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PLAnetary Transits and Oscillations of stars Thierry Appourchaux for the PLATO Consortium http://www.oact.inaf.it/plato/PPLC/Home.html Outline - Science Objectives - Instrumental Concept - Expected Performances - Conclusion Science Objectives (1/2) • Understand formation and evolution of planetary systems (= planets + host stars) • Understand evolution toward habitability • Complete statistical study of exoplanetary systems • Identification and characterisation of planetary systems - including planets of all masses and sizes on various orbits - around stars of all types and ages - including seismic characterization of planet host stars - in particular rocky planets in habitable zone of solar-like stars Science Objectives (2/2) Goal: detect and characterise exoplanets - measurement of radius and mass, hence of mean density - estimate of age Method: transit search AND seismic analysis on the same stars - photometric transits : Rp/Rs (Rs known thanks to Gaia + seismology) - radial velocity follow-up : Mp/Ms - seismic analysis of host stars : Rs, Ms, age Tool: - ultra-high precision, long, uninterrupted CCD photometric monitoring of very wide samples of bright stars: CoRoT - Kepler heritage Why a seismic analysis of planet host stars? We want to compare exoplanet characteristics to model predictions with various compositions and structures maximum acceptable error bars standard error bar (no seismology) 10% PLATO error bar (with seismology + Gaia) 5% 10% - 5% Wagner et al. 2009, also: Valencia et al. 2007 - seismically determined masses and radii of host stars are required to derive useful constraints on planetary interiors - will give us the opportunity to study diversity of planets : planets with same radius and different masses - seismically determined exoplanetary ages will be used to place exoplanets in an evolutionary context PLATO target samples Main focus of PLATO: Bright and nearby stars !! > 20,000 bright (~ mV≤11) cool dwarfs/subgiants (>F5V&IV): PLATO… is watching you ! exoplanet transits AND seismic analysis of their host stars AND ultra-high precision RV follow-up >1,000 very bright noise < 2.7 10-5 in 1hr for 3 years (mV≤8) cool dwarfs/subgiants for 3 years exoplanets around bright and nearby stars >3,000 very (mV≤8) cool dwarfs/subgiants > 5,000 (3 years) + 5,000 (5 months) nearby M-dwarfs (mV≤15-16) noise < 8. 10-4 in 1hr > 250,000 cool dwarfs/subgiants (~ mV≤13) exoplanet transits + RV follow-up noise < 8.10-5 in 1hr for 3 years bright for >5 months Noise requirements: transit search simulation: 1 R planet transiting a solar-like star at 1 AU - mean of 3 transits transit detectable transit well characterized noise requirement ≤ 2.7 x 10-5 in 1 hr for high S/N transit measurement for transit search : ≤ 8.0 x 10-5 in 1 hr for marginal transit detection Noise requirements: seismic analysis ≤ 2.7 x 10-5 in 1 hr power (ppm2/Hz) CoRoT HD 49385 mV = 7.4 137 days PLATO equivalent mV = 9.6 same data noise 2.7 x 10-5 per hr PLATO equivalent mV = 11.1 oscillation spectrum still distinguishable although affected by noise frequency (Hz) Instrumental Concept Very wide field + large collecting area : multi-instrument approach optics 356 mm 164.6 mm S-FPL51 L-PHL1 N-KzFS11 CaF2 S-FPL53 KzFSN5 (Lithotec) FPA fully dioptric, 6 lenses focal planes optical field 37° 4 CCDs: 45102 18m New design - 32 « normal » cameras : cadence 25 sec - 2 « fast » cameras : cadence 2.5 sec - pupil 120 mm - huge dynamical range: 4 ≤ mV ≤ 16 !! « normal » « normal » FPA « fast » FPA Orbit around L2 Lagrangian point, 6-year nominal lifetime + possible extension Concept of overlapping line of sight 4 groups of 8 cameras with offset lines of sight baseline offset = 0.35 x field diameter (k=0.35) 16 24 16 24 32 24 8 8 16 50° 37° 8 24 16 8 Optimization of number of stars at given noise level AND of number of stars at given magnitude Sky coverage Observation strategy: 1. two long pointings : 3 years + 2 years or 2 years + 2 years 2. « step&stare » phase (1 or 2 years) : N fields 2-5 months each 12 0° Kepler PLATO 15 0° 90 ° 18 0° 60 ° CoRoT CoRoT 21 0° 22 h 20 h 18 h 16 h 14 h 12 h 10 h 8h 30 ° 24 0° 0° 27 0° 33 0° 30 0° >50% of the sky ! PLATO 6h 4h 2h 0h Expected noise level noise calculated for 32 cameras noise in 1 hr (ppm) jitter/confusion + background photon noise dominant photon noise jitter/PRNU Performances of the long pointing phases as a function of noise level PLATO (4360 deg2) Kepler (100 deg2) noise level (ppm/√hr) nb of cool dwarfs & subgiants mV range nb of cool dwarfs & subgiants mV 27 22,000 9.6 - 10.9 1,300 11.2 80 330,000 11.6 - 12.7 spec 250,000 25,000 13.6 8 30 8 11 1,300 11 spec 20,000 1,290 spec 1,000 58,490 maximum noise level for seismic analysis of solar-like stars & earth-like planet transit measurement as a function of magnitude numbers of cool dwarfs and subgiants observable by PLATO and Kepler, for various photometric noise levels and various magnitudes, during long monitoring sequences Note that solar-like oscillations will be measurable for more then 20,000 dwarfs! Scientific Impact Expected number of detected transiting planets by PLATO and Kepler: - each star has one and only one planet in each cell - planet is detected if a transit signal AND a radial velocity signal are measured - intrinsic stellar « noise » is taken into account numbers in white are expected numbers of detections by PLATO and Kepler in each cell: Kepler contributions are represented by the green sectors. Orbit semi-major axis in units of habitable zone The lower right corner (telluric planets in the HZ), not covered by Kepler because of the overwhelming difficulty of FU observations, will be explored by PLATO thanks to its focus on bright stars. Note that all planets detected by PLATO referred to in this diagram will have their host star fully characterized by asteroseismology Conclusion Building on CoRoT and Kepler experience, - PLATO is a next generation planet finder and characterizer - its focus will be mainly on bright and nearby targets - it will detect and characterize significant numbers of telluric planets in the habitable zone - PLATO will provide seismic analysis of planet host stars and of a very large sample of stars of all types and ages - PLATO will represent a major step forward after the pioneering CoRoT and Kepler missions