Visible Spectroscopic Observations of Flora Family

M. Florczak (Obs. Nacional/CEFET-PR, Brazil), M.A. Barucci (Obs. Paris, France), D. Lazzaro, C.A. Angeli (Obs. Nacional, Brazil), A. Doressoundiram (Obs. Paris, France), E. Dotto (Obs. Paris, France/Univ. Padova, Italy)

The Flora family was first identified by Hirayama (1919) but its existence as an unique family has been discussed eversince. Zappala et al. (1994), using a very accurate hierarchical clustering technique, found 477 memebers of the Flora family, or clan. To gain more information on the compositional distribution of the Flora family, we observed a large sample of asteroids of this family between January 1st to 8th, 1997. Forty seven reflectance spectra were obtained with a wavelenght coverage ranging from 0.49 to 0.92 tex2html_wrap_inline11 m. The observations were performed at the ESO (La Silla, Chile) using the 1.5m telescope equipped with a Boller and Chivens spectrograph and a CCD of 2048 x 2048 oixels. Reduction was perfomed using IRAF. The spectral reflectance curves of Flora family exhibit a common characteristic (except five object): a reddish spectrum with a maximum near 0.75 tex2html_wrap_inline11 m. Many asteroids have absortion band with minimum around 0.9 tex2html_wrap_inline11 m, but for most of them it is not possible to dermine precisely this minimum to the limited spectral range. Comparison with spectra obtained by other authors (Xu et al., 1995; Chapman & Gaffey, 1979) showed very similar results. Five objects have spectral behaviour different from the majority of the Flora family and we suppose they are interlopers. We interpret the continous span of the spectra found in our sample as the result of different temporal process of space wethering. This phenomena can modify the optical properties of the superficial material (Wetherill and Chapman, 1988) originating a continuos span of sligtly differnt spectra as in our data sample.

* Based on observations made with the 1.52m telescope at the European Southern Observatory (La Silla, Chile) under the agreement with the CNPq/Observatorio Nacional.