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B. Macintosh (LLNL), B. Zuckerman, D. Kaisler, E.E. Becklin, P. Lowrance, R. Webb (UCLA), S. Olivier, C.E. Max (LLNL)
Several dozen extrasolar planets are now known, all detected through radial velocity variations induced in their parent stars. Though powerful, the radial velocity technique is most sensitive to objects in close orbits and measures only the mass and orbit of the planet, not its other properties. Other indirect techniques such as astrometry will have similar limitations.
The direct detection of photons emitted by extrasolar planets, particularly those in wide orbits, is potentially a powerful complement to indirect techniques. The halo of scattered light that surrounds a bright star makes this extremely challenging, but adaptive optics (AO) on 8-10 m telescopes brings this possibility into reach. The first such large-telescope AO system has been operating on the 10-m W.M. Keck II telescope since 1999. Keck AO is now capable of detecting objects at contrast ratios as high as 106 at separations of 1-2 arcseconds.
A mature Jupiter-like planet is approximately 109 times dimmer than its parent star, undetectable at the current time. However, a young (10 MYr) Jupiter-mass planet retains enough heat to radiate brightly in the near- infrared, making it only 105 times dimmer than a star. We are carrying out a search for such planetary companions to young nearby stars, including members of the TW Hydrae association. Initially we have been following up candidate companions discovered by NICMOS, including the brown dwarf TWA5B. Our observations of TWA5B confirm its companionship and therefore its brown dwarf nature. In addition, TWA5A is resolved as an 0.06 arcsecond double, opening up the possibility of precise mass determinations for this young system. I will discuss followup observations of other candidates and the current sensitivity limits and limitations of our search.
This research was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract W-7405-ENG-48, and also supported in part by the Center for Adaptive Optics under the STC Program of the National Science Foundation.
The author(s) of this abstract have provided an email address for comments about the abstract: bmac@igpp.ucllnl.org