  The 11th magnitude star LS IV -08 3 has been classified previously as an OB
star in the Luminous Stars survey, or alternatively as a hot subdwarf. It is
actually a binary star. We present spectroscopy, spectroscopic orbital
elements, and time series photometry, from observations made at the Kitt Peak
National Observatory 2.1m, Steward Observatory 2.3m, MDM Observatory 1.3m and
2.4m, Hobby-Eberly 9.2m, and Michigan State University 0.6m telescopes. The
star exhibits emission of varying strength in the cores of H and He I
absorption lines. Emission is also present at 4686 Angstroms (He II) and near
4640/4650 Angstroms (N III/C III). Time-series spectroscopy collected from 2005
July to 2007 June shows coherent, periodic radial velocity variations of the
H-alpha line, which we interpret as orbital motion with a period of
0.1952894(10) days. High-resolution spectra show that there are two emission
components, one broad and one narrow, moving in antiphase, as might arise from
an accretion disk and the irradiated face of the mass donor star. Less
coherent, low-amplitude photometric variability is also present on a timescale
similar to the orbital period. Diffuse interstellar bands indicate considerable
reddening, which however is consistent with a distance of ~100-200 pc. The star
is the likely counterpart of a weak ROSAT X-ray source, whose properties are
consistent with accretion in a cataclysmic variable (CV) binary system. We
classify LS IV -08 3 as a new member of the UX UMa subclass of CV stars.
