DPS Meeting, Madison, October 1998
Session 5. Asteroid Observations I
Contributed Oral Parallel Session, Monday, October 12, 1998, 9:30-10:20am, Madison Ballroom D

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[5.05] The puzzling case of the Nysa-Polana family finally solved ?

A. Doressoundiram (Torino Astronomical Observatory / JPL), A. Cellino, M. Di Martino, F. Migliorini, V. Zappala (Torino Astronomical Observatory)

We present some preliminary results of a systematic observational campaign devoted to a mineralogical characterization of the Nysa family. According to Zappalà et al. 1995 (Icarus 116, 291-314) this family is peculiar, since it splits into two major subclusters (The Nysa and the Polana sub-groups) just below the critical distance level used to define families in this region of the belt. The difficulty in assessing whether the Nysa family can be considered as a unique group or as the result of the merging of two independent families, has long prevented from undertaking systematic physical analyses of this important family. Moreover, it is known that in the region of the belt surrounding the family, there is an unusual concentration of F-type asteroids. Some of them are included into the list of nominal Nysa members, while some others apparently do not belong to the family. So far, we have observed spectroscopically 21 Nysa members. According to the obtained spectra, it seems that the Nysa and Polana subgroups are mineralogically well distinct. In particular, members of the Nysa subgroup tend to be S-type objects (with the exceptions of Nysa itself, an E-type object, and Hertha, an M-type asteroid), whereas the Polana subgroup is mostly composed of F-type objects. The implications of these results are discussed.

The author(s) of this abstract have provided an email address for comments about the abstract: alaind@mesioq.obspm.fr

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