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J. Romon, C. de Bergh, M. A. Barucci (Observatoire de Paris), J.-G. Cuby (ESO, Chile), A. Le Bras (Observatoire de Paris)
We have started an observing program of the recently discovered Uranian satellite Sycorax (S/1997 U 2), including both photometry and spectroscopy. Dynamical studies suggest that some irregular satellites could be captured objects (see eg. Pollack et al., Icarus, 37: 587-611, 1979). Thus, studying the irregular satellites of the giant planets is of great interest because of possible relationships with asteroids and comets. In particular, irregular satellites of Uranus and Neptune could be linked to the Trans-Neptunian and Centaur populations. Photometric observations performed at the time of the discovery gave a first estimate of the broad-band colors in BRI bands (Gladman et al., Nature, vol. 392, 1998). On the basis of these data, Sycorax appears to be nearly as red as the reddest objects of the Kuiper Belt. A better knowledge of the physical and chemical properties of this satellite, which requires to obtain a more complete data set, could help in constraining and understanding the possible link of Sycorax with the Kuiper Belt objects. As Sycorax is a faint object (V magnitude of about 20), it is very difficult to observe, and large telescopes are required. To date, we performed infrared photometry (in H and K bands) and J band spectroscopy at the VLT (ESO, Chile) with the ISAAC spectrometer. We also plan to obtain visible colors and H and K-band spectra. We will present the current status of our observing program. Our first results seem to confirm the redness of this object, but we also found a decrease of the slope in the near-IR. The same kind of behaviour has already been observed in some Trans-Neptunian objects.
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