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Published April 10, 2011 | Published
Journal Article Open

Mapping the Shores of the Brown Dwarf Desert. II. Multiple Star Formation in Taurus-Auriga


We have conducted a high-resolution imaging study of the Taurus-Auriga star-forming region in order to characterize the primordial outcome of multiple star formation and the extent of the brown dwarf desert. Our survey identified 16 new binary companions to primary stars with masses of 0.25-2.5 M_☉, raising the total number of binary pairs (including components of high-order multiples) with separations of 3-5000 AU to 90. We find that ~2/3-3/4 of all Taurus members are multiple systems of two or more stars, while the other ~1/4-1/3 appear to have formed as single stars; the distribution of high-order multiplicity suggests that fragmentation into a wide binary has no impact on the subsequent probability that either component will fragment again. The separation distribution for solar-type stars (0.7-2.5 M_☉) is nearly log-flat over separations of 3-5000 AU, but lower-mass stars (0.25-0.7 M_☉) show a paucity of binary companions with separations of ≳200 AU. Across this full mass range, companion masses are well described with a linear-flat function; all system mass ratios (q = M_(B) /M_(A)) are equally probable, apparently including substellar companions. Our results are broadly consistent with the two expected modes of binary formation (free-fall fragmentation on large scales and disk fragmentation on small scales), but the distributions provide some clues as to the epochs at which the companions are likely to form.

Additional Information

© 2011 American Astronomical Society. Received 2010 August 16; accepted 2011 January 10; published 2011 March 17. We thank Peter Tuthill and Jamie Lloyd for campaigning to have aperture masks installed in PHARO and NIRC2. We also thank Russel White for sharing the results of his multiplicity survey in Taurus prior to publication. Finally, we thank the referee for a detailed critique of this paper. A.L.K. has been supported by a SIM Science Study and by NASA through Hubble Fellowship grant 51257.01 awarded by STSCI, which is operated by AURA, Inc., for NASA, under contract NAS 5-26555. M.J.I. is supported by an Australian Postdoctoral fellowship from the Australian Research Council. This work makes use of data products from 2MASS, which is a joint project of the University of Massachusetts and IPAC/Caltech, funded by NASA and the NSF. Our research has also made use of the USNOFS Image and Catalogue Archive operated by the United States Naval Observatory, Flagstaff Station (http://www.nofs.navy.mil/data/fchpix/). We recognize and acknowledge the very significant cultural role and reverence that the summit of Mauna Kea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain.

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Published - Kraus2011p13752Astrophys_J.pdf


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