1997A&A...321..220B -
Astronomy and Astrophysics, volume 321, 220-228 (1997/5-1)
Physical properties of 90AU to 250AU pre-main-sequence binaries.
BRANDNER W. and ZINNECKER H.
Abstract (from CDS):
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 (150pc) low-mass star-forming regions of Chamaeleon, Lupus, and ρ Ophiuchi. The spectroscopic data have been obtained with the ESO New Technology Telescope (NTT) at La Silla under subarcsec seeing conditions. All binaries (originally unresolved) were identified as pre-main-sequence stars based on their strong Hα emission - which classifies them as classical T Tauri stars - and their association with dark clouds. One of the presumed binaries turned out to be a likely chance projection with the "primary" showing neither Hα emission nor Li absorption. Using the spectral A index (as defined by Kirkpatrick et al.
1991ApJS...77..417K), which measures the strength of the CaH band at 697.5nm relative to the nearby continuum, as a luminosity class indicator, we could show that the classical T Tauri stars in our sample tend to be close to luminosity class V. Eight out of the 14 pairs could be placed on an H-R diagram. A comparison with theoretical pre-main-sequence evolutionary tracks yields that for all pairs the individual components appear to be coeval within the observational errors. This finding is similar to Hartigan et al. (
1994ApJ...427..961H) who detected that two third of the wider pairs with separations from 400AU to 6000AU are coeval. 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.
Abstract Copyright:
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Journal keyword(s):
stars: binaries: visual - stars: pre-main-sequence - T association: individual: Chamaeleon, Lupus cloud, rho Oph cloud
Nomenclature:
Table 2: ESO-HA NNN (No. 281) added.
Simbad objects:
21
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