An IUE spectroscopic study of the ultra-short-period dwarf nova T Leonis in outburst

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 STI 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., accretion rates 10(-11)-10(-7) M. yr(-1), and disk inclination angles of 40 degrees and 80 degrees. 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., i similar or equal to 40 degrees, M similar or equal to 10(-9) M. 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.