A STEP
Antarctica Search for Transiting
Extrasolar Planets
F.Fressin, T.Guillot
Y.Rabbia, A.Blazit, JP. Rivet, J.Gay, D.Albanese, V.Morello, N.Crouzer (OCA - Nice),
F.X Schmider, K.Agabi, J-B. Daban, E.Fossat,
L.Abe, C.Combier,F.Janneaux,Y. Fantei (LUAN – Nice)
C.Moutou, F.Bouchy, M.Deleuil, M.Ferrari, A.Llebaria, M.Boer, H.Le Corroler,
A.Klotz,A.Le van Suu,J. Eysseric, C Carol (OAMP - Marseille),
A.Erikson, H.Rauer (DLR - Berlin),
F.Pont (Obs. Genève)
The future of transit searches
Combined to radial-velocimetry, it is
the only way to determine the
density, hence the global composition
of a planet
Transit spectroscopy offers
additional possibilities not accessible
for “normal” planets
We foresee that exoplanetology
will have as its core the study of
transiting exoplanets
examples:
A correlation between the metallicity of stars
and planets (Guillot et al. A&A 2006)
Planetary formation model constraints
(Sato et al 2005)
The future of transit searches
2 future milestones:
•COROT: 60 000 stars (nominal mission), mv=11 to 16, for 150 days, launch oct. 2006
•KEPLER: 100 000 stars, mv=11 to 14 for 4 years, + 70 000 for 1 year, launch end 2008
Limited by data transmission to Earth
A problem for the detection of small planets: background eclipsing binaries
Future missions should:
•Detect more planets
•Diversify the targets
•Detect smaller planets
from SPACE
•Natural but costly
•Limited in telescope size,
number of instruments...
from DOME C
•Promising but uncertain
•Requires precursor mission(s)
Why transit searches at Dome C?
•Continuous night for 3 months
•Excellent weather
Questions:
We don’t know how the following factors will affect transit surveys:
•Sky brightness & fluctuations
•Presence of the moon
•Generally, systematics effect due to the combination of
astrophysical, atmospheric and instrumental noises
Technical problems
•Autonomous operations in cold (-50°C to -80°C) conditions
•Temperature fluctuations
•Icing
•Electrical discharges
A STEP Objectives
1.
Determine the limits of Dome C for precise wide field
photometry (Scintillation and photon noise … or other
noise sources ?)
2.
If the site is competitive with space and transit search
limits are well understood, establish the bases of a midterm massive detection project (large Schmidt telescope
or network of small ones)
3.
Search for transiting exo-planets and characterization of
these planets – Detection of bright stars oscillations.
A STEP: the philosophy behind
•Prepare future photometric projects for
planetary transit detection at Dome C
•Use available equipment, minimize development
work for a fast implementation of the project
•Use experience acquired from the site testing
experiment Concordiastro
•Semi-automated operation
•Directly compare survey efficiency at Dome C
with BEST 2 in Chile for the same target field
Ground based transit projects
Program
Vulcan
Observing site
Mt. H amilton,
California
Status
observing
Telescope Instrument
5,4 cm
Spectral
In struments-560,
Kodak
KAF16800 4k x
4k CCD, Canon
EF300 F/2.8
Hat-1
Kitt Peak, Arizona
under
6,4 cm
construction
Apogee AP 10,
Thomson
THX7899M 2k x
2k, Nikon
180mm f/2.8 MF
ASAS-3
Ź
observing
7,1 cm
Apogee AP 10
2k x 2k , Minolta
200/2.8
STARE
Tenerife, Canary
Islands
observing
10 cm
Pixelvis ion 2 k x
2k CCD, f/ 2.9
BEST
Thueringer
Landessternwarte, observing
Germany
20 cm
CCD AP10
Apogee,
Thomson
THX899M
WASP0
Ź
10 inch
F/2.8 Nikon,
Apogee 10 CCD
camera
(2k x 2k)
Project
La Palma, Canary under
SuperWASP
11,1 cm
Islands
construction
APT
Siding Spring
Observatory,
Australia
OGLE
Las Campanas
Observatory,
Chile
observing
STELLA
Tenerife, Canary
Islands
under
???
