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ISOPHOT observations of asteroids

E. Dotto ¹, M.A. Barucci ¹, J. Crovisier ², A. Doressoundiram ³, Th. Encrenaz ¹, M. Fulchignoni ⁴, R.F. Knacke ⁵, E. Lellouch ¹, & T.G. Müller ^6,7

¹ DESPA - Observatoire de Paris, France

² ARPEGES - Observatoire de Paris, France

³ Osservatorio Astronomico di Torino, Italy

⁴ Université ``Denis Diderot'' - Paris VII, France

⁵ Penn. State University, Erie, Penn., USA

⁶ MPIA, Heidelberg, Germany

⁷ ISO SOC, Astrophysics Division of ESA, Villafranca, Spain

Observations by ISO satellite with PHT-P and PHT-S instruments have been obtained on sixteen asteroids: 1 Ceres, 2 Pallas, 3 Juno, 4 Vesta, 10 Hygiea, 52 Europa, 65 Cybele, 77 Frigga, 114 Kassandra, 308 Polyxo, 511 Davida, 624 Hektor, 911 Agamemnon, 1172 Aneas, 1437 Diomedes, and 3840 Mimistrobell.

With PHT-P we obtained the observations at filters 3.6, 10, 11.5, 25, and 60 $\mu m$ , while with PHT-S we obtained simultaneously the 2.5-5 spectral range (with resolution of about 85) and 6-12 $\mu m$ spectral range (with resolution of about 95). The 6-12 $\mu m$ part of the spectrum has been fitted with a black-body curve and the temperature has been computed for all the observed objects.

For asteroids the spectral region beyond 5 $\mu m$ is dominated by radiation thermally emitted from the bodies themselves. A thermal model has been applied to these infrared data to determine the diameter and the albedo.

A few asteroids seem to show the silicate signature around 10-11 $\mu m$ .

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"The Universe as seen by ISO", 20 - 23 October 1998, Paris: Abstract Book