Charon's Radius and Atmospheric Constraints from the 2005 July 11 Stellar Occultation

Details Charon's Radius and Atmospheric Constraints from the 2005 July 11 Stellar Occultation Charon's Radius and Atmospheric Constraints from the 2005 July 11 Stellar Occultation

Dec 2005

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005dps....37.5505g&link_type=abstract

American Astronomical Society, DPS meeting #37, #55.05; Bulletin of the American Astronomical Society, Vol. 37, p.1571

Astronomy and Astrophysics

Astronomy

Scientific paper

On 2005 July 11 (UT), Charon occulted the star ``C313.2" (originally identified as a Pluto occultation star [McDonald & Elliot, Astron. J. 120, 1599, 2000]; UCAC2 26257135; R = 14.8). We arranged to observe this event using five telescopes at four sites: the 0.6-m at Pico dos Dias Obs. (Brazil), the 0.84-m at Obs. Cerro Armazones, the 2.5-m du Pont and 6.5-m Clay at Las Campanas Obs., and the 8-m Gemini South at Cerro Pacha (Chile). The observations were successful at all stations excluding Pico dos Dias, which was clouded out.
The Acquisition Camera was employed at Gemini South, while the remaining sites used POETS (Portable Occultation, Eclipse, and Transit Systems). Each system utilized a high-speed camera, a control computer, and a GPS to establish accurate timing. The cameras contain back-illuminated CCDs, with > 90% quantum efficiency, ˜ 6 electrons read noise, and 1.74 ms deadtime during frame transfer. For this event, data rates were 2 - 10 Hz and signal-to-noise ratios were 28 - 273 (normalized to 1 s). The Clay telescope light curve had high enough time resolution and signal-to-noise to detect the first diffraction fringe.
This dataset marks significant improvement over the only previously viewed stellar occultation by Charon (Walker, MNRAS 192, 47, 1980; Elliot & Young, Icarus 89, 244, 1991). By fitting the light curves with models derived from French and Gierasch (Astron. J. 81, 445, 1976), we have calculated Charon's radius and placed strong constraints on an atmosphere. These results seem consistent with a collisional origin of the Pluto-Charon system in which either of the precursor bodies may have been differentiated (McKinnon, Astrophys. J. Lett. 344, L41, 1989).
Support provided, in part, by NASA Planetary Astronomy grants NNG04GE48G, NNG04GF25G, and NNH04ZSS001N, IAP P5/36 of the Belgian Federal Office, and BIL 01/3 of the Flemish Ministry.

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