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AFS Lecture 4
COROT, COnvection, ROtation
& Transits exoplanétaires
Objectives
COROT had two objectives:
- Searching for planets of the a type similar to our own Earth (so far unknown around other stars
- Studying the inner parts of stars (for the first time) by measuring the changes in light output caused
by acoustical sound waves travelling through the star.
COROT was essentially a very precise light-meter (photometer). COROT could measure changes in
stellar flux of better than 1 part in 100 000! (For brightest objects a few ppm)
It could discriminate between colours ==> COROT could tell what the cause of variations in stellar flux
were. Either:
a) Intrinsic changes caused by activity or by waves travelling through the star
b) Occultations by a (small) planetary body passing in front of the star
Close-in planetary objects could be discovered in „alarm
mode“
• Very high S/N of data
• transit events visible at N1 level
CoRoT-Exo-4b
CoRoT PSF
How CoRoT planet detection works…
observations
data
reduction
Follow-up
transit
candidate
list
observations
basic data
reduction
transit alarm!
Follow-up
 Preliminary
candidate list
observations
Confirmed
planets
(large planets!)
Giant (and even small
ones) planets can be
detected already in „alarm
mode“!
Confirmed
planets
Follow-up to transits is ground based
• In CoRoT it is complex and comprehensive
• Consists of spectroscopy (high resolution, high
s/n) for
– Stellar modelling (Teff, log g, [Fe/H], v sin i*, Vmic,
Vmac
– Radial velocity determination  Planetary mass *
v sin i*
– Finding contaminant stars within PSF
How to determine the effective
temperature of a star
• For Solar Type stars there are two methods in
Use:
– By calculating the shape of the Balmer line wings
– By using the equivalent widths of a large number
of Fe I and Fe II lines
Teff CoRoT-2 is 5330K+/-70K (internal error)
Teff CoRoT-2 is 5330K+/-70K (internal error)
Teff CoRoT-6 is 5926K+/-100K (internal error)
Determine the equivalent widths of a large number of Fe I
and Fe II lines
The equivalenth width is the width a line would have if it had
100% absorption and covering the same area as the “real”
line. Area proportional to number of absorbing ions
After Teff we must determine the value of g (or rather log g).
This  The estimates the mass of the star
The „first 4“!
CoRoT-Exo-1b
CoRoT-Exo-2b
CoRoT-Exo-2b:
P: 1.742996 d
r: 1.465 RJ
m: 3.31 MJ
The star:
K0V
V=12.6 mag
CoRoT-Exo-1b:
P: 1.5089557 d
r: 1.49 RJ
m: 1.03 MJ
The star:
G0V
V = 13.6 mag
Barge et al. 2008
CoRoT-Exo-3b
CoRoT-Exo-3b:
P: 4.2568 d
r: 1.01 RJ
m: 21.66 MJ
The star:
G0V
V = 13.3 mag
Alonso et al. 2008
CoRoT-Exo-4b
CoRoT-Exo-4b:
P: 9.20205 d
r: 1.19 RJ
m: 0.72 MJ
The star:
F0V
V=13.7 mag
Deleuil et al. 2008
Agrain et al. and Moutou et al. 2008
The „next two“
CoRoT-Exo-5b
CoRoT-Exo-6b
„Discovery space“ for CoRoT
Transiting planets around
variable stars
• Observations made during the first „long run“
of CoRoT of 152 days duration
• ~369000 flux measurements with 512 s
(1. week) and then 32 s sampling
• The star shows periodic variation over
several days due to surface spots
Alonso et al. 2008
The planet:
Period:
Radius:
Mass:
The star:
Type:
Magnitude:
Mass:
1.742996 days
1.465+/-0.029 RJup
3.31+/-0.16 MJup
G7
V=12.6 mag
0.97+/-0.06 Msun
CoRoT-7b
First terrestrial planet found outside solar system…
Raw lightcurve of 144d,
demonstrating a rotation
period of 22-23d
Cleaned and normalised 
No sign of any transit in‘raw‘ light curve
Detection of very small planet signature!
Extracted light curves in color (top) and white light (bottom)
Period 20.2h if a planet the Radius = 1.6 REarth
Lightcurve implies a small planet but it could be a background
object or a grazing occultation of a binary: Solved by photometry
and spectroscopy
Exclude other possibilities
PSF of 7b  Contaminants
Solution to this : On/Off photometry from the ground of potential
contaminants
We need to search for very faint and close by contaminants. For this we use
adaptive optics in the near infra-red.
Workhorses: Photometry, IAC, CFHT,
AO Imaging: NACO, CRIRES
Finally after several months 110 CoRoT-7
radial velocity observations produce a curve
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Small planet
Medium planet
Large planet
The star and its planets
Stellar type: G9V
Stellar mass: 0.91 MSun
Stellar radii: 0.82 RSun
Mass 7b: 8 MEarth
Radii 7b: 1.6 Rearth
P 7b: 20.2h
Mass 7c: ~ 10 MEarth
Radii 7c: Unknown
P7c: 3.4d
Density 7b: 10+/-2 g cm-3
Close-in „small“ objects could even be discovered in
„alarm mode“
The small planet: CoRoT turns out to be the transit
with smallest radius – CoRoT-7b
• First planet under 11 Earth masses with both mass and
radius estimate
• Very likely only one out of 3 planets in this system – a
‚packed‘ system
• Evidence for a ‚rocky‘ world as ´Earth-like‘ as Earth,
Venus and Mercury – at least as far as <r> is concerned
CoRoT-9b
Temperate = 250K-430K
0.84 Mjup
Density = 0.94 g cm-3
Circular orbit, 95d
Distance = 460 pc
G3V
Has been checked for the presence
of a moon – No signs yet!
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CoRoT has today found and published > 35 new planets
The latest to be fully ready for publication is CoRoT-32b – The youngest
planet yet
CoRoT ceased operations due to a technical fault on 2 November 2012 –
two days after having been extended for 3 more years of operations
Between 15 and 30 new planets are expected within the material we already
have – if somebody bothers to carry out the follow-up.
This is going to be difficult since all of the targets are faint
N.B. If we had applied the same criteria as NASA’s Kepler mission we would
already have had a number of more ‘confirmed’ planets
NASA’s Kepler mission – most successful planet finder
March 6, 2009
NASA’s Kepler mission – most successful planet finder
A Kepler light curve is a beautiful thing….
NASA’s Kepler mission – most successful planet finder
Kepler-10 Light Curve
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Period = 45.29 days
Kepler-10 Light Curve
Period = .84 days
Kepler asteroseismology
P-modes in Hat-P-7
Blow-up showing l=0,1,2
Dn0 for l = 0,1,2; filled symbols
is data, open is model 3
Kepler asteroseismology
Kepler result is following:
Planet parameters are now known to < 5% instead of >50%!!!
Stellar Properties
Kepler-10
•
•
•
•
•
54
G4V
Mass = 0.90
Radius = 1.06 R
Age > 8 Gyr
Distance = 560 Light-years
THE END