The invisible Kuiper Belt explorated by stellar occultations

1. The invisible Kuiper Belt explorated by stellar occultations Françoise Roques Observatoire de Paris A. Doressoundiram, M. Moncuquet M. Auvergne, M. Chevreton, F. Colas, J. Lecacheux, S. Pau, I. Belskaya, N. Peixinho, G.P. Tozzi, O. Mousis a diffracting phenomenon a strategy of research the large telescopes research campaign results about the Kuiper Belt Trans Neptunian Objects Dynamical and Physical properties

2. stellar occultations :a diffracting phenomenon • What ? • detection of the diffraction shadow of KBOs to scan invisible small and far populations Why ? : • the perturbation of small KBO on the occulted star flux can be detectable • the diffraction shadow is larger than the geometrical shadow • How ? • fast photometry • large telescope • Where ? : • target stars with small angular size Trans Neptunian Objects Dynamical and Physical properties

3. stellar occultations :a diffracting phenomenon • The strategy : • search for the smallers • KBO • ponctual stars • very few target stars • high frequency Trans Neptunian Objects Dynamical and Physical properties

4. The Fresnel scale • R = 3 AU, F = 245 m • R = 40 AU, F = 1.1 km • R = 105 AU, F = 55 km F = √(.R/2) • : wavelength R: distance of the occultor The Fresnel scale is a scaling factor of the occultation dF/F = 0.1 => r = 0.2 Roques et Moncuquet, 2000 Trans Neptunian Objects Dynamical and Physical properties

5. The distance of the occultor For objects < 0.7, the size of the shadow is almost constant Trans Neptunian Objects Dynamical and Physical properties

6. The distance of the occultor If the observations detect 0.2 radius occultors… • The shadow diameter is 3 (in Fresnel scale!) • The event duration dt drives to the distance of the occultor R: hypothesis 1 : the impact parameter is 0 : 3. F = vo. dt hypothesis 2 : the occultor orbit is circular : vo= vE .(cos()-R-1/2) 3.√(.R/2) = v E .(cos()-R-1/2). dt • direct estimation of R Trans Neptunian Objects Dynamical and Physical properties

7. The T-2M campaign2000-2003 • Observations on Bernard Lyot Telescope with multi-objects • photometers • field : 2 targets + 1 reference star • 20 Hz • 15h with S/N = 55 • strategy : search for dips in the • ligthcurve • => first constraint on the size • Distribution :q < 4.5 one potential event (r=150m) Roques et al., 2003 Trans Neptunian Objects Dynamical and Physical properties

8. The large telescopes campaign 2004-2006 The instrument : ULTRACAM an ultra-fast, triple-beam CCD camera (u’: 0.36 m, g’:0.48 m and i’:0.77 m) Vik Dhillon (U. Sheffield) Tom Marsh (U. Southampton) pulsars, X-ray binaries stars… Trans Neptunian Objects Dynamical and Physical properties

9. The large telescopes campaign The may 2004 observations WHT,Canary Islands (4 meters) - 3 successive fields of 2 stars (O stars) - 44 Hz - 4 nights The may 2005 observations VLT (8 meters) - 2 fields of 2 stars (O stars) - 68 Hz - 2 nights • The march 2006 observations • WHT,Canary Islands (4 meters) • - 3 successive fields of 2 stars (O stars) • 68 Hz • 4 nights • (under analysis) Trans Neptunian Objects Dynamical and Physical properties

10. The data • data S/N : • WHT : 40 to 72 • VLT : 50 to 160 =>dF/F =0.1 > 4. Trans Neptunian Objects Dynamical and Physical properties

11. The data analysis Electronic problems Atmospheric effect (Dravins et al., 1977) Examples of false events Trans Neptunian Objects Dynamical and Physical properties

12. The data analysis 0.48 m A synthetic event: a 200 m radius object at 40 AU 0.77 m standard deviation (i) standard deviation (g) Trans Neptunian Objects Dynamical and Physical properties

13. The results In 35 h of data, 3 events with deviation larger than 5 : 5.6  7.2  5.3  Trans Neptunian Objects Dynamical and Physical properties

14. The results Fit with the hypothesis 1 and 2 R : 100 AU and 200 AU  : 0 and 400 m 320  20 meters radius 140  1 AU distance Trans Neptunian Objects Dynamical and Physical properties

15. The results Several cheks have been run to asses the validity of the detections : • Comparison star • The color signature • Check the star position • Chech the sky glitches • Search in randomized data • Search for events in the ligthcurve of a large star (occultations by Uranus and Neptune of stars with radius larger than 10 km at 40 AU) Trans Neptunian Objects Dynamical and Physical properties

16. I - an object of 110m at 9-19 AU More dark matter around Saturn and Uranus? 22 avril 1982 : during an occultation par Uranus, an event has been observed simultaneously with two nearby telescopes. compatible with a 1.4 km diameter object More dark matter around Uranus and Neptune?, Sicardy et al., Nature 1986 Trans Neptunian Objects Dynamical and Physical properties

17. II - no object in the Kuiper Belt30-60 AU 200 meters objects are detectables Diffracting occultations scan a surface of : dS = 10 -9 R-1.5(AU) d°2. dt(h) No detections in 35 h => N(200 m) < 4. 1013 at 40 AU less than 0.2 earth mass in the KB Trans Neptunian Objects Dynamical and Physical properties

18. III - 1-2 object farther than 100AU115 - 225 AU A cold extented disk composed of small objects ? N(200m) : 10 14 (0.5 earth mass) NB : serendipitous occultations is a statistical method, The physical reality will com from “numbers” Roques et al., AJ, in press Trans Neptunian Objects Dynamical and Physical properties

19. Conclusions • More observations • more observations • more observations … • and also • more wavelengths • more diffraction fringes ! Trans Neptunian Objects Dynamical and Physical properties