Serendipitous stellar occultations and the structure of the Kuiper Belt

1. Serendipitous stellar occultations and the structure of the Kuiper Belt F. Roques, A. Doressoundiram(Observatoire de Paris) G. Georgevits (UKST, Australia) V. Dhillon (Sheffield U., UK) 1976 : An idea (Bailey) 2000 : A theory (Roques et al.) 2000-2006 :Various observational approaches : 1 - King et al. : american-taiwan project with four automatic small telescopes TAOS 2 - Roques et al. : ultra rapid camera on large telescopes WHT-VLT 3 - Alcock et al. : american project of spatial mission Whipple 2006 : Three simultaneous detections : - Chang et al.(Nature 2006) : Scorpius X1 : RXTE 58 detections - Georgevits (in press) : 100 hot stars : UKST hundreds detections - Roques et al. (AJ, 2006) : 2 very hot stars :WHT+VLT 3 detections workshop 3ieme zone 11-12 janvier 2007

2. Serendipitous stellar occultations : • What ? • detection of the shadow of kbo to scan invisible small and far populations Why ? : • the perturbation of under-kilometer kbo on occulted star flux can be detectable • How ? • fast photometry (>40 hz) • Where ? : • target stars with small angular size workshop 3ieme zone 11-12 janvier 2007

3. A diffracting phenomenon R=1 km @ 40 UA Roques and al., 2000 workshop 3ieme zone 11-12 janvier 2007

4. The Fresnel scale The Fresnel scale is the scaling factor of the occultation F = √(.R/2) • : wavelength R: distance of the kbo • R = 3 AU, Fs = 0.245 km • R = 40 AU, Fs = 1.1 km • R = 105 AU, Fs = 55 km Roques et al., 2000 workshop 3ieme zone 11-12 janvier 2007

5. Occultation profiles for different sized stars workshop 3ieme zone 11-12 janvier 2007

6. High speed photometric observations • The noise limits the possibility to detect an occultation event •  => detectable KBO • 0.1 => 430 meters KBO one meter telescope • 0.01 => 120 meters KBO four meters telescope • 0.001 => 40 meters KBO space workshop 3ieme zone 11-12 janvier 2007

7. The large telescope campaign 2004-2005 ULTRACAM is an ultra-fast, triple-beam CCD camera which has been designed “to study one of the few remaining unexplored regions of observational parameter space - high temporal resolution” (V. Dhillon). William Herschel Telescope, Canary Islands (4 meters) - 3 successive fields of 2 stars (O stars) par night - 3 wavelengths (u’: 0.36 m, g’:0.48 m and i’:0.77 m) - 44 Hz workshop 3ieme zone 11-12 janvier 2007

8. The large telescopes campaign 35 hours of data => 3 detections Roques et al.,AJ, august 2006, 132, 819 workshop 3ieme zone 11-12 janvier 2007

9. The large telescopes campaign : 0.028 distance between 100 UA and 200 UA (da = 1 UA) radius between 0 and 400 m (d = 20 m) one solution : - 320  20 meters radius - 140  1 AU distance workshop 3ieme zone 11-12 janvier 2007

10. The UKST campaignUniversity of New South wales, Australia • UKST : • 70 hours of data • - 100 stars •  = 0.4-0.8m • Hundreds of events • No diffraction fringes Georgevits, in press workshop 3ieme zone 11-12 janvier 2007

11. The UKST campaign Georgevits, in press workshop 3ieme zone 11-12 janvier 2007

12. First comparison of the UKST and the WHT results * : WHT data  : UKST data 0.2 0.3 0.5 0.7 odk radius (Fs) workshop 3ieme zone 11-12 janvier 2007

13. COROT workshop 3ieme zone 11-12 janvier 2007

14. Serendipitous stellar occultations and the structure of the Kuiper Belt First indications about the Kuiper Belt Structure : • A large population of small kbo : 1010 - 1011 odk/d2 • Extended cold disk beyond 50-200 AU • Cumulative size distribution index : q = 1.3 ? Future : spatial structure of the disk size distribution of the objects shape - binarity workshop 3ieme zone 11-12 janvier 2007