workshop 3ieme zone 11-12 janvier 2007

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 TAOS2 - Roques et al. : ultra rapid camera on large telescopes

WHT-VLT3 - 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

Roques and al., 2000

R=1 km @ 40 UA

workshop 3ieme zone 11-12 janvier 2007

4

The Fresnel scale

F = √(.R/2)

: wavelengthR: distance of the kbo

• R = 3 AU, Fs = 0.245 km• R = 40 AU, Fs = 1.1 km• R = 105 AU, Fs = 55 km

The Fresnel scale is the scaling factor of the occultation

Roques et al., 2000

workshop 3ieme zone 11-12 janvier 2007

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Occultation profiles for different sized stars

workshop 3ieme zone 11-12 janvier 2007

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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

8

The large telescope campaign 2004-2005

William Herschel Telescope,Canary Islands (4 meters)

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).

- 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

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The large telescopes campaign

Roques et al.,AJ, august 2006, 132, 819

35 hours of data=> 3 detections

workshop 3ieme zone 11-12 janvier 2007

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The large telescopes campaign :

distance between 100 UA and 200 UA (da = 1 UA)radius between 0 and 400 m (d = 20 m)

0.028

one solution :- 320 20 meters radius- 140 1 AU distance

workshop 3ieme zone 11-12 janvier 2007

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The UKST campaignUniversity of New South wales, Australia

UKST : - 70 hours of data - 100 stars- = 0.4-0.8m- Hundreds of events- No diffraction fringes

Georgevits, in press

workshop 3ieme zone 11-12 janvier 2007

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The UKST campaign

Georgevits, in press

workshop 3ieme zone 11-12 janvier 2007

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First comparison of the UKST and the WHT results

* : WHT data

: UKST data

0.2 0.3 0.70.5odk radius (Fs)

workshop 3ieme zone 11-12 janvier 2007

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COROT

Asteroseismology Field of Corot • High précision photometry • Several stars :

M 6 8 12 Sigma 4.10-4 10-3 6.10-3

60 meters objects detectable with stellar occultations i=0°

= 80° 10 days 4 detections 8 stars : 1 O5 - m=6 r = 60 m 2-30 objects 3 F5 - m=8 r = 250 m 2-12 objects 4 F5 - m=12 r = 100 m 2-12 objects

workshop 3ieme zone 11-12 janvier 2007

15

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 disksize distribution of the objectsshape - binarity