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SIAMOIS : asteroseismic observations after CoRoT: the need for spectroscopic measurements

SIAMOIS : asteroseismic observations after CoRoT: the need for spectroscopic measurements. Benoit Mosser - LESIA (presented by Jean-Pierre Maillard , IAP). Outline. Asteroseismology Photometric observations with CoRoT Spectroscopic results from ground (HARPS, …)

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SIAMOIS : asteroseismic observations after CoRoT: the need for spectroscopic measurements

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  1. SIAMOIS : asteroseismic observations after CoRoT: the need for spectroscopic measurements Benoit Mosser - LESIA (presented by Jean-Pierre Maillard, IAP) Spectroscopy at Dome C

  2. Outline • Asteroseismology • Photometric observations with CoRoT • Spectroscopic results from ground (HARPS, …) • Performance comparison • Photometric measurements • Doppler measurements • Doppler measurements • Grating spectrometer • Fourier tachometer • 4. SIAMOIS • Principle • Scientific program • Schedule Spectroscopy at Dome C

  3. Asteroseismology purpose • Age determination ~ a few % • Stellar radii (impact for exoplanet radii) ~ a few % • Stellar composition • Diagnostic of convective cores • Depth of convection and of second helium ionization zones • Mode excitation mechanisms (convection) • Rotation and internal structure Specification: eigenfrequency resolution dν = 0.2 μHz continuous observations (h > 80 %) long duration (dν= 1/T) (T > 2.5 months) Spectroscopy at Dome C

  4. CoRoT • launched on December 27th , 2006 • by Soyuz 2, from Baikonour, Kazakhstan • low Earth polar orbit, 896 km altitude • orbital period 6184 s (~1h43mn, 162 mHz) • high precision photometry • The CoRoT space mission was developped and is operated by CNES, with the contribution of Austria, Belgium, Brazil, ESA, Germany and Spain Spectroscopy at Dome C

  5. CoRoT light curves • Typical CoRoT light curve •  Photon noise limited performance ~ 1 ppm • 150 days • Duty cycle ~ 92% Typically 10-4 in 30 s Variability below the 10-3 level over 20 days of a 6th magnitude F star Spectroscopy at Dome C

  6. Photometry (1) HD 49933, mV=5.7, F5V, observed during the initial run (60 days) Mode amplitudes ~ 1 few ppm  observation of p-mode oscillations in solar-like stars not achievable by photometric ground-based measurements Spectroscopy at Dome C

  7. Photometry (2) HD 181420, mV=6.7, F2V, first long run (150 days) Stellar granulation: important contribution at low frequency  limits the spectrum SNR for f < 2 mHz Spectroscopy at Dome C

  8. Ground-based observations • solar-like oscillations in solar-like stars • HARPS @ ESO 3.6-m • UCLES @ AAT • CORALIE @ Euler telescope • SOPHIE @ OHP • + instruments @ SARG, McD, Okoyama, Lick Observations limited to a few days Spectroscopy at Dome C

  9. Spectroscopic result (1) • Procyon, 10-day network observation • (11 observatories, Jan. 2007) • Identification of mixed modes •  Definitely a post-MS star Mosser et al 2008, A&A 478, 197 Bedding et al 2008, in preparation Day aliases (11.57 Hz) still present; too short duration compared to stellar rotation period Spectroscopy at Dome C

  10. Spectroscopic result (2) HD 203608 ; F6V ; mV = 4.8 Old star of the thick galactic disk 5 days observation with HARPS duty cycle 40% Stellar modelling before with asteroseismic constraints L/Lo 1.40 ± 0.13 1.38 ± 0.045 M/Mo 0.88 ± 0.07 0.928 ± 0.028 R/Ro 1.04 ± 0.12 1.06 ± 0.02 T (K) 6070 ±150 6051 ± 45 Fe/H-0.60 ± 0.10 -0.55 ± 0.05 Age (Gyr) 10.5 ± 4 7.2 ± 0.3 Mosser et al 2008, submitted to A&A Precision still hampered by poor frequency resolution and duty cycle Spectroscopy at Dome C

  11. Doppler asteroseismometry • Principle : photon noise limited performances • - Qquality factor of the spectrum • - Ne number of photoelectrons collected • Q depends on: • - the spectral type and the v.sini (rotation) of the star • the type of instrument • GS: grating spectrometer • FS: Fourier Transform spectrometer Spectroscopy at Dome C

