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M.A. Barucci (Obs. de Paris), J. Romon (Obs. de Paris), A. Le Bras (Obs. de Paris), M. Fulchignoni (Obs/Univ of Paris), D. Tholen (Univ. of Hawaii)
The physical and chemical properties of Trans-Neptunian Objects (TNO) are still poorly known because of the intrinsic faintness of these objects. Tegler and Romanishin (1998) analysing B-V vs V-R distributions for 9 TNO and 4 Centaurs, found that their sample were separated in two groups, one neutral and the other very red. Barucci et al (1999) analysing the 3 dimentional distribution (B-V, V-R, R-I) of 22 TNO, found that the population of these objects is more complex and inhomogeneous.
To investigate the physical properties of Trans Neptunian objects, we are continuing the TNO observational program at the European Southern Observatory with the 3.6 m Telescope (NTT). In 1999 B,V,R,I data have been obtained for eight new objects: 1997 CQ29, 1997 CU29, 1997 CS29, 1997 CT29, 1993 FW, 1995 HM5, 1998 WH24 and 1998 FS144. These new data will increase the available statistical sample and will allow us to have a better understanding of the TNO's modification surface mechanisms.
To obtain observations with good signal to noise ratio are extremely difficult and requires considerable telescope resources as well as very careful data reduction and calibration.