Transcript for CoRoT

COROT, COnvection, ROtation
& Transits exoplanétaires
The CoRoT mission and Brown Dwarfs
Malcolm Fridlund
COROT:
S/C 4.2m x 1.9m x 9.6m, 650kg, 530w
Payload
 CoRoTel, afocal, 27cm aperture, Baffle
 CoRoTcam, dioptric, 4 CCD frame transfer 2048 x 4096
CoRoTcase, electronics box
 Short observing runs (20d -- 60 days) on asteroseismology fields
 Up to 150 days on exo-fields
Objectives
COROT has two design objectives:
- Searching for planets of a type similar to our own Earth
- Studying the inner parts of stars by measuring the changes in light output caused by acoustical
sound waves travelling through the star.
COROT is essentially a very precise light-meter (photometer). COROT have measured changes in stellar
flux of better than1 part in 1 000 000!
Can discriminate between colors ==> COROT can tell what the cause of variations in stellar flux is:
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
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•
•
•
Light curve analysis: Solve for 5 unknown parameters: M*, R*, a, i and Rp 
M* 1/3 / R* with 4 equations from the light curve and Kepler’s 3:rd law
Rp/R* = (DF)1/2 = ((Fno transit – Ftransit) / Fno transit)1/2
Kepler’s third law, the transit shape and transit duration  a, i, M*  R* 
Rp
Under the following assumptions:
–
–
–
–
–
Planet orbit is circular (tend to be true for CoRoT objects)
Mp << M*
Stellar mass-radius relation is known (hmmm)
No ‘blends’
Planet has to enter fully the stellar disk (flat bottom LC) and a good period can be
determined from the LC (long enough non-interupted lc which is the point with
CoRoT).
e.g. Seager & Mallen-Ornelas, Ap.J., 585, 1038, 2003
Launched
27 Dec
2006;
Operated
since 15
Feb, 2007;
About
80000 light
curves
acquired;
Status – First we observed UFO’s
Both US ex-rockets
and Chinese exsatellites….
Now, forget
asteroseismology….
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
Close-in giant objects can be discovered in „alarm mode“
• Very high S/N of data
• transit events visible at N1 level
For example:
CoRoT-Exo-4b
„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 MsunFolie 13
Small stuff is
harder!
Raw light curve!
Cleaned and
normalised 
Lightcurve of 144d,
demonstrating a
rotation period of 2223d
Extracted light curves in color (top) and white light
(bottom)
Lightcurve implies a planet but it can be a background
object or a grazing occultation of a binary: Solved by
photometry and spectroscopy
Photometry from the ground!
PSF of 7b
Spectroscopy of two kinds: Radial Velocities and
high s/n, resolution spectrum for stellar parameters
Teff
Log g
[M/H]
Vmic
V sin i
Results so far
About 20 planets/BD’s (2)
‚not many‘ Earth masses – 47 Jupiter masses
Periods between 0.85 and 96 days
High eccentricity in one case
5 more high probability targets
+ About 80 candidates – many to faint for HARPS/ VLT
Number 3!
CoRoT-Exo-3b
Looked ‘Jupiter-like’
0.43% depth
Light curve analysis: Solve for 5 unknown
parameters: M*, R*, a, I and Rp  M* 1/3 / R*
Transit on target!
High mass!
CoRoT-Exo-3b:
P: 4.2568 d
r: 1.01 RJ (0.07)
m: 21.66 MJ (1.0)
r: 26.4 g cm-3 (5.6)
log g: 4.72 (0.07)
The star:
F3V
V = 13.3 mag
Teff = 6740K
V sin i = 17 km s-1
d = 680pc
1.37±0.09 Mo (lc+models)
R* = 1.56±0.09 RO (lc+models)
Age = 1.6 – 2.8 Gyr
Log g = 4.24±0.07 (models+spectra)
[M/H] = -0.02±0.06
Deleuil et al, 2008, A&A,
491, 889
Transiting planets p < 10d
Radius of 3b is 1 RJ just like theory says!
New BD, P ~ 16d, M ~ 47 MJ F-star
~ 10% (2 out of 20) of planets picked up by
CoRoT are BD
< 5% of all exo-planets are BD (> 13 MJ)
For transiting planets: 5 most massive planets
(our 2 + HAT-P-2b, WASP-14b and XO3b)
orbit all around F-stars
Object
Spect.
P (days)
Mp (MJup)
[M/H]
WASP-14b F5V
2.24
7.7
0±0.2
HAT-P-2
F8
5.63
9.09
0.14±0.08
WASP-18b F9
0.94
10.3
0±0.09
XO-3b
F5V
3.19
11.8
0.17±0.08
CoRoT-3b
F3V
4.26
21.66±1.0 0.02±0.06
CoRoT-?
F
15.9
~ 47
?
What now?
- CoRoT continues – probably for another 3
years but with half the FOV.
- KEPLER has produced its first results.
Demonstrates that they can detect 1 Earth
radii. With this sensitivity, and their RV
program they are going to pick up ~ same
number of BD’s as CoRoT
The End
Public data: http://idoc-corot.ias.u-psud.fr/
Summary:
1. CoRoT have fulfilled design goals by
discovering 7b
2. So far ~10 confirmed planets published
or very close
3. Activity of stars is a surprise. Many
objects turn out metal poor
4. Sun is not a ’normal, average’ star?
5. Amount of follow-up observations
underestimated
– take significant effort and time. HARPS
currently only instrument in the world that can
detect Earth mass planets in RV
6. Will we find Earth-size planets soon? Yes!
- CoRoT, Kepler, microlensing, etc
7. Will we be able to confirm them soon? No!
- not around solar analogue stars except in
exceptional cases (non-HZ orbits)
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