  12. Quality factor • The quality factor Q gives • a measure of the: • number • depth • width • of the lines in the stellar spectrum • Q # dln A /dln l • Better Q factor for cooler stars • Better performances in the blue part of the visible spectrum Supposes a high resolving power (~ 100 000) of the grating spectrometer Spectroscopy at Dome C

  13. Comparison: Photometry/Spectrometry Photometry Spectrometry Q = stellar oscillation quality factor Oscillation amplitudes 1 ppm  10 cm/s Photometric observations: dimmer targets, or smaller telescope 1 ppm sensitivity require space-borne observations Spectroscopy at Dome C

  14. Doppler / photometry on the Sun Solar granulation noise: photometric observations 50 times noisier at low frequency than Doppler measurements Spectroscopy at Dome C

  15. Granulation noise Spectroscopy at Dome C

  16. l=3 modes l=3 modes have higher visibility in spectroscopy Small separation Spectroscopy at Dome C

  17. Doppler / photometry on the Sun Core size determination low frequency noise + l=3 modes  Inversion 4 times more precise with Doppler data Gabriel et al 1998 Spectroscopy at Dome C

  18. Space / Ground Spectroscopy at Dome C

  19. Fourier Transform Seismometry Fourier transform Seismometry: The Doppler signal is retrieved from the interferogram of the stellar spectrum Spectroscopy at Dome C

  20. Fourier Transform Seismometry FT seismometry successfully tested with the FTS at CFHT Procyon Mosser et al. 1998, A&A 340, 457 Jupiter Mosser et al. 2000, Icarus 144, 104 • FTS at CFHT: repeated scan of one selected fringe of the interferogram • shift of the fringe signal with time  Doppler signal Spectroscopy at Dome C

  21. FS: quality factor with • (Mosser, Maillard, Bouchy 2003, PASP 115, 990) • Q increases with • wavenumber s0 • working path difference dopt • fringe contrastC • A high fringe contrast C requires a narrow bandwidth • To be compatible with a high Nefactor requires a dispersion of the • fringes (post-disperser) = many adjacent narrow bandwiths Spectroscopy at Dome C

  22. FS: Q with post-dispersion Fourier transform seismometry with post-dispersion The Doppler signal is searched in the interferogram of each spectral element defined by the post-disperser Q factor as a function of the post-dispersion resolution and the spectral type for 3 vsini Spectroscopy at Dome C

  23. GS / FS GS: HARPS (ref = ThAr lamp) R ~ 115000 FS: post-dispersion resolution R~ 1000 δv(GS) / δv(FS) as a function of v sini and T of the star GS > FS if reference = ThAr lamp (Mosser et al. 2003) GS ~ FS if reference = iodine cell Spectroscopy at Dome C

  24. GS / FS FS: smaller and simpler instrument than a GS monolithic interferometer = no moving parts (SIAMOIS concept)  possible installation and setup at Dome C Spectroscopy at Dome C

  25. SIAMOIS = SystèmeInterférentielAMesurer les OscIllationsStellaires • A Fourier Spectrometer dedicated to asteroseismology with no moving parts • to be installed at Dome C behind a 40-cm telescope • phase A completed • P.I. B. Mosser • Scientific Committee • Th. Appourchaux (France, pdt), C. Catala (inst. scientist), S. Charpinet (France), D. Kurz (UK), Ph. Mathias (France), A. Noels (Belgium), E. Poretti (Italy), Spectroscopy at Dome C

  26. SIAMOIS performances at Dome C • Photon noise limited performances • SIAMOIS, at Dome C, 40-cm telescope, • 120 hours with 95% duty cycle, mV = 4 • ‘‘SNR’’ on circumpolar targets Spectroscopy at Dome C

  27. SIAMOIS performances at Dome C SIAMOIS with post-disperser R = 1000 at Dome C for 3 solar-like stars Spectroscopy at Dome C

  28. Targets • K, G, F, class IV & V targets • Red giants • Delta-Scuti, gamma Dor, PMS… Since long-duration observations are required, a 40-cm telescope provides already a scientific program on p-mode oscillation in solar-like targets as large as the CoRoT program Spectroscopy at Dome C