construction
RAPTOR A
observing
Field
Limiting
Stars/FOV Precision
of
magnitude
View
x
x
x
x
x
Canon 200mm
f/1.8, 2k x 2k
thinned EEV
x
produced by
Andor of Belfast
x
13 mag
6000
1%
13 mag
20000
0,01 mag
14 mag
8000
Ź
Ź
25000
Ź
13 mag
30000
< 1%
14 mag
Ź
1%
13 mag
43000
Ź
13 mag
Ź
1%
80 cm
Ź
130 cm
8kMOSAIC CCD
camera (SITe
35' x
Ź
2048 x 2049 thin 35'
chip )
Ź
Ź
CCD42-40ŹNIMO
Ź
2k x 2k
Ź
Ź
Ź
Ź
Fenton Hill,
under
70 cm
Jemez Mounta ins construction
Ź
Apogee AP10,
Thomson 7899M 19,5
CCD 2k x 2k,
12 mag
x
Canon 85mm
19,5
f/1.2
10 transiting planets
discovered up to date
– 4 radial velocities +
photometric follow up
– 5 OGLE
– 1 STARE/TrES
Transits photometry – Any problem ?
A huge difference between the expected number of detections and
reality :
Project
Number of detections
expected per season
Real number of
detections
Simulation considering
« systematic effects »
STARE
OGLE
HATnet
Vulcan
UNSW
14
17.2
11
11
13.6
1
1.2
0
0
0
0.9
1.1
0.2
0.6
0.01
DUTY CYCLE
These numbers really depend of the
duty cycle of each campaign
Red Noise
These red noises, or «systematic
effects » are all the noises undergoing
temporal correlations and that we can
not subtract easily.
Systematic effects (F.Pont 2005)
•We only have a partial knowledge of these
effects
•They seem to all result from interaction
between environmental effects with
instrumental characteristics (Pont 2005)
•They are closely linked to the spatial
sampling quality
•For OGLE, the principal source is
differential refraction linked to air mass
changes. (Zucker 2005)
— magnitude dependence with white noise
— magnitude dependence with red noise
Continuous observations
A good phase coverage is
determinant to detect the
large majority of transits
from ground
With a “classical” survey, only
the “stroboscopic” planets are
detectable !
OGLE: transits discovered
•really short periods P ~ 1 day
(rare !)
•stroboscopic periods
Hot Jupiters: periods around
3 days, depth ~1%
Probability of detection of a transit
for a survey of 60 days
With OGLE
For the same telescope with a
permanent phase coverage
Observing at dome C – Lessons from first
two winter campaigns (1)
An exceptional coverage …
 Confirmation by the first winter campaign of the exceptional phase
coverage (cloud coverage, austral auroras)
« First Whole atmosphere night seeing measurements at Dome C, Antarctica »
Agabi, Aristidi, Azouit, Fossat, Martin, Sadibekova, Vernin, Ziad
 Environmental systematic effects considerably reduced:
• air mass
• timescale of environmental parameters evolution
Expectations for future transits search programs
• low scintillation
Observing at dome C – Lessons from first two
winter campaigns (2)
… But a lot of technical difficulties to take
into account
 Frost – different
Behaviour for different
telescopes
Differential dilatations
inside the telescope
Telescope mounts
missfunctionning at
really low temperature
Observatoire de la Côte d'Azur (Laboratoires Cassiopée et Gemini):
THE
A STEP
TEAM
Tristan Guillot
(PI)
Scientific preparation, operation supervision, preparation of
modelling tools, analysis of the results and scientific interpretation
Francois Fressin (IS)
Scientific and technical preparation, modelling tools, analysis of
the results and scientific interpretation
Alain Blazit
Responsible of the camera team; Developpement of test and
acquisition tools.
