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Published April 2004 | Published
Journal Article Open

Direct Measurement of the Size of the Large Kuiper Belt Object (50000) Quaoar


We imaged the recently discovered bright Kuiper belt object (50000) Quaoar with the Hubble Space Telescope High Resolution Camera to directly determine its size. The point-spread function (PSF) of each of 16 images was carefully measured from a field star 13" from Quaoar, and the expected PSF at the location of Quaoar was convolved with Quaoar's motion vector and a model resolved disk. A least-squares analysis was performed to find the best-fit disk size. The apparent diameter of Quaoar was resolved as 40.4 ± 1.8 milliarcseconds. Accounting for the uncertainty due to an unknown limb-darkening function, the size of Quaoar is 1260 ± 190 km with red and blue albedos of 0.092^(+0.036) _(-0.023) and 0.101^(+0.039)_(-0.024), respectively. These albedos are significantly higher than the canonically assumed value of 4%. Quaoar is the largest currently known minor planet.

Additional Information

© 2004 American Astronomical Society. Received 2002 October 7; accepted 2003 December 23. We would like to thank the director and staff at STScI for providing the opportunity to make these measurements and the assistance in making them happen. In particular, without prodding from Ian Griffin we would not have taken this second set of data, which allowed us to shrink the random-error bars by a factor of 6. We would also like to thank John Krist for his excellent comments as a referee for this paper. This research has been supported by grant GO-9678 from STScI and by NASA Planetary Astronomy.

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