  29. Targets with a 40-cm telescope COROT Observable solar-like stars with p-mode oscillations for a dedicated 40-cm telescope • 40-cm telescope: • - 7 bright targets, type: F, G, K class: IV & V - many red giants; d Scuti (v sin i < 20 km/s) • Scientific program for more than 6 winterings • Program complementary to CoRoT Spectroscopy at Dome C

  30. Clear sky fraction at Dome C Clear sky fraction measured by Eric Aristidi (2006 winter) Clear sky fraction > 90% during 84% of the time Average number of consecutive clear days: 6.8 days Spectroscopy at Dome C

  31. Duty cycle Better performance at Dome C compared to a 6-site network (Mosser & Aristidi 2007, PASP) Spectroscopy at Dome C

  32. SIAMOIS • 40-cm telescope small size, low cost, easy ‘antarctization’, dedicated to the project • Interferometerfiber fed Mach Zehnder interferometer, operated at room temperature, monolithic no moving parts, photon noise limited performance • Dataautomatic pipeline reduction, telemetry: limited flow < 100 kb/day Phase A completed, April 2007 Spectroscopy at Dome C

  33. Simulations l = 2 0 3 1 F6V star, mV = 4.5, vsini = 5 km/s, 90-day long run Modelling: stochastic excitation + intrinsic damping  Lorentzian profiles (Anderson et al 1990) Spectroscopy at Dome C

  34. Simulations Longer lifetimes at low frequency  clear multiplets l = 2 0 3 1 F6V star, mV = 4.5, vsini = 5 km/s, 90-day long run Precision on the eigenfrequency measurement: 0.10 – 0.25 mHz(Libbrecht 1992) Spectroscopy at Dome C

  35. Fourier tachometer • Another advantage: multi-object advantage •  simultaneous observations of several targets First step: small telescope + FT Then: multi-targets observation = small telescopes + 1 FT Spectroscopy at Dome C

  36. Planning & budget • < 2006 • principle: monolithic Fourier • Tachometer • 2007 • thermo-mechanical analysis • phase A • 2009-2011 • PDR • FDR • integration • 2011-2012 • tests • summer campaign: Dome C • 2013 • First winterover at Dome C LESIA (Obs. Paris), IAS (Orsay), LUAN (Nice), OMP (Toulouse) + SESO Budget ~ 860 k€ << budget for an equivalent 6-site network Spectroscopy at Dome C

  37. Perspectives • Asteroseismology requires uninterrupted long-duration time series ! • 1 dedicated 40-cm telescope: • first season observation • fiber FOV = 5’’ (>> seeing) • stellar magnitude < 5 for solar-like oscillations < 7 for classical pulsators 2 or 3 dedicated small telescopes - next step • simultaneous observations of 2 or 3 stars 2-m class telescope? • stellar magnitude < 8.5 for solar-like oscillations • increase of the number of reachable targets • possibility to achieve specific observations in selected targets • However, a dedicated telescope would be required Spectroscopy at Dome C

  38. Other projects: KEPLER • NASA; launch = nov 2008 • High precision photometry • a few fields reserved • for asteroseismology • CoRoT  Kepler : • tel. 27 cm  95 cm • orbit polar  L2 • + duty cycle in L2 • sensitivety (mV > 9), radiations in L2 • ? exact scientific case for asteroseismology? • 29-31 October 2007: First KASC workshop, Paris. The Kepler Asteroseismic Science Consortium (KASC) is an international consortium of researchers dedicated to the asteroseismic analysis of Kepler data. Spectroscopy at Dome C

  39. SONG • Project currently in phase 0 • Danish asteroseismology centre, Aarhus University • Network of 6 to 8 small telescopes (6080 cm) • Echelle spectrometer + iodine cell • Expected schedule: 1 prototype for 2012-2013 >> 2012 Spectroscopy at Dome C

  40. Comparison Spectroscopy at Dome C

  41. Conclusions • Space-borne observations = photometric observations • CoRot unique results • Kepler not primarily specified for asteroseismology • sensitivity for p-mode oscillations under question • very dim targets  uncertainty on fundamental parameters • Ground-based observations = Doppler observations • measurement of modes up to degree l = 3 • much less low frequency noise •  much better inversion and modelling • observation of low mass stars • Network very late schedule, complex organization • Dome C = unique site for asteroseismology • 3-month continuous observation with duty cycle ~ 90% • High performance with a 40-cm collector • Better performance than a 6-site network http://siamois.obspm.fr Spectroscopy at Dome C

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