Spectral and photometric observations of TT Ari. III.

Abstract

The nova-like cataclysmic variable (CV) TT Ari was detected in its second deep minimum in November 2009. Study of its evolutionary phase is very important for research on the nature of CVs in the VY Scl group. During this phase the spectral energy distribution of the star changed rapidly. The emission lines of elements with high excitation, such as HeII λ4686 and NIII/CIII, as well as broad absorption in the hydrogen Balmer series, originating in the photosphere of the white dwarf or in the lower layers of an accretion disk, vanished. The average ratio of the intensities of the Balmer series emission lines in the normal state and in the deep low state can be explained in terms of a simple photoionization-recombination model. At the same time, the intensity ratios of the triplet-singlet levels of neutral helium, HeIλ5876/ HeIλ6678, differ greatly in the normal state of the star and in its deep minimum. In the deep minimum, the star’s spectrum contains only a very faint trace of the G band at a wavelength λ4300A, together with flarelike events with amplitudes up to Δm ≈ 2 m .0 or greater. These and some other observed characteristics indicate that during the deep minimum it is mainly emission from the secondary companion of the binary system, which is probably a T Tau star of an early K spectral class, that is observed.