Analysis of the First Disk-resolved Images of Ceres from Ultraviolet Observations with the Hubble Space Telescope
Abstract
We present Hubble Space Telescope Faint Object Camera observations of the asteroid 1 Ceres at near-, mid-, and far-UV wavelengths (λ=3636, 2795, and 1621 Å, respectively) obtained on 1995 June 25. The disk of Ceres is well resolved for the first time, at a scale of ~50 km. We report the detection of a large, ~250 km diameter surface feature for which we propose the name ``Piazzi'' however, it is presently uncertain whether this feature is due to a crater, albedo variegation, or other effect. From limb fits to the images, we obtainsemimajor and semiminor axes of R1=484.8+/-5.1 km and R2=466.4+/-5.9 km, respectively, for the illumination-corrected projected ellipsoid. Although albedo features are seen, they do not allow for a definitive determination of the rotational motion and pole position of Ceres, particularly because of the sparse sampling (two epochs) of the 9 hr rotation period. From full-disk integrated albedo measurements, we find that Ceres has a red spectral slope from the mid- to near-UV, and a significant blue slope shortward of the mid-UV. Despite the presence of Piazzi, we detect no significant global differences in the integrated albedo as a function of rotational phase for the two epochs of data we obtained. From Minnaert surface fits to the near- and mid-UV images, we find an unusually large Minnaert parameter of k~0.9, suggesting a more Lambertian than lunar-like surface.
- Publication:
-
The Astronomical Journal
- Pub Date:
- January 2002
- DOI:
- 10.1086/338093
- arXiv:
- arXiv:astro-ph/0110258
- Bibcode:
- 2002AJ....123..549P
- Keywords:
-
- Minor Planets;
- Asteroids;
- planets and satellites: individual (Ceres);
- Ultraviolet Emission;
- Astrophysics
- E-Print:
- 9 pages, 4 figures, in AASTeX v5.02 document class with "emulateapj5" and "onecolfloat" styles (onecolfloat.sty is included). To appear in the Astronomical Journal (January 2002). Also available at http://www.boulder.swri.edu/~joel/papers.html