The T Tauri star RX J1608.6-3922 -not an eclipsing binary but a spotted single star^*

¹ Max-Planck-Institut für Extraterrestrische Physik, Giessenbachstrasse 1, 85748 Garching, Germany
² Thüringer Landessternwarte Tautenburg, Karl-Schwarzschild-Observatorium, Sternwarte 5, 07778 Tautenburg, Germany
³ Instituto de Astrofísica de Andalucía (CSIC), Apdo. 3004, 18080 Granada, Spain
⁴ Homi Bhabha Centre for Science Education (Tata Inst. of Fundamental Research), V. N. Purav Marg Mankhurd, Mumbai 400088, India

Corresponding author: V. Joergens, viki@mpe.mpg.de

Received: 13 March 2001
Accepted: 10 May 2001

Abstract

High-resolution spectroscopy and photometric monitoring of the pre-main sequence star RX J1608.6-3922 shows that it is not an eclipsing binary, as previously claimed. Radial velocity measurements covering suitable time spans in order to detect a spectroscopic binary with the claimed period of about 7 days have been performed. The scatter of the radial velocity does not exceed 2.4 km s^-1, defining an upper mass limit of 24 for any eclipsing companion orbiting this star with the claimed period. Photometric observations of RX J1608.6-3922 in 7 consecutive nights (i.e. as long as the claimed orbital period) reveal brightness variations of the order of 0.2 mag with a period of 3.6 days. The shape of the detected light curve differs from a light curve of the star recorded in 1996. The small variations of the radial velocity, the variable shape of the light curve, as well as () color variations suggest that the flux of RX J1608.6-3922 is modulated by spots on the stellar surface with a rotational period of 3.6 days. The stellar activity of this star seems to be highly variable, taking into account the variable shape of the light curve, with an amplitude varying from 0.5 to 0.2 mag in a few years, as well as hints for a variable H_α equivalent width.