Trans Neptunian Objects

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

1. a diffracting phenomenon
2. a strategy of research
3. the large telescopes research campaign
4. results about the Kuiper Belt

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

3
stellar occultations a diffracting phenomenon

• The strategy
• search for the smallers
• KBO
• ponctual stars
• very few target stars
• high frequency

4
The Fresnel scale

• R 3 AU, F 245 m
• R 40 AU, F 1.1 km
• R 105 AU, F 55 km

F v(?.R/2)

• wavelength
• R distance of the occultor

The Fresnel scale is a scaling factor of the
occultation
dF/F 0.1 gt r 0.2
Roques et Moncuquet, 2000
5
The distance of the occultor
For objects lt 0.7, the size of the shadow is
almost constant
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. v(?.R/2) v E .(cos(?)-R-1/2). dt
• direct estimation of R

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
• gt first constraint on the size
• Distribution q lt 4.5

one potential event (r150m)
Roques et al., 2003
8
The large telescopes campaign 2004-2006
The instrument ULTRACAM an ultra-fast,
triple-beam CCD camera (u 0.36 ?m, g0.48 ?m
and i0.77 ?m) Vik Dhillon (U. Sheffield) Tom
Marsh (U. Southampton)
pulsars, X-ray binaries stars
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)

10
The data
Tycho 2 ref. V magn. Radius at 40AU Ecliptic latitude
281-906 12.29 80 m 2.9
281-864 12.15 250 m
6172-1154 12.70 90 m -0.4
6172-1103 11.81 270 m
6821-1317 12.25 70 m -7.1
6821-1425 12.40 100 m

• data S/N
• WHT 40 to 72
• VLT 50 to 160

gt dF/F 0.1 gt 4.?
11
The data analysis
Electronic problems
Atmospheric effect (Dravins et al., 1977)
Examples of false events
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)
13
The results
In 35 h of data, 3 events with deviation larger
than 5??
5.6 ? 7.2 ? 5.3 ?
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
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)

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
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) d2. dt(h)

No detections in 35 h gt N(200 m) lt 4. 1013 at 40
AU less than 0.2 earth mass in the KB
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
19
Conclusions

• More observations
• more observations
• more observations
• and also
• more wavelengths
• more diffraction fringes !