The short period multiplicity among T Tauri stars

We present the results of high-resolution spectroscopic observations carried out over three years aimed at estimating the shortperiod ( P orb<100 days) binary frequency of a sample of T Tauri stars in Oph-Sco, Cha, Lup, CrA star forming regions (SFRs), already observed with high angular resolution techniques by Ghez et al. (1993) and by Ghez et al. (1997) to detect wider components. When combining all four SFRs, the short-period binary frequency is indistinguishable from that found by Duquennoy & Mayor (1991) for the solar-type field stars which is also consistent with the previous result obtained by Mathieu (1992, 1994). When Oph-Sco is analyzed separately, it seems that there is an excess of short-period binaries of a factor 2-2.5. On the contrary, short-period binary systems seem to be absent in the sample containing stars in Cha/Lup/CrA. Such a trend was equally found by Mathieu (1992) in Taurus. An excess of spectroscopic systems among the components of visual multiple systems is also observed.