Spectroscopy of TT Arietis in "positive superhumps" state^*

Institute of Astronomy, Bulgarian Academy of Sciences, 72 Tsarigradsko Shouse Blvd., 1784 Sofia, Bulgaria

Corresponding author: V. Stanishev, vall@astro.bas.bg

Received: 11 April 2001
Accepted: 8 August 2001

Abstract

An analysis of spectral and photometric observations of the novalike TT Ari obtained in the interval 1999-2001 is presented. The photometry in November 1999 shows "positive superhumps" with a period of 014815 and full amplitude 0.13-0.14 mag. The emission lines equivalent widths are also modulated with the "positive superhumps" period, as its value in the interval from August 2000 to January 2001 is 0148815. The analysis shows that the flux in the emission lines vary in anti-phase with the continuum. It is found that Hα asymmetry is modulated with the expected precessional period of 181715 supporting the precession accretion disc model for the "positive superhumps" observed in TT Ari. An expansion of the TT Ari accretion disc due to a mass transfer rate reduction is proposed as a possible mechanism for the appearance of the "positive superhumps". The Hα profile shows a weak, blue-shifted absorption, whose strength is modulated with the orbital period of the system. The Hα Doppler tomogram reveals the presence of an asymmetric source of emission in the accretion disc. Eclipse of this emission source by the outflowing wind is the most likely explanation of the phase dependent Hα P-cygni profile. The Hei λ6678 tomogram shows a strong asymmetric emission source located at the back side of the disc. The asymmetric emission sources in Hα and Hei λ6678 tomograms are thus located on the opposite sides of the system mass center. The emission of the secondary is detected in Hei λ6678 Doppler tomogram, which allows us to secure the absolute phasing of the radial velocities. We derive a new orbital ephemeris of TT Ari by analysis of all availible high state radial velocities.