Physics – Optics
Scientific paper
Dec 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009aas...21441123d&link_type=abstract
American Astronomical Society, AAS Meeting #214, #411.23
Physics
Optics
Scientific paper
We present preliminary results from our astrometry program using the facility near-infrared wide-field camera WIRCam at the Canada France Hawaii Telescope (CFHT) on Mauna Kea, Hawaii. Queue scheduling at CFHT enables many brief ( 10-minute) monthly observations to be conducted very efficiently. 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. Our CFHT measurements will provide distances to ultracool binaries whose orbits we are currently monitoring with Keck laser guide star adaptive optics (LGS AO). 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. With 40 binaries ( 80 objects) in our astrometry program, we expect to double the number of ultracool binaries with parallaxes. 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, instead of using a single reference epoch.
Dupuy Trent J.
Liu Michael C.
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