Astronomy and Astrophysics – Astronomy
Scientific paper
Oct 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993a%26a...278...81r&link_type=abstract
Astronomy and Astrophysics (ISSN 0004-6361), vol. 278, no. 1, p. 81-108
Astronomy and Astrophysics
Astronomy
275
Binary Stars, Early Stars, Pre-Main Sequence Stars, Sky Surveys (Astronomy), Statistical Analysis, Visible Spectrum, Astronomical Photography, Brightness Distribution, Charge Coupled Devices, Southern Sky
Scientific paper
In an effort to determine statistical properties of visual pre-main sequence (PMS) binaries, we have carried out an extensive systematic CCD imaging survey of young low-mass stars in nearby southern dark clouds, all at about 150 pc distance. The observations were made with the European Southern Observatory (ESO) New Technology Telescope at a wavelength of 0.9 micrometers under sub-arcsecond seeing conditions. Among the 238 young stars systematically observed, we detect 37 binaries (22 new discoveries) and 1 triple system (Sz 30, also new) in the range of separations between 1 arcseconds and 12 arcseconds. Further binaries were identified outside these limits, including 6 sub-arcsec binaries. The lower limit of 1 arcseconds was imposed to ensure completeness of our sample, which we have tested through numerical simulations. Thus, we find a frequency of 16% for PMS binaries with projected separations between about 150 AU and 1800 AU. We compare these observations with the known main sequence (MS) distributions of G and K dwarfs in the same interval of separations, and find an apparent excess of PMS binaries. Under the assumption that total PMS and MS binary frequencies should be the same, the excess may imply that binary orbits undergo secular evolution towards the main sequence. We briefly discuss implications of our results for the star formation efficiency and the initial mass function. Our data suggest that in T associations binary star formation appears to be the rule, while the formation of single stars is probably the exception. We have in the same way searched for multiplicity in this extended sample. As a result, we have additionally discovered another 18 new PMS binaries and have reobserved another 32 already known PMS binaries. Therefore, in total we here provide information (component separations, brightness-ratios, and position angles) on 87 PMS binaries and 1 triple, approximately half of which are newly discovered.
Reipurth Bo
Zinnecker Hans
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