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Improving the Distortion Solution for Brown Dwarf Parallax Measurements from the Canada-France-Hawaii Telescope

Presentation #222.03 in the session Exoplanets Formation & Evolution (Poster + Lightning Talk)

Published onOct 23, 2023
Improving the Distortion Solution for Brown Dwarf Parallax Measurements from the Canada-France-Hawaii Telescope

Brown dwarfs have a degenerate relationship between mass, age, and luminosity; a young, low mass brown dwarf can have the same luminosity, temperature, and spectral type as an older, more massive brown dwarf. Such degeneracy makes modeling their evolution difficult and even sophisticated models, such as (Saumon and Marley 2008, ApJ, 689, pp. 1327), do not account for all spectral types. Parallax distances are needed to better constrain these models since they are required to determine the dynamical masses of binary systems, bolometric luminosities, and approximate ages. As part of the Hawaii Infrared Parallax Program, high-precision parallax measurements have been made using the Canada-France-Hawaii Telescope (CFHT) since 2007 and efforts have been ongoing (e.g. Dupuy & Liu 2012, ApJS, 201, id.19). However, some brown dwarfs do not have enough field stars with known positions to calculate an astrometric solution. In these cases, distortion limits the precision of the astrometry. Here, we present a new distortion solution for the Wide-field InfraRed Camera (WIRCam). We imaged a calibration field that contains roughly 1,700 stars in the H2 filter and roughly 5,000 stars in the J filter, many of which have Gaia astrometric measurements. Altogether, 1,918 images were taken from 2011 to 2021 and in total we matched about 4 million sources in the field to stars in Gaia. We measured the systematic offset between our calculated astrometric positions and those reported in Gaia as a function of pixel location on the detector. This distortion solution will not only allow for higher-precision parallax measurements, but will aid the search for new ultracool objects, astrometric perturbations, and associations with moving groups. It could also be useful for astrometric measurements of solar system objects in relatively sparse fields. The solution will be released publicly as part of a Python software package suitable for a wide range of applications.

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