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 short-period (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.