Radar observations of Asteroids 64 Angelina and 69 Hesperia

Michael K. Shepard, Alan W. Harris, Patrick A. Taylor, Beth Ellen Clark, Maureen Ockert-Bell, Michael C. Nolan, Ellen S. Howell, Christopher Magri, Jon D. Giorgini, Lance A.M. Benner

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10 Scopus citations

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 (2480MHz, 12.6cm). 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±15km, approximately 20% smaller than the reported IRAS value. We estimate Hesperia to have a radar albedo of σ̂OC=0.45±0.12, 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.

Original languageEnglish (US)
Pages (from-to)547-551
Number of pages5
JournalIcarus
Volume215
Issue number2
DOIs
StatePublished - Oct 2011
Externally publishedYes

Keywords

  • Asteroids
  • Asteroids, composition
  • Radar observations

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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