Exploration of the Kuiper Belt by Stellar occultations

Transcription

1 Exploration of the Kuiper Belt by Stellar occultations Françoise Roques Y. Boissel, A. Doressoundiram, B. Sicardy, T. Widemann LESIA, Observatoire de Paris the occultation projects of the Paris team serendipitous occultations : a strategy of research the large telescopes research campaign results about the Kuiper Belt instrumental projects

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3 Sicardy et al. 2003

4 Varuna : 6-7 december - Namibia: Hess - Hakos: clouded out - Brazil:Pico dos Dias: clear weather,star acquired with **high SNR**, no event seen - Belo Horizonte:light curve is obtained, still awaiting processing - Uruguay: Los Molinos: very low SNR signal obtained - Aigua: no observation possible due to very low elevation - Salto: no observation due to very low elevation - UK: Elliott's place. Star easily recorded, till ice prevented any observation - Germany:Munich: clouded out - France:St-Sulpice, star observed, no event detected - Meudon: clouded out - Pic du Midi: clouded out - Spain CalarAlto : no observation

5 stellar occultations :a diffracting phenomenon What? detection of the diffraction shadow of KBOs to scan invisible small and far populations Why? : small KBO are detectable the diffraction pattern is instructive How? fast photometry large telescope Where? : target stars with small angular size

6 Occultations : the future of the Kuiper Belt? T!h!e!!o!b!s!e!r!v!e!d!!s!l!o!p!e!!o!f!!t!h!e!!l!u!m!i!n!o!s!i!t!y!!f!u!n!c!t!i!o!n!!i!m!p!l!i!e!s!!t!h!a!t!! t!h!e!!s!i!z!e!!d!i!s!t!r!i!b!u!t!i!o!n!!o!f!!t!h!e!!k!u!i!p!e!r!!b!e!l!t! i!s!!c!o!n!s!i!s!t!e!n!t!!w!i!t!h!!a!!p!o!w!e!r!-!l!a!w!!w!i!t!h!!s!l!o!p!e!!q!!=!!4!.!2!5!!±!!0!.!2!5!!f!o!r!!o!b!j!e!c!t!s!!w!i!t!h!!d!i!a!m!e!t!e!r!s!!l!a!r!g!e!r!!t!h!a!n!!d! ~!5!0!!k!m!.! Fraser et al., 2008 From the luminosity function,we have inferred the underlying size distribution and find that it is consistent with a large object power-law slope q 1 ~ 4.8 that breaks to a slope q 2 ~1.9 at object diameter D ~ 60 km assuming 6% albedos. Fraser et al., 2008 Our results have demonstrated that the size distribution of the Kuiper belt can be described by three size distribution parameters, q1, q2, and D, and that, to accurately measure the break-slope q2 requires that the radial distribution be accounted for in a way which removes the ambiguity between source brightness and source size. We have found that q1 ~ 4, q2 ~ -1, and D ~ 40 km. Fraser et al., 2008

7 Distance of the occultors Roques et Moncuquet, 2000

8 The Fresnel scale F = (λ.r/2), : λ wavelength, R: distance of the occultor R = 3 AU, F = 245 m R = 40 AU, F = 1.1 km R = 10 5 AU, F = 55 km The Fresnel scale is a scaling factor of the occultation df/f = 10% => r = 0.2 Roques et Moncuquet, 2000

9 stellar occultations : a diffracting phenomenon r< 100 meters at 50 AU : ~ 50 stars per degrees-square for a 2-m telescope

10 The t2m/photometers campaign 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

11 The large telescopes campaign The instrument : ULTRACAM an ultra-fast, triple-beam CCD camera (u : 0.36 µm, g :0.48 µm and i :0.77 µm) V. Dhillon, T. Marsh pulsars, X-ray binaries stars

12 The choice of the star

13 The data analysis : examples of false events Electronic problems Atmospheric effect

14 The data analysis 0.48 µm 0.77 µm a synthetic event: a 200 m radius object at 40 AU standard deviation (i) standard deviation (g)

15 The WHT-Ultracam results 5.6 σ 7.2 σ 5.3 σ

16 The WHT-Ultracam 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)

17 The VLT-Ultracam results Search on intervals SNR > h Doressoundiram et al., submitted

18 The VLT-Ultracam results 200m at 50 AU 2000m at 5000 AU Doressoundiram et al., submitted

19 The Ultracam campaign result : I - an object of 110m at 9-19 AU Several isolated events in the occultation lightcurves announced during the 80 s (exploration of the Uranus-Neptune systems). After, lack of fast photometric instrumentation on large telescopes For exemple: 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 august 1980 : Isolated events detected during occultation : figure 5 The 15 august 1980 Occultation by the Uranian System : Structure of the Rings and Temperature of the Upper Atmosphere, Sicardy et al., Icarus, 52,

20 The VLT-Ultracam results II - no object in the Kuiper Belt AU v. dt 3 Fsu 200 meters objects are detectable Diffracting occultation scan a surface of : ds = 10-9 R -1.5 (AU) d 2. dt(h) R=40 AU No detections in 35 h => N(200 m) < at 40 AU

