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Benoît Mosser, for the SIAMOIS team siamois.obspm.fr/

Ground-based Doppler asteroseismology after CoRoT and Kepler. Benoît Mosser, for the SIAMOIS team http://siamois.obspm.fr/. Asteroseismology. What do we need after CoRoT, that Kepler, and hopefully PLATO, will not provide?

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Benoît Mosser, for the SIAMOIS team siamois.obspm.fr/

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  1. Ground-based Doppler asteroseismology after CoRoT and Kepler Benoît Mosser, for the SIAMOIS team http://siamois.obspm.fr/ SIAMOIS

  2. Asteroseismology • What do we need after CoRoT, that Kepler, and hopefully • PLATO, will not provide? • Doppler velocity(Space-borne observations are photometric)Provide additional informationMore precise for structure inversionGround-based • High duty cycle, continuous measurements Dome C in Antarctica provide excellent observation conditions • Scientific objectives require the observation of a few bright targets • for convergence of very precise measurements • observed with a small collector • Asteroseismic program at Dome Csimple, robust, with an easy setup SIAMOIS

  3. Spectrometry / Photometry SIAMOIS

  4. Granulation noise SIAMOIS

  5. HD 49933 CoRoT/HARPS data Mosser et al 2005 Appourchaux et al 2008, in press SIAMOIS

  