TT Arietis: the low state revisited

Abstract

We present optical and ultraviolet spectroscopy of TT Ari obtained during the 1982-85 low state. In November/December 1983, accretion had almost completely ceased, unveiling both the white dwarf and the secondary star. The IUE spectrum obtained during that occasion contains absorption lines of Lyalpha , \Si IV, \C IV, and \He II. We derive a photospheric temperature of T_wd=39 000 K and find the abundances of Carbon and Helium to be 0.5 and 2.0 times solar, respectively. An upper limit of vsin ila750 km s(-1) is derived from the metal line profiles. Comparison with the IUE spectrum taken one year earlier during the low state shows no evidence for cooling of the white dwarf over a time span of one year. The optical spectrum displays Balmer absorption lines from the white dwarf, overlayed with narrow emission lines, as well as the TiO absorption bands of the secondary star, for which we derive a spectral type M3.5+/-0.5. A distance of d=335+/-50 pc is derived from both, the white dwarf and the secondary star. The data indicate that the low-state accretion disc in TT Ari was optically thin at least for rla12 R_wd. Based on observations made with the International Ultraviolet Explorer, retrieved from the IUE FA and on observations at the European Southern Observatory La Silla (Chile) with the 1.5-m