This work is the first exploration of the physical properties of the irregular Uranian satellites. Sycorax appears to be a very interesting object: the overall shape of its spectrum is very curious, and does not look like what we expected to find since its visible colors were very close to those of TNOs and Centaurs. Does what we found really correspond to the composition of Sycorax surface? Or is it due to some kind of rotational effect? From our data, a strong change in the magnitude may explain the observed shape of the spectrum. But the rotational period is still unknown, so we are unable to say if it occurred. A more complete investigation of Sycorax is absolutely required to better understand this satellite.
For the moment, Sycorax is the only one of the irregular Uranian satellites that can be fully studied with photometry and spectroscopy techniques. The four other satellites are fainter than 23th magnitude, so spectroscopic observations cannot be carried out, even with the largest telescopes available. But the knowledge of their colors and rotational periods could help us in constraining the possible links between these five satellites.
Acknowledgements
We would like to thank E. Le Floc'h for fruitful discussions about near-infrared data reduction.
Copyright ESO 2001