Jean Gay
Follow-up of the telescope conception; Technical preparation,
optical properties modelling
Yves Rabbia
Telescope environment, follow-up of the telescope conception
Jean-Pierre Rivet
Telescope environment, flat fielding system
Dominique Albanese
Camera control softwares & camera testing expertise
Laboratoire Universitaire d'Astrophysique de Nice:
François-Xavier Schmider
Scientific and technical preparation (telescope), Dome C logistics,
analysis of the results and scientific interpretation
Karim Agabi (PM)
Technical preparation, Dome C logistics, telescope design and
telescope control systems
Jean-Batiste Daban
Technical preparation, Dome C logistics, telescope design and
telescope control systems
Dome C logistics, analysis of the results and scientific
A STEP Telescope
A STEP Characteristics:
CCD DW 436 (Andor)
Size 2048 x 2048
Pixel size 13.5 mm
1.74 arcsec on sky
Camera use:
Defocused PSF
PSF sampling: FWHM covering ~4 pixel
Time exposure: 10s
Readout time: 10s
Telescope mount:
German Equatorial Astrophysics 1200
With controlled heating
Pointing precision tolerated ~.5”
Contractor:
Optique et Vision
ERI
A STEP Camera : Andor DW436
-2048x2048 pixel
-Backwards illuminated CCD
-Limited intra-pixel fluctuations
(Karoff 2001)
-Excellent quantum efficiency in red
-USB2 with antarctisable connection
A precise photometric telescope at Dome C
Telescope tube:
INVAR structure
With Carbon fiber coverage
4Mpixel DW436 CCD
Wynne Corrector
Thermal enclosure for
focal instrumentation
Mode of operation
•
•
•
•
•
One field followed continuously (first year)
Flatfields from illuminated white screens
Data storage: ~500 GB /campaign
Data retrieval at the beginning of Antarctic Summer
Redundancy:
-Two computers in an “igloo” next to the telescope
-Two miror PCs in the Concordia Command Center
(fiber link)
-Two backup PCs
•Semi-automatical:
-Simple control and maintenance every 48 hours
Target stellar field for first campaign
Data processing
Re-use of the major part of BEST
(Berlin Exoplanet Search Telescope)
data pipeline (Erikson, Rauer)
Schedule of A STEP
•PNP, CSA: 64 k€ (approved)
•ANR: 208 k€ (pending)
Schedule of A STEP
CoRoTlux
Stellar field generation
with astrophysical noise sources
Light curves generation
and transit search algorithms coupling
Blends simulation
Using CoRoTlux simulator (end to end
stellar field to light curves generator)
Guillot, Fressin, Pont, Marmier, …
Transit Depth
Expected results …
Simulation done with CoRoTlux
considering 4 stellar fields (1 first
year, 3 second year)
Average of 12 Giant Planets for 10
Monte-Carlo draws
Transit Depth
Considering only planets Giant
Planets (Hot Saturn and Jupiter)
11
12
13
14
15
16
Stellar Magnitude
Exemples of results of two
CoRoTlux simulations
17
False Transit
Discrimination
Many events mimic transits … !
Number of events for 1 CoRoT CCD
CoRoTlux (Guillot et al.)
Grazing Eclipsing
Binaries
background
eclipsing binaries
M Dwarfs
target
planets
Triple Systems
background
planets
target
binaries
Blends discrimination
Within lightcurve:
Ground based follow-up:
+Secondary transits
+Detection level
+Exoplanet “diagnostic” or
“minimal radius” Tingley &
Sackett
+Ellipsoidal variability of
close binaries
(Sirko & Paczynski 2003)
+ Photocenter of the
fluctuation
+Radial velocities (provides
confirmation by a different
method AND planet
characterization) – HARPS
-> 70 to 90 % of transit
candidates could be
discriminated within lighturves
(Estimation from CoRoTlux
results – Fressin)
+Precise photometry with
high resolution telescopes and
Adaptive optics for critical
cases
->99+ % false events
discrimination goal
-> confirmation of most transits
with radial velocities … ?
Conclusions
• A STEP
– Is supported by 6 laboratories, French Dome C commission, Exoplanet
group, Planetology National Program
– Would allow to detect in one season as many transits as all other
ground based transit programs in several years.
– Will do the photometric test of Dome C for future transit search
programs …
• CoRoT
- Will discover and characterize most of the short period giant
planets in its fields, thus largely increase our knowledge of exoplanets
- Will provide statistical information on the presence of short
periods smaller planets
- Could provide the first characterization of super-earth planets
Transit research is determinant for exoplanet
characterization
– Planetary formation and solar system models
– A cornerstone for exobiology programs
Global ongoing study:
Simulation of the optimal transit search program
COROTLUX
->Stellar Field
generator – Guillot et al
(astrophysical noise
sources)
Point Spread Function and image
on CCD – (Fressin, Gay)
(instrumental and atmospheric
noises – masks/PSF fitting)
Light curves generator
-> Systematic and
environmental effects
Search of transits in
lightcurves
-> Treatment, transit
search, discrimination
(-> Number of detections)
Why searching for transits?
Only possible way known to measure
an exoplanet radius
Radius
measurement
(photometry)
Mass Measurement
(radial velocities)
Combined with radial velocity
measurements:
 Mass, density,
composition
Capacity to detect small objets
 Jupiter: 1%; Earth: 0.01%
Ground based projects were almost
unable to discover objects like
Hot Jupiter up today –
But there will be great returns as
their detection threshold
increases