Transcript Corot-7b the first Super Earth with radius measured

C
R
T-7 b ,c
The
first transiting Super-Earth
fully characterized in
Radius & Mass
(CoRoT+Harps)
a « bonus » :
a system of 2 Super-Earths
D. Rouan, A. Léger, J. Schneider, P. Barge, M. Fridlund, B. Samuel,
and all the Corot Exoplanet Science Team
Short period planets: the small component

2006: first Super Earth detected with gravitational lensing
 Beaulieu et al. Nature 06

Recent results from radial velocity point to a very
significant population of Super-Earth: e.g.
 9.3 M Howard et al. 09
 7.5 M Bouchy et al. 09
 1.9 … 15.6 M Mayor et al. 09

Today 32 planet w M < 0.1 MJup
 Size needed !
Bouchy &al 09
 to derive the structure

One major goal of CoRoT
 detect transits of Super-Earth
 performances allow it
 And indeed a first case !
Pathways Towards Habitable Planets- Barcelonia - Sep 09 - D Rouan
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The star CoRoT-7
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
Spectra UVES, HARPS
Parameters :
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G9V star - mV = 11.7
Teff = 5250 K
Distance = 130 pc ± 30
age ≈ 1.2 Gyr

Very active : emission feature in H and K Ca lines, 2% variability !
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Spots clearly seen crossing the disk because of rotation
rotation period = 23 days
Pathways Towards Habitable Planets- Barcelonia - Sep 09 - D Rouan
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The folded light curve
0.033% !
Transits first detected by alarm mode
 153 transits, all ~ seen when superimposed
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Extremely short period : P= 0.8536 days
transit depth : F/F = 0.033%
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A small planet ?
•
The ennemy : the false positive !
produces a signal that mimics a transiting
planet
•
Grazing Eclipsing Binary
•
Eclipsing Binary in a dwarf/giant system
•
Eclipsing Binary or transiting giant planet
in a triple system

FOLLOW-UP IS MANDATORY !
 A big effort of the whole team
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Follow-up : spectroscopy and imaging

UVES and HARPS spectra
 no blend, K0V star  exclude a dwarf/giant binary system
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ON/OFF photometry of neighbours
 NO mag > alarm  exclude BEB at  > 4”
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Adaptive Optics + Angular Differential Image
 No BEB between 0.4” and 4 ”
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IR spectra with CRIRES-VLT:
 No late K or M earlier than M5V

ROSAT all sky survey
 No very close X binary (e.g. similar to YY Gem)
Pathways Towards Habitable Planets- Barcelonia - Sep 09 - D Rouan
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CoRoT colors
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Triple system with a Jupiter transiting
a second star ?
CoRoT Colors : 3 Light Curves
 Blue, Green, Red
 transit is achromatic !
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Eliminate a triple system because
star_2, and thus the transit signal,
would be red
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Follow-up: Radial Velocity with SOPHIE

Velocimetry with SOPHIE
 2 points
 exclude a planet of mass > 21 M with 95% confidence
 NO grazing Jupiter or white dwarf (exluded by timing anyway)
10 M
corot-7b
21 M
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All known cases of false positives practically
eliminated with a high level of confidence
(risk of a background blend = 8 10-4)
The transit should be due to a
Super Earth planet
of radius 1.7 R
on a very close orbit
with a fairly high probability
Léger, Rouan, Schneider et al., A&A, in press & Xarch
Today, « The Plus » : RV with HARPS
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HARPS Velocimetry (Queloz, Bouchy, Moutou, Hatzes et al. A&A
in press)
:
 106 measurements (70h) during 4 months
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Difficulty : strong variablity of corot-7 affects the CCF
 bissector and FWHM correlates with photometry
 activity : CaII S index
 obvious correlation w rotation (23 days)
corot-7c

Scargle analysis
 after filtering of rotation (3 harmonics)
 first peaks : 3.7 days
 substracted : peak at 0.85 days
 Phase of 0.85 d peak agrees w transit
corot-7b
 Clear confirmation of Corot-7b
 And a second planet !
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Follow-up : Radial Velocity with HARPS (2)
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Finally a two Super-Earth solution is found
Corot-7b
4.8 ± 0.8 M
P = 0.853 days
a = 0.017 AU
R = 1.68 ± 0.1 R
Corot-7c
8.4 ± 0.9 M
P = 3.70 days
a = 0.046 AU

First case of a system with 2 Super-Earths, one in transit
Pathways Towards Habitable Planets- Barcelonia - Sep 09 - D Rouan
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Nature of Corot-7b ?

First solid evidence for a rocky planet !
 A lot of exciting physics (Léger et al. in prep). For instance :
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Tidal forces :
 Phase-locked (tsynch< 100 yrs)
 Elongation under tidal forces < 150 km
 Tidal heating efficient if e ≠ 0
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Temperature
 dark side : 50K
 pretty cold !
 geothermal origin
 dayside :1800-2600 K :
 pretty hot !
 no heat redistribution by atmosphere or ground
 Thus… a temperate region of 90 km width (270-370 K)
 life is however not possible : no water !
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Nature of Corot-7b ?

Structure
 First time density of a SE measured
 5.6 g cm-3 (~Earth) ➜ rocky
 likely silicates mantle
 compatible w 20% of water
 should have migrate
 core of Neptune or rocky telluric
 surface : ocean of liquid rock
 up to z = 50°
 refractory oxydes: CaO, Al2O3
 continent or frost H2O, CO2 elsewhere
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Atmosphere
 escape of all volatiles in 0.1 to 1 Gyr
 composition : vaporised silicates
 tenuous : P = 5-0.05 10-5 bar
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Joan Mirò
Two planets pursued by astronomers…
Corot-7b : a planet of mass and
size cousin of Earth, around a star
cousin of our Sun : a clear
milestone on the pathway we are
exploring at this conference
Cabello perseguido por dos planetas (1968)
Hair pursued by two planets
Thanks extended to the whole CoRoT team
and to the HARPS team
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C
R
T-exo-7b
Planet characteristics
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Period: P = 0.8536 d (one year = 20.5 h)
➜ a = 0.017 AU = 2.8 R
A sun of 28 in the sky !
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Planet characteristics
 Rpl / R✷ = 0.020
 Rpl = 1.70 ± XX R
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