Astrophysics, abstract, astro-ph/0509401, 14 September 2005

http://arXiv.org/abs/astro-ph/0509401

Photometric Observations Constraining the Size, Shape, and Albedo of 2003 El61,
a Rapidly Rotating, Pluto-Sized Object in the Kuiper Belt

Authors: David L. Rabinowitz, Kristina Barkume, Michael E. Brown, Henry Roe,
Michael Schwartz, Suzanne Tourtellotte, Chad Trujillo
Comments: 27 pages, six figures

We present measurements at optical wavelengths of the spectral reflectance, the
rotational light curve, and the solar phase curve of 2003 EL61. With apparent
visual magnitude 17.5 at 51 AU from the sun, this newly discovered member of the
classical Kuiper Belt is now the third brightest KBO after Pluto and 2005 FY9.
Our observations reveal an unambiguous, double-peaked rotational light curve
with period 3.9154 +/- 0.0002 hours and peak to peak amplitude 0.28 +/- 0.04
mag. This is the fastest rotation period reliably determined for any body in the
solar system larger than 100 km. Assuming the body has relaxed over time to the
shape taken by a homogenous fluid body, our observations tightly constrain the
shape and density. Given the mass we recently determined for 2003 EL61 from the
orbit of a small satellite, we also constrain the size and albedo. We find a
total length of 1960 to 2500 km, a mean density of 2600 to 3340 kg m-3, and a
visual albedo greater than 0.6. We also measure a neutral reflectance at visible
wavelengths and a linear phase curve with slope varying from 0.09 mag deg-1 in
the B band to 0.13 mag deg-1 in the I band. The absolute V-band magnitude is
0.259 +/- 0.028.

DATA at http://arxiv.org/PS_cache/astro-ph/pdf/0509/0509401.pdf