Observation and Analysis of a Single-Chord Stellar Occultation by Kuiper Belt Object (50000) Quaoar

The Williams-MIT collaboration (www.stellaroccultations.info) predicted and observed a stellar occultation of 2UCAC 26260847 (mag 14.35) by KBO 50000 Quaoar (mag 18.9) on 8/9 July 2013. Observations were attempted from a total of five sites in Chile, Venezuela, and Massachusetts. Only one site, Llano del Hato National Astronomical Observatory in Venezuela, had a positive detection of the occultation, giving us a single chord on Quaoar. All other sites were cloudy. The light curve from the 8/9 July 2013 event has been analyzed with the assumption that Quaoar is ellipsoidal or spherical, placing bounds on some of Quaoar’s properties: diameter (> 1138 ± 25 km), density (< 1.82 ± 0.28 g cm_-3), and albedo (< 0.14 ± 0.10). An independent prediction of the occultation’s shadow path by Fraser, Gwyn, et al. (2013) suggests that the chord is near-equatorial, which means that our bounds on Quaoar’s properties are closer to estimates. We will compare our result with that of the 11 February 2011 single-chord occultation detected by Sallum et al. (2011) and Person et al. (2011). A subsequent attempt to observe a second Quaoar occultation, that of 12/13 July 2013 in South Africa, failed because of cloudy weather. This work was supported in part by NASA Planetary Astronomy grants NNX08AO50G and NNH11ZDA001N to Williams College, NNX10AB27G to MIT, and USRA grant #8500-98-003 to Lowell Observatory. We thank Steven P. Souza at Williams, and other collaborators in planning and carrying out the various observations: including Libardo Zerpa, Joresly Villarreal, Richard Rojas, and Jorge Moreno at Llano del Hato, and Patricio Rojo and Matias Jones at Cerro Calan/U. Chile.