PHYSICAL-PROPERTIES OF 90 AU TO 250 AU PRE-MAIN-SEQUENCE BINARIES

We have analyzed photometric and spectroscopic data of a sample of 14 spatially resolved pre-main-sequence binaries (separations 0./6 '' to 1.7 '') in the nearby (150 pc) low-mass star-forming rgions of Chamael eon, Lupus, and rho Ophiuchi. The spectroscopic data have been obtaine d with the ESO New Technology Telescope (NTT) at La Silla under subarc sec seeing conditions. All binaries (originally unresolved) were ident ified as pre-main-sequence stars based on their strong H alpha emissio n - which classifies them as classical T Tauri stars - and their assoc iation with dark clouds. One of the presumed binaries turned out to be a likely chance projection with the ''primary'' showing neither H alp ha emission nor Li absorption. Using the spectral A index (as defined by Kirkpatrick et al. 1991), which measures the strength of the CaH ba nd at 697.5 nm relative to the nearby continuum, as a luminosity class indicator, we could show that the classical T Tauri stars in our samp le tend to be close to luminosity class V. Eight out of the 14 pairs c ould be placed on an H-R diagram. A comparison with theoretical pre-ma in-sequence evolutionary tracks yields that for all pairs the individu al components appear to be coeval within the observational errors. Thi s finding is similar to Hartigan et al. (1994) who detected that two t hird of the wider pairs with separations from 400 AU to 6000 AU are co eval. However, unlike Hartigan et al. for the wider pairs, we find no non-coeval pairs among our sample. Thus, the formation mechanism for a significant fraction of the wider pre-main-sequence binaries might be different from that of closer pre-main-sequence binaries. All of the latter appear to have formed simultaneously.