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ASTEP : lessons from OGLE
Frédéric Pont
Geneva Observatory
7 transiting exoplanets found by photometric surveys:
OGLE-TR-10, OGLE-TR-56, OGLE-TR-111, OGLE-TR113, OGLE-TR-132
TrES-1
XO-1
The OGLEIII exoplanet transit survey
Dedicated 1.3m telescope
8k x 8k mosaic
0.34 deg2 field-of-view
Warsaw tel. (Las Campanas, Chile)
PI Andrzej Udalski
5 seasons
~25 fields
15-18th magnitude
~500’000 targets
~1000 meas/target
~250 nights of observation
262 planetary transit candidates
FLAMES/FORS follow-up of OGLE candidates
Francois Bouchy, Frédéric Pont, Nuno Santos, Didier Queloz,
Claudio Melo, Stephane Udry, Michel Mayor, Claire Moutou
FLAMES : 7-fiber link to high-resolution spectro
UVES on the VLT
FORS : high-resolution camera on the VLT
Nature of OGLE planetary transit candidates
Transiting gas giant planets
[5]
Eclipsing binaries
[>20]
- grazing
- low-mass companion
[>100]
- multiple systems and blends
[>50]
False positive of the transit detection
[10-20]
OGLE: what could we expect?
Typical season : ~ 60 nights of observations  15 x 24hours
Typical hot Jupiter P ~ 3-4 days  3-5 transits sampled
Typical OGLE uncertainty 5 mmag, ~ 10 points in each transit
 30 - 50 points in transit
 uncertainty on transit depth 5/sqrt(30-50) ~ 0.5 mmag
Typical hot Jupiter transit depth 1% = 10 mmag
easy detection, ~20 
5 seasons x 30’000 suitable targets x 0.1% transit probability =
150 detectable transiting Hot Jupiters.
OGLE: what did we find?
Period
Depth
Ntransits
OGLE-TR-10
3.10
1.9 %
7
OGLE-TR-56
1.21
1.3 %
12
OGLE-TR-111
4.01
1.9 %
9
OGLE-TR-113
1.43
3.0 %
10
OGLE-TR-132
1.69
1.1 %
11
(Normal Pegasid
4.3
1.0 %)
3-5
Five “anomalous” planets
Cause of low yield of transit surveys ?
Fluctuations in the photometry
X
Time coverage
Period [days]
Detection probability
Cause of low yield of transit surveys ?
Fluctuations in the photometry
X
Time coverage
ANTARCTICA
A STEP