Physics – Optics
Scientific paper
Jan 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009aas...21340617d&link_type=abstract
American Astronomical Society, AAS Meeting #213, #406.17; Bulletin of the American Astronomical Society, Vol. 41, p.201
Physics
Optics
1
Scientific paper
We present preliminary results from our infrared astrometry program using the wide-field camera WIRCam at the Canada France Hawaii Telescope (CFHT) on Mauna Kea, Hawaii. Our program is ideal for measuring parallaxes to ultracool dwarfs (i.e., late-M, L, and T dwarfs) because: (1) ultracool objects are brightest in the near-infrared (JHK) (2) the effect of differential chromatic refraction (DCR) is reduced at longer wavelengths; (3) the exceptional seeing on Mauna Kea leads to high astrometric precision; (4) the queue scheduling available at CFHT enables many brief ( 10-minute) monthly observations to be conducted very efficiently. We are currently monitoring the orbits of a large sample of ultracool visual binaries using Keck laser guide star adaptive optics (LGS AO), and our CFHT measurements will provide distances to these binaries. Precise distances are crucial for measuring precise dynamical masses since Mtot d3α3P-2 (Kepler's 3rd Law, where α is the angular semimajor axis). Although the shortest period ultracool binaries are nearby enough to have precisely measured distances (d < 30 pc), most ( 4/5) have no parallax measurements to date because previous programs did not specifically target binaries. Analysis of our WIRCam data spanning > 1 year demonstrates our ability to measure parallaxes to 1-3 milliarcsec (i.e., distances to 3-5%). Our measurements for objects with known parallaxes are consistent with the published values, validating this preliminary analysis. We also present a novel method for finding the best-fit parallax and proper motion that fully exploits all independently measured positional offsets between every pair of observation epochs, weighting all epochs equally instead of using a single reference epoch.
Dupuy Trent J.
Liu Michael C.
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