First detection of small Kuiper objects by stellar occultations

The formation of planets in the circumsolar disc left debris beyond planets, the disc of Kuiper. Hundreds of objects of a few hundreds to a few tens of kilometers were discovered beyond the orbit of Neptune since 1992. The largest known at present, Eris, 2400 km in diameter, is even a little larger than Pluto (2300 km). Several of these objects are, like Pluto, in resonance with Neptune. These discoveries led the IAU to retrogress Pluto from "a planet" statute to "a dwarf planet" statute. However, the structure of this disc is very badly known because the majority of the objects composing it are too small or too remote to be observed. The technique of stellar occultations, which proved efficient to discover the rings of Neptune or the atmosphere of Pluto, has just allowed this international team to detect, for the first time, Kuiper objects invisible by other methods. These observations were carried out from April 2004 at the Telescope William Herschel of the Canaries equipped with high-speed camera ULTRACAM from the team of professors Dhillon and Marsh from the Universities of Sheffield and Southampton. These observations allowed the detection of three objects. Two of these detections correspond to objects of about 300 meters located at more than 100 astronomical units from the Earth.

Figure 1 : Simulation of an occultation. The principle of the experiment is to record the flux of the star at a very high frequency (typically 100 Hz) in order to detect the passage of objects in front of the star. This technique is sensitive to the presence of objects of a few hundreds of meters at the boundary of the solar system. If the star has an apparent diameter small enough, the profile of the occultation is a diffracting phenomenon, i.e. the shadow of the object on the Earth has not the sharp shape of the object but presents diffraction rings, that the telescope detects as stellar flux fluctuations, at the ring crossings

Other observations, from an Australian team and a Taiwanese team, are currently being analysed, and could confirm these detections. These detections let think that the disc of Kuiper contains billion of objects of size lower than a kilometer in a cold and very wide disc. Systematic observations based on this method will allow to discover the radial and vertical structure of the Kuiper disc.

Reference

• Exploration of the Kuiper Belt by High Precision Photometric Stellar occultations : First Results. F. Roques, A. Doressoundiram, V. Dhillon, T. Marsh, S. Bickerton, JJ Kavelaars, M. Moncuquet, M. Auvergne, I. Belskaya, , M. Chevreton, F. Colas, A. Fernandez, A. Fitzsimmons, J. Lecacheux, O. Mousis, S. Pau, N. Peixinho, G.P. Tozzi, 2006, AJ, 132, 819-822

Dernière modification le 21 décembre 2021