Search for very low mass planets
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Search for very low mass planets Michel Mayor STScI Conference May 2005 Geneva Observatory, Switzerland
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 Presentation
Transcript of Search for very low mass planets
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
