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Radar observations of Asteroids 64 Angelina and 69 Hesperia |
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| Authors: | Michael K Shepard Alan W Harris Beth Ellen Clark Michael C Nolan Christopher Magri Lance AM Benner |
| Institution: | a Bloomsburg University, 400 E. Second St., Bloomsburg, PA 17815, USA b Space Science Institute, La Cañada, CA 91011-3364, USA c NAIC/Arecibo Observatory, HC 3 Box 53995, Arecibo, PR 00612, USA d Ithaca College, Ithaca, NY 14853, USA e University of Maine at Farmington, Farmington, ME 04938, USA f Jet Propulsion Laboratory, Pasadena, CA 91109, USA |
| Abstract: | We report new radar observations of E-class Asteroid 64 Angelina and M-class Asteroid 69 Hesperia obtained with the Arecibo Observatory S-band radar (2480 MHz, 12.6 cm). Our measurements of Angelina’s radar bandwidth are consistent with reported diameters and poles. We find Angelina’s circular polarization ratio to be 0.8 ± 0.1, tied with 434 Hungaria for the highest value observed for main-belt asteroids and consistent with the high values observed for all E-class asteroids (Benner, L.A.M., Ostro, S.J., Magri, C., Nolan, M.C., Howell, E.S., Giorgini, J.D., Jurgens, R.F., Margot, J.L., Taylor, P.A., Busch, M.W., Shepard, M.K. 2008]. Icarus 198, 294-304; Shepard, M.K., Kressler, K.M., Clark, B.E., Ockert-Bell, M.E., Nolan, M.C., Howell, E.S., Magri, C., Giorgini, J.D., Benner, L.A.M., Ostro, S.J. 2008b]. Icarus 195, 220-225). Our radar observations of 69 Hesperia, combined with lightcurve-based shape models, lead to a diameter estimate, Deff = 110 ± 15 km, approximately 20% smaller than the reported IRAS value. We estimate Hesperia to have a radar albedo of  , consistent with a high-metal content. We therefore add 69 Hesperia to the Mm-class (high metal M) (Shepard, M.K., Clark, B.E., Ockert-Bell, M., Nolan, M.C., Howell, E.S., Magri, C., Giorgini, J.D., Benner, L.A.M., Ostro, S.J., Harris, A.W., Warner, B.D., Stephens, R.D., Mueller, M. 2010]. Icarus 208, 221-237), bringing the total number of Mm-class objects to eight; this is 40% of all M-class asteroids observed by radar to date. |
| Keywords: | Asteroids Asteroids Composition Radar observations |
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