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

High-resolution spectroscopy and photometric monitoring of the pre-main seq uence star RX J1608.6-3922 shows that it is not an eclipsing binary, as pre viously 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 exc eed 2.4 km s(-1), defining an upper mass limit of 24 M-Jupiter for any ecli psing companion orbiting this star with the claimed period. Photometric obs ervations of RX J1608.6-3922 in 7 consecutive nights (i.e. as long as the c laimed 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 f rom 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 (B-V) c olor variations suggest that the flux of RX J1608.6-3922 is modulated by sp ots on the stellar surface with a rotational period of 3.6 days. The stella r activity of this star seems to be highly variable, taking into account th e 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-alpha equivalent width.