search for very low mass planets
DESCRIPTION
STScI Conference May 2005. Search for very low mass planets. Michel Mayor. Geneva Observatory, Switzerland. Collaborators Geneva: F. Pepe, D. Queloz, S. Udry F. Pont, D. Ségransan, C. Lovis, A. Eggenberger, X. Bonfils, D. Sosnowska, R. Da Silva - PowerPoint PPT PresentationTRANSCRIPT
Search for very low mass planets
Michel Mayor
STScI Conference
May 2005
Geneva Observatory, Switzerland
Collaborators
Geneva: F. Pepe, D. Queloz, S. Udry F. Pont, D. Ségransan, C. Lovis, A. Eggenberger, X. Bonfils, D. Sosnowska, R. Da Silva
ESO: D. Naef, C. Melo, G. Lo Curto
Grenoble: C. Perrier, J.-L. Beuzit, X. Delfosse
CFHT: T. Forveille
OHP, Marseille: F. Bouchy, J.-P. Sivan, C. Moutou
Bern: W. Benz, C. Mordasini
Lisboa, Aveiro: N. C. Santos, A. Correia
Tel Aviv: S. Zucker, T. Mazeh
CFA: D. Latham
La Laguna: G. Israelian et al.
SA-Verrières: J.-L. Bertaux
The quest for radial-velocity precision
Searching for very low-mass planets
Statistical properties of exoplanets: where theory meets observations
Open questions
Outline
Rocky planets
Icy planets
Gaseous giant planets
Models vs. observationsIda & Lin 2004
New HARPS
candidates
New HARPS Detections
O-C < 2 m/sLovis et al. 2005
Models vs. HARPS detections
Ida & Lin 2004
The quest for radial-velocity precision
The quest for radial-velocity precision and very low-mass
planets
A few milestones
20052005 HD xxxx bHD xxxx b 1515 4.24.2 1.41.4 HARPS/ESO-3.6HARPS/ESO-3.6
The quest for radial-velocity precision
The quest for radial-velocity precision
The HARPS planet-search program ESO 3.6 – La Silla
- Geneva Observatory- Physikalisches Institut, Bern- Haute-Provence Observatory- Service d’Aeronomie, Paris- ESO
1 m/s
Towards 1 m/s: Stability
RV =1 m/s
=0.00001 Å
15 nm on CCD
1/1000 pixel
RV =1 m/s
T =0.01 K
p=0.01 mbar
Vacuum operation Temperature control
Cross-correlation function with optimal template
CCF (minimum for the best correlation)
Cross-correlation spectroscopywith simultaneous thorium monitoring of the spectrograph
drift
- large wavelength domain 3800-6900 A
- high optical resolution R = 115’000
- Very efficient use of the Doppler information
Thorium lines
Simultaneous ThAr reference:Perfomances
Mayor et al. 2003, The ESO Messenger
Rupprecht et al., 2004
Thermal stability
Stability during one day: 0.001 K rms
Stability during one year: <0.01 K
Limitations of the RV method Intrinsic stellar limitations
1. Stellar activity (amplitude 10-50 m/s)Modeling -> correction of the effect? (Saar et al., Kuerster et al.)Diagnostics: photometry, bisector variation, CaII emissionEffect depends on star rotation and colorSample selection -> biases?
2. Binary stars SB2’s -> CCF width-depth anticorrelation Observation dependent light mixing
Time-varying spectral blend-> line shape variations
3. Acoustic modes (asteroseismology)-> Measurement precision and observation strategy
Asteroseismology: all stars are “singing”
acoustic modes visible in various spectral types: e.g. G2 - K1 IV/V
amplitudes up to 10 m/s
periods 4 – 20 minutes
well-resolved with HARPS
Mayor et al. 2003
HARPS commissioning
• stellar pulsations: 40 cm/s rms (individual modes 10-20 cm/s)
• photon noise of individual measurement: 17 cm/s
• sum of all other errors: < 20 cm/s - ThAr method - instrument - guiding - atmosphere
Asteroseismology on alpha cen B with HARPS
α Cen Bα Cen B
Series of 400 measurements over 8h
Mu Ara: Acoustic modes
8 nights250 measures/nightPhoton noise < 20 cm/s
Importance of
measurement strategy
Acoustic mode Beating
Expensive!
Mu Ara c: A rocky (?) planet of 14 M
Asteroseismology only:
O-C = 0.43 m/s rms
All HARPS measurements:
O-C = 0.9 m/s rms
A crop of Neptune-mass planets
Mu Ara: P=9.5 days m2sini=14 MEarth Santos et al. 2004Driver: asteroseismology -> many measurements
55Cnc : P=2.6 days m2sini=14 MEarth McArthur et al. 2004Driver: inner planets characterisation -> many measurements
Gl436 : P=2.8 days m2sini=21 MEarth Butler et al. 2004M dwarf primary -> relatively “large” RV amplitude
Expensive in observational time and needs adequate strategyBut
Theses objects should be very common
HD xxxx b: P=15.6 days m2sini=15 MEarth Udry et al. 2005HARPS GTO Programme
55 Cnc: a 4-planet system (McArthur et al. 2004)
P=14.6 de=0.02M2sini=0.84 MJ
P=44.3 de=0.34M2sini=0.21 MJ
P=5360 de=0.16M2sini=4 MJ
P=2.8 de=0.17M2sini=14 MEarth
HD xxxx b: A new Neptune-mass planet
Possible Kepler-COROT detection
Orbit:P = 4.2 de = 0K = 0.77 m/s
Radial velocitiesPrecision = 0.5 m/s N=50
Mpl = 2 MEarth
5 Mearth 10 Mearth 15 Mearth
F0 (1.60 Msun) 158 40 18
G0 (1.05 Msun) 104 26 14
K0 (0.79 Msun) 78 20 9
M0 (0.51 Msun) 50 13 6
Nb of Doppler measurements (1 m/s) needed to constrain the mass (10% level) of transit detected planets orbiting at 0.1 AU
(HARPS 1 hour for mv = 13 / 2.5 hours for mv = 14)
m/s ]M[
*]UA[
]M[09.0K
sMa
mp
2/
RVK
obsN
Short-period transiting planets
Transit + Radial velocities
Precise masses and radii
Constraints on physics of intérior of the object
Constraints for planetary formation processes
Rsmall star ~ Rplanet
Big telluric planets??
The secondary mass function
f(m2)~f(m2sini)(Jorissen et al. 2001)
Tail up to ~20 MJup
D-burning limit
The secondary mass functionTotal detected
exoplanets:
144
Of which discovered by ThAr technique:
68
(Elodie, Coralie, HARPS, Flames)
Note: m2 sini < 18 MJup
obswww.unige.ch/~naef/who_discovered_that_planet.html
Open Questions• Planets orbiting intermediate-mass stars (m1 ~ 2 – 3 Msun ) evolved stars (Sato, Lovis, Johnson)
• Idem for planets orbiting A-F stars on the main sequence (Galland, Hatzes)
• Planets orbiting metal-poor stars (Latham, Sozzetti, Santos)
• Planets orbiting stars at the bottom of the main sequence m1 < 0.5 Msun
• Tail of the planet-mass distribution from 5 to 20 MJup
• Very low mass planets as a critical test for planet-formation scenarii
• Search for transits of hot-Neptune planets (M-R relation)
• Mass-period relation for short-period planets
RV exoplanets
- Magnetospheric cavity - Tidal effect - Roche lobe overflow- Evaporation
Stellar companions
Planet period cumulative function
Migration stop
?
Very HotJupiters
Mass-period relation of transiting planets
Transiting planets show a well-defined Period-Mass sequence
Evaporation could play a role to remove light close gas giants (Baraffe et al. 2004)
What about heavier hot Jupiters with P>3 days ?
Mazeh, Zucker & Pont 2004
More data needed
Light brown dwarfs - Massive planets!
Definition of a planet ?
17 MJup
5 MJup Chauvin et al. 2004