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Low-mass binaries in the young cluster IC 348: implications for binary formation and evolution *
G. Duchêne 1,
J. Bouvier 1 and
T. Simon 2
Received 16 November 1998 / Accepted 4 January 1999
We report on a near-infrared adaptive optics survey of a sample of 66 low-mass members of the pre-main sequence stellar cluster IC 348. We find 12 binary systems in the separation range -, excluding 3 probable background projected companions. An estimate of the number of faint undetected companions is derived, before we evaluate the binary frequency in this cluster. In the range 5.0-7.9 days, the binary fraction in IC 348 is %. This is similar to the values corresponding to G- and M-dwarfs in the solar neighbourhood population (% and %, respectively). Furthermore, the distribution of orbital periods of IC 348 binaries in this range is consistent with that of field binaries. We conclude that there is no binary excess in IC 348.
Substellar companions are found to be rare, or even missing, as companions of low-mass stars in the separation range we surveyed. Also, the mass ratio distribution is not peaked at in IC 348, and it is unlikely that an observational bias can account for that.
We do not find any evidence for an evolution of the binary frequency with age within the age spread of the cluster of about 10 Myr. Comparing the binary frequency in IC 348 with that of other star forming regions (SFRs) and young open clusters, we conclude that there is no significant temporal evolution of the binary fraction between a few Myrs after the formation process and the zero-age main sequence (ZAMS) and field populations. We find instead a trend for the binary fraction to be inversely correlated with stellar density, with dense clusters having a binary fraction similar to that of field dwarfs and loose associations exhibiting an excess of binaries. Two scenarios can be suggested to explain these differences: either all SFRs, clusters and associations alike, initially host a large number of binaries, which is subsequently reduced only in dense clusters on a timescale of less than 1 Myr due to numerous gravitational encounters, or specific initial conditions in the parental molecular clouds impact on the fragmentation process leading to intrinsically different binary fractions from one SFR to the other.
Key words: stars: binaries: visual stars: formation stars: imaging stars: pre-main sequence Galaxy: open clusters and associations: individual: IC 348 infrared: stars
* Based on observations made with the Canada-France-Hawaii Telescope, operated by the National Research Council of Canada, the Centre National de la Recherche Scientifique de France and the University of Hawaii
Send offprint requests to: G. Duchêne
Online publication: March 1, 1999