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P. Rousselot, J.M. Petit (Obs. Besancon, France)
We observed three Centaurs (2000 EC98, 2000 GM137 and 2000 FZ53) in imaging mode with the 3.5 m New Technology Telescope (NTT) of the European Southern Observatory (ESO), located in Chile. We obtained different series of images on 26 and 27 April 2001, with broad band filters (mainly R and also V and B). The integration time of individual images was short (80 to 205 seconds) to avoid smearing due to the proper motion of the Centaurs. The different series of images have been shifted according to the rate of motion of each object, so that it has been possible to co-add them and to extract a single image of each Centaur. The resulting images obtained have been used to compute the radial profil of each target (magnitude/arcsec2 vs radial distance from the centroid in arcsec). The different profiles being compared with that of a bright star obtained with the same images and normalized at the same intensity.
Preliminary results seem to indicate that the brightest of the three objects (2000 EC98, magR ~21) show no evidence of cometary activity down to magnitude ~ 27/arcsec2, the maximum intensity being 21.2 mag./arcsec2. Due to bad seeing, we obtained only 31 minutes worth of usable data on 2000 FZ53 (magR ~ 23). With a central magnitude of ~23/arcsec2 and a large noise, no conclusion can be drawn for this Centaur. For 2000 GM137 (magR ~22.5) on the contrary, preliminary data processing is compatible with a small coma of magnitude ~25.5 - 26/arcsec2 at ~1 - 2 arcsec. However, the noise level of the observations is too high to permit any final conclusion. More data processing and observations are definitely needed.
Some classical photometric results (R magnitudes and color indices) can also be derived from the observations and will be presented.