AHubble Space TelescopeWide Field Planetary Camera 2 Survey for Brown Dwarf Binaries in the α Persei and Pleiades Open Clusters
- 1 September 2003
- journal article
- Published by American Astronomical Society in The Astrophysical Journal
- Vol. 594 (1), 525-532
- https://doi.org/10.1086/376938
Abstract
We present the results of a high-resolution imaging survey for brown dwarf (BD) binaries in two open clusters. The observations were carried out with WFPC2 onboard HST. Our sample consists of 8 BD candidates in the alpha Per cluster and 25 BD candidates in the Pleiades. We have resolved 4 binaries in the Pleiades with separations in the range 0".094--0".058, corresponding to projected separations between 11.7~AU and 7.2~AU. No binaries were found among the alpha Per targets. Three of the binaries have proper motions consistent with cluster membership in the Pleiades cluster, and for one of them we report the detection of Halpha in emission and LiI absorption obtained from Keck~II/ESI spectroscopy. One of the binaries does not have a proper motion consistent with Pleiades membership. We estimate that BD binaries wider than 12~AU are less frequent than 9% in the alphaPer and Pleiades clusters. This is consistent with an extension to substellar masses of a trend observed among stellar binaries: the maximum semimajor axis of binary systems decreases with decreasing primary mass. We find a binary frequency of 2 binaries over 13 BDs with confirmed proper motion membership in the Pleiades, corresponding to a binary fraction of 15%(1 sigma error bar +15%/-5%). These binaries are limited to the separation range 7-12~AU and their mass ratios are larger than 0.7. The relatively high binary frequency (>10%), the bias to separations smaller than about 15 AU and the trend to high mass ratios (q>0.7) are fundamental properties of BDs. Current theories of BD formation do not appear to provide a good description of all these properties.Comment: Accepted by ApJ (scheduled publication in volume 594, September 1, 2003Keywords
This publication has 48 references indexed in Scilit:
- Detection of Nine M8.0–L0.5 Binaries: The Very Low Mass Binary Population and Its Implications for Brown Dwarf and Very Low Mass Star FormationThe Astrophysical Journal, 2003
- Binarity in Brown Dwarfs: T Dwarf Binaries Discovered with theHubble Space TelescopeWide Field Planetary Camera 2The Astrophysical Journal, 2003
- The Ejection of Brown Dwarfs from Unstable MultiplesSymposium - International Astronomical Union, 2003
- The formation mechanism of brown dwarfsMonthly Notices of the Royal Astronomical Society, 2002
- An Adaptive Optics Survey of M8-M9 Stars: Discovery of Four Very Low Mass Binaries with at Least One System Containing a Brown Dwarf CompanionThe Astrophysical Journal, 2002
- The Substellar Mass Function in σ OrionisThe Astrophysical Journal, 2001
- Evolutionary Models for Very Low‐Mass Stars and Brown Dwarfs with Dusty AtmospheresThe Astrophysical Journal, 2000
- The Mass and Age of Very Low Mass Members of the Open Cluster α PerseiThe Astrophysical Journal, 1999
- Studies of Stellar Rotation. III. a Redetermination of Rotational Velocities in the PleiadesThe Astrophysical Journal, 1966
- The Frequency of Spectroscopic Binaries in the Pleiades.The Astrophysical Journal, 1965