[Previous] | [Session 15] | [Next]
M. Moncuquet, F. Roques (DESPA, Observatoire de Paris)
The existence of a residual protoplanetary disk beyond the Neptune orbit had been speculated by Kuiper and the recent discovery of hundreds of objects above 30 AU confirms the reality of the Kuiper hypothesis. The Kuiper Disk could include a huge number of sub-kilometer sized objects. The knowledge of this small KBOs population is a key problem because it could contain most of the Kuiper disk mass. Stellar occultations are known to be a powerful tool to explore the Outer Solar System: They led to the discovery of the Uranus and Neptune rings systems.
We explore here and in a companion paper the possibility to detect KBOs by statistical (i.e., here, unpredictable) occultations: we will show that such occultations are mainly dominated by Fresnel diffraction and that it is possible to exploite this phenomenon to optimize the detection of KBOs with high precision photometric observations. We present in the companion paper the conditions of such observations and we focus here on how the theoretical diffraction shadow of a KBO depends on its own size and shape, on the occulted star radius and on the photometric precision of the observation.
The characteristic scale of the Fresnel diffraction effect is the so-called Fresnel scale \sqrt {\lambda D/2}. The Fresnel scale at 40 AU, observed at \lambda = 0.4\mum, is 1.2 km, i.e. a KBO typical size, thereby the diffraction must be seriously taken into account to analyze the occultations. Besides the apparent radius of a star projected at 40 AU is from a fraction of kilometer to tens of kilometers, i.e. of the same order of magnitude as the KBO itself. Therefore, the lightcurve smoothing upon the star disk area must be also taken into account in our computations.
We will present modelisations of the diffraction shadow of a circular/elliptical Kuiper Belt Object, using various star radii. They show that the diffraction fringes are visible at large distance of the object (as large as the observational sensitivity is good) and that should be thus possible to detect KBOs with high precision photometric observations.
The author(s) of this abstract have provided an email address for comments about the abstract: moncuquet@obspm.fr