An IUE Spectroscopic Study of the Ultra-Short-Period Dwarf Nova T Leonis in Outburst

Abstract

The IUE archive contains numerous low-resolution spectra of dwarf novae in outburst but relatively little synthetic spectral analyses of them using realistic accretion disk models with spectral lines. We have examined a series of previously unstudied archival IUE low-resolution short-wavelength prime spectra of the SU UMa-type ultra-short-period dwarf nova T Leonis, obtained continuously through a single dwarf nova outburst. We describe its outburst spectra, characterizing its metallic absorption-line spectrum and the shape of its energy distribution. We estimate a terminal wind velocity of 2500 km s^-1 and report possible evidence of wind variability on timescales of roughly 2 hr, although orbital phase variations cannot be ruled out. We have constructed a grid of optically thick accretion disk models for white dwarf masses 0.6 and 1.0 M_solar, accretion rates 10^-11-10^-7 M_solar yr^-1, and disk inclination angles of 40 deg and 80 deg. We carry out preliminary synthetic accretion disk spectral fitting of T Leo and present the results. Our best-fitting model to a co-addition of three spectra with similar S/N yields M_WD=0.6 M_solar, i~=40 deg, M ~=10^-9 M_solar yr^-1 with an inner disk temperature of 30,000 K and an outer disk temperature of 14,000 K. These results compare favorably with analyses of optical spectra of T Leo in outburst, suggesting that a similar application to other far-UV spectra of dwarf novae in outburst, with a finer grid of disk models, should prove profitable.