21 The VLT-Ultracam results III object farther than 100AU AU A cold extented disk composed of small objects? N(200m) : (0.5 earth mass) NB : serendipitous occultations is a statistical method, The verity will come from numbers Roques et al., AJ, in press

22 Bickerton et al Doressoundiram et al., submitted

23 Then, we need more observations more observations more observations

24 ULTRACAM : an ultra-fast, triple-beam CCD camera (V. Dhillon and T. Marsh) William Herschel Telescope VLT 5 - u : 0.36 µm, g :0.48 µm and i :0.77 µm) - two fields : one target + one reference

25 G. Georgevits, M. Aschley, W. Saunders (UNSW)

26 6df/UKST Difficult data analysis : Vibrations Fibers transmission factor scintillation Georgevits et al., 2006

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28 UltraPhot :the science case : Compact pulsators in clusters : pulsating subdwarf B (sdb) stars, that are extreme horizontal branch objects with very high effective temperatures of about 30,000 K and pulsating white dwarfs belonging to the three known instability strips: DAVs or ZZ Ceti stars, DBVs and PNNV-DOVs with or without planetary nebula. periods between ~2 min and 1-2 hours Compact binaries in clusters : mapping of clusters- Cross correlation with X-ray sources : -white dwarfs, neutron stars and stellar mass black holes (time scale from second to milliseconds. On timescales of a tenth of a second, echo-tomography allow to determine the accretion geometry of cataclysmic variable and X-ray binaries (with ASTROSAT). Young Stellar Objects : UltraPhot will allow long-term monitoring of the irregular variability and survey of the variation with timescales shorter than a few hours. New database to improve our understanding of the nature of accretion processes.

29 UltraPhot la science : Exoplanets : Transit timing is a relativity new concept and few instruments exist to efficiently utilize the effect. One key desideratum for precise timing measurements is a very fast read-out from the CCD camera and today the best read-out possible is just under 1 second from the RISE instrument on the 2m Liverpool Telescope. Ultraphot offers an opportunity for two orders of magnitude better read-out frequency and therefore is ideally placed to fully exploit the transit timing effect. For Ultraphot, the timing accuracy should be at least 6 seconds per epoch, implying a resonant perturbing body could be detected in a system with 3-day period transiting hot-jupiter down to M, or 5.4 Lunar masses In addition, the potential moons of exoplanets may be also detected through timing mesurements. For example, a 1M around GJ436b would cause a 13.7 second rms amplitude and due to a linear scaling, 6 second accuracy corresponds to a 0.44 M exomoon sensitivity.

30 Stellar occultations Kuiper belt + Oort Cloud (!)

31 The VLT-Ultracam results II - no object in the Kuiper Belt AU Doressoundiram et al., submitted

32 The multi-fiber photometry concept : The first step is to upgrade MEFOS, a 29 fibers spectrograph formely at the ESO 3.6-m telescope. The project is to design a new fiber link and replace the spectrograph by a fast camera mounted on the 1.93m telescope of the Observatoire de Haute Provence (OHP, France).

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34 UltraPhot concept Ultraphot instrument is composed : A multi-object fibres link A photometer composed of : - Structure Assembly : (Bench, Interface Support ) - Slit Entrance Assembly (slits, Back Illumination, Motion Tx&Ty.) - Optics Assembly : (Relays, Mirrors, Lenses, Dichroics ) - CCD-Camera Assembly

35 Analyse UltraCam r=2.4 Sky = 15-19

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38 UltraPhot Full Frame CCD => No dead time one cycle = integration : 8.7 ms transfert+binning+reading : 1.3 ms

39 UltraPhot :scientific specifications nm spreaded in 3 colors acquisition frequency >= 100 Hz number of targets >= 100 photometric precision transmission factor > 20% input aperture on the sky >5arcsec diameter temporal and relative stability of the fibres

40 UltraPhot team Scientific PI Tecnical PI Scientific involvement Technical involvement Financial involvement Paris O.-LESIA X X X X Paris O.-GEPI X X X NTHU (Taiwan) X X X Napoli O. (Italia) X Paris O.-Luth X IAP X AAO (TBC) X Paris observatory - LESIA : F. Roques, A. Doressoundiram, Y. Boissel, B. Sicardy, J-T. Buey, M. Marteaud Paris Observatory - GEPI : I. Guinouard, D. Horville National Tsing Hua University - Department of Physics : H.-K. Chang, A. Kong, S.-P. Lai, C.-C. Hsieh Naples Observatory - INAF : D. de Martino, R. Silvotti Institut d Astrophysique de Paris : J.P. Beaulieu Paris Observatory LUTH:J. Schneider Anglo-Australian Observatory : T. Farrell, K. Shortridge ANR-NSC : 2.8 FTE

41 Budget Fibre link 50 K Mechanical 45 K Optical 30 K Camera 70K Others 15K?focal plate? Total 210 K ANR (french research agency) : 140k NSC (taiwanese research agency): 70k Planning T0 : T0 + 9 months : end of the design T0 +21 months : end of the manufacturing T months : end of integration

42 in conclusion, we need to do more observations use various telescope size - various technics - ground/space collaborate to convince of the interest of the occultation method and of fast photometry thanks very much for this workshop