Transits from Space: 1. The CoRoT mission

Transits from Space:
1. The CoRoT mission
Why do Transit searches from Space?
1. No scintillation noise → One can reach the
photon limit
2. No atmospheric extinction → Less false positives
3. Continous temporal coverage → if a stars shows
a transit you will find it!
In short: the light curves are of better quality, have
better temporal coverage so you can find smaller transits
and transits in long period orbits
Disadvantages of Space
1. If the launch fails you do not get a second chance
2. If your instrument breaks, you cannot fix it
3. Space environment introduces different problems
in the light curve analysis
4. It is expensive!
The CoRoT Mission (CNES)
COnvection ROtation and Planetary Transits
• Goals: exoplanets + astroseismology
• Polar Earth orbit
• 27 cm Telescope w/ 4 CCD detectors
• 2.8° x 2.8° field-of-view
• Max 150 days observing runs
• Launched: 27th December 2006
• Participation from: F, A, B, D, E, ESA, Brasil
• Duration 6+ years
CoRoT was successfully launched from Baikanur on
27 December 2006
630 kg +
1000 kg
The Launch Profile of CoRoT:
if (WWIII) then
White House., U.S.A
else if (corot) then
end if
Washington, D.C.
The Orbit of CoRoT
• a = 7278.475 km
• e = 0.00169
• i = 89.984
→ The orbit is nearly perfect
a = 7278.189 km
e = 0.00162
i = 90.002
Porb = 6176–6195 s
The eyes of CoRoT
Movie time!
CoRoT-Mission: Focal Plane
Focal Plane:
Seismo field:
~10 targets/CCD 5 < V < 9.5
Exofield field:
~ 6000 targets/CCD 11 < V < 16
PSF: Astroseismology
2.8o x 1.4o
secondary target
* *
main target
faint stars (11-16)
targets / CCD
PSF: exo-Planet
Field of view
Exofield Information
• CoRoT does not download the entire CCD images, but only the
data in an aperture centered on the star
• 32 sec integrations. On-board summing of data in aperture plus
binning to 512 s exposure time. On-board processing returns only
integrated flux in aperture.
• 400 „oversampled“ apertures with 32 s sampling. This can be
changed during the run
• ~ 40 imagettes. Data from the full image inside the aperture is
sent back
• Chromatic information (CoRoT r,g,b) for only about ½ of the
brightest stars (chromatic and monochromatic light curves)
• ~6000 apertures per exo-CCD. If more stars are in the field one
has to decide before which stars to observed (proposals)
Duty Cycle: Not completely continuous coverage
The South Atlantic
Anomaly (SAA)
• ~ 6% of the data is lost
due to the SAA
• other „random events“
cause 1-2% loss
• Duty cycle ~ 92%
Sample Light Curves from the Exofield
Showing Stellar Variability
So is all this effort worth going to Space?
transit discovery
A CoRoT transit
The CoRoT Ground-based Follow-up Effort
CoRoT only finds transit „candidates“. An extensive
ground-based effort is required to confirm that this is
indeed a planet.
For Space-based transit searches, Ground-based
observations are „part of the Mission“
But before the ground-based follow up starts one needs to do
the best possible analysis on the light curve to give the best
candidates. Much information comes from the light curves
Is the transit too long : probably a giant
Do you see a secondary? Probably an eclipsing binary
Problem : The size of the CoRoT aperture
The CoRoT PSF can have up
to 0-20 background stars
whose light contaminates the
light of the primary star. The
first step is to identify which
star is making the transit
We will go through the necessary
procedures to confirm the planet
for the case of CoRoT-7b!
Status of CoRoT
• CoRoT has been operating for over 4 years
• Over 110,000 stars have been observed
• 24 Transiting Planets have been discovered
• CoRoT mission has been extended for 3 years until
the end of 2013
• On 7 March 2009 CoRoT lost DPU1 (Data Processing
Unit) that controlled one Exoplanet and one Seismo
CCD. CoRoT continues to work well, but only getting
data on ½ the original number of stars
On 6 March 2009 NASA Launched Kepler
The first six CoRoT planets:
P: 1.5089557 days
R: 1.49 RJ
m: 1.03 MJ
r: 0.38 cgs
Barge et al. 2008
P: 9.20205 days
R: 1.19 RJ
m: 0.72 MJ
r: 0.5 cgs
P: 1.742996 days
R: 1.465 RJ
m: 3.31 MJ
r: 1.3 cgs
Alonso et al. 2008
P: 4.0384 days
R: 1.28 RJ
m: 0.459 MJ
r: 0.22 cgs
P: 4.2568 days
R: 1.01 RJ
m: 21.66 MJ
r: 26.4 cgs
Deleuil et al. 2008
P: 8.88 days
R: 1.15 RJ
m: 3.3 MJ
r: 2.3 cgs
Rauer et al., A&A 2009
Fridlund et al., A&A 2009
Agrain et al. and Moutou et al. 2008
And the next 6
P: 0.85 days
R: 0.14 RJ
m: 0.02 MJ
r: 10.1 cgs
Barge et al. 2008
P: 13.2 days
R: 0.97 RJ
m: 2.75 MJ
r:3.7 cgs
Bonnono et al. 2010
P: 6.2 days
R: 0.57 RJ
m: 0.22 MJ
r : 1.6 cgs
Borde et al. 2010
P: 3.0 days
R: 1.43 RJ
m: 2.33 MJ
r:1.0 cgs
Gandolfi et al. 2010
P: 95 days
R: 1.05 RJ
m: 0.84 MJ
r: 0.9 cgs
Deleuil et al. 2008
P: 2.8 days
R: 1.44 RJ
m: 0.91 MJ
r:0.8 cgs
Gillon et al. 2010
P: 4.0 days
R:0.88 RJ
m: 1.31 MJ
r: 2.3 cgs
Cabrera et al. 2011
P: 1.5 days
R: 1.1 RJ
m: 7.6 MJ
r : 7.3 cgs
Tingley et al. 2011
In preparation: CoRoT-16b – 24b
P: 3.1 days
R: 1.12 RJ
m: 63 MJ
r: 59 cgs
Bouchy et al. 2011
CoRoT-1b and its Rossiter-McLaughlin effect
RM anomaly
CoRoT-2b : A Hot Jupiter around an active star
P: 1.742996 days
R: 1.465 RJ
m: 3.31 MJ
r: 1.3 cgs
Alonso et al. 2008
CoRoT-3b : The First Transiting Brown Dwarf
P: 4.2568 days
R: 1.01 RJ
m: 21.66 MJ
r: 26.4 cgs
Pressure support
provided by electron
degeneracy pressure,
no fusion (M < 13 MJup)
Hydrogen fusing
in hydrostatic
(M > 80 MJup)
Brown Dwarfs
Pressure support
provided by electron
degeneracy pressure,
short period of
deuterium burning (13
< M < 80 MJup)
CoRoT-3b : Radius = Jupiter, Mass = 21.6 Jupiter
CoRoT-1b : Radius = 1.5 Jupiter, Mass = 1 Jupiter
OGLE-TR-133b: Radius = 1.33 Jupiter, Mass = 85 Jupiter
Modified From H. Rauer
CoRoT-9b, the first well-known temperate exoplanet
- R = 1.05 RJ
- P = 95.274 d
- a = 0.407 AU
- e = 0.11
- m = 0.84 MJ
- Density = 0.9 gm cm–3
- Teff = 250 – 400 K
Deeg et al., Nature 2010
- longest period planet detected by transits (at time of announcement)
- moderate temperate gas giant
- low eccentricity, thus moderate temparature variations along orbit
CoRoT-7b : The Crown Jewel of CoRoT
In spite of rotational modulation due to spots with a photometric amplitude of
~2% one can find…
CoRoT-7b : The Crown Jewel of CoRoT
Transit Curve
CoRoT-7b: - Rpl = 1.6 R
- P = 0.8536 d
- a = 0.017 AU
- m = 7.4 MEarth
Leger et al., 2009; Queloz et
al. 2009, Hatzes et al. 2010
The „Sherlock Holmes Proof“
Or why we knew CoRoT-7b was a planet before we had
radial velocity measurements.
Hypothesis #1: The transit is
caused by a contaminant
On-off photometry established
that nearby stars could not
account for transit depth of
Hypothesis #2: The star is really a giant star
No, it is a G8 Main Sequence Star
Hypothesis #3: There is a faint very nearby
background eclipsing binary star that causes
the eclipse
Adaptive Optics Imaging shows no very close
Hypothesis #4: A Hiearchical Triple system with 2
eclipsing M-dwarfs,
Short period M dwarfs are very active and we would have seen Ca II
emission from the binary stars and X-ray emission
Hypothesis #5:The transit is caused by a background (or
binary companion) M dwarf with a transiting Hot Jupiter
1. Giant planets to M dwarfs are rare
2 The M dwarf is bright in the Infrared. High resolution infrared spectral
observations show no evidence for an M dwarf companion.
There are only two astronomical bodies that have
a radius ~ 1 REarth:
1. White Dwarf
2. A terrestrial planet
White Dwarfs have a mass of
~ 1 Solar Mass, so the radial
velocity amplitude should be
~ 100s km/s. This is excluded
by low precision radial
velocity measurements.
„Once you eliminate the impossible, whatever remains, no
matter how improbable, must be the truth.”
- Sherlock Holmes
RV (m/s)
CoRoT-7 is an active star with an RV jitter twice that the expected RV
planet from the star
Prot = 23 d
sO–C = 1.7 m/s
sRV = 1.8 m/s
P = 0.85 d
Mass = 7.3 MEarth
A carefull analysis shows that you can extract the planet signal from the
activity signal
Tsurface ~ 1800 – 2600 C
A lava ocean planet?
Art predicting reality?
There is a popular German SF-series
where a Lava planet - called Daa’mur
– populated by exotic life forms which
evolved from thermophile. Therefore
its funny that the first transiting rocky
planet (CoRoT-7b) fits in such a Lavaplanet category.
The CoRoT-7 Planetary System
P = 3.7 Days
Mass = 12.4 ME
P = 9 Days
Mass = 16.7 ME
The analysis of the radial velocity measurements reveals the
presence of 2 additional planets. So why do these not transit?
Only CoRoT-7b Transits
From Diana Valencia
Radius (REarth)