991 shows ickering with a peak-to-peak amplitude of ^0.18 mag. The binary orbital period can sometimes be seen in the photometric record. Long-term photometric monitoring by Indiana Universitys robotic telescope RoboScope for a 3 year period between 1992 October and 1995 June shows seven well-dened outbursts and marginally detects a few others. The outburst interval varies between 34 and 64 days. During the 1994 December outburst, optical photometric observations 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 proles on timescales of 10 minutes. Prole ts indicate that underlying absorption contributes to the shape of the Balmer emission-line proles during superoutburst as in other dwarf novae in outburst or superoutburst. Direct images in good seeing show a D19 mag companion star from SX LMi. 1A .95