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Search for very low mass planets

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

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Search for very low mass planets

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  1. STScI Conference May 2005 Search for very low mass planets Michel Mayor Geneva Observatory, Switzerland

  2. 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

  3. Outline • The quest for radial-velocity precision • Searching for very low-mass planets • Statistical properties of exoplanets: where theory meets observations • Open questions

  4. Models vs. observations Ida & Lin 2004 New HARPS candidates Rocky planets Icy planets Gaseous giant planets

  5. New HARPS Detections O-C < 2 m/s Lovis et al. 2005

  6. Models vs. HARPS detections Ida & Lin 2004

  7. The quest for radial-velocity precision

  8. The quest for radial-velocity precision and very low-mass planets A few milestones

  9. The quest for radial-velocity precision

  10. The quest for radial-velocity precision

  11. 1 m/s The HARPS planet-search program ESO 3.6 – La Silla - Geneva Observatory - Physikalisches Institut, Bern - Haute-Provence Observatory - Service d’Aeronomie, Paris - ESO

  12. Towards 1 m/s: Stability DRV =1 m/s Dl=0.00001 Å 15 nm on CCD 1/1000 pixel DRV =1 m/s DT =0.01 K Dp=0.01 mbar Vacuum operation Temperature control

  13. Cross-correlation spectroscopy with 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 Cross-correlation function with optimal template  CCF (minimum for the best correlation)

  14. Thorium lines

  15. Simultaneous ThAr reference:Perfomances Mayor et al. 2003, The ESO Messenger

  16. Thermal stability Stability during one day: 0.001 K rms Stability during one year: <0.01 K Rupprecht et al., 2004

  17. Limitations of the RV method • Intrinsic stellar limitations • Stellar activity (amplitude  10-50 m/s) • Modeling -> correction of the effect? • (Saar et al., Kuerster et al.) • Diagnostics: photometry, bisector variation, CaII emission • Effect depends on star rotation and color • Sample selection -> biases? • 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

  18. Asteroseismology: all stars are “singing” HARPS commissioning 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

  19. Asteroseismology on alpha cen B with HARPS • 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 α Cen B α Cen B Series of 400 measurements over 8h

  20. Mu Ara: Acoustic modes 8 nights 250 measures/night Photon noise < 20 cm/s Importance of measurement strategy Acoustic mode Beating Expensive!

  21. Mu Ara: The System UCLES@AAT CORALIE@Swiss-1.2m HARPS@ESO-3.6m • Ara: G5V star with 3 planets

  22. Mu Ara c: A rocky (?) planet of 14 M All HARPS measurements: O-C = 0.9 m/s rms Asteroseismology only: O-C = 0.43 m/s rms

  23. A crop of Neptune-mass planets Mu Ara: P=9.5 days m2sini=14 MEarth Santos et al. 2004 Driver: asteroseismology -> many measurements 55Cnc : P=2.6 days m2sini=14 MEarth McArthur et al. 2004 Driver: inner planets characterisation -> many measurements Gl436 : P=2.8 days m2sini=21 MEarth Butler et al. 2004 M dwarf primary -> relatively “large” RV amplitude Expensive in observational time and needs adequate strategy But Theses objects should be very common HD xxxx b: P=15.6 days m2sini=15 MEarth Udry et al. 2005 HARPS GTO Programme

  24. 55 Cnc: a 4-planet system(McArthur et al. 2004) P=14.6 d e=0.02 M2sini=0.84 MJ P=2.8 d e=0.17 M2sini=14 MEarth P=44.3 d e=0.34 M2sini=0.21 MJ P=5360 d e=0.16 M2sini=4 MJ

  25. HD xxxx b: A new Neptune-mass planet

  26. Possible Kepler-COROT detection Orbit: P = 4.2 d e = 0 K = 0.77 m/s Radial velocities Precision = 0.5 m/s N=50 Mpl = 2 MEarth

  27. Short-period transiting planets 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)

  28. Big telluric planets?? Transit + Radial velocities Precise masses and radii Constraints on physics of intérior of the object Constraints for planetary formation processes Rsmall star ~ Rplanet

  29. D-burning limit The secondary mass function f(m2)~f(m2sini) (Jorissen et al. 2001) Tail up to ~20 MJup

  30. The secondary mass function Total 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

  31. 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

  32. Planet period cumulative function RV exoplanets Stellar companions Migration stop - Magnetospheric cavity - Tidal effect - Roche lobe overflow - Evaporation Very Hot Jupiters ?

  33. Mass-period relation of transiting planets Mazeh, Zucker & Pont 2004 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 ? More data needed

  34. 5 MJup 17 MJup Light brown dwarfs - Massive planets! Chauvin et al. 2004 Definition of a planet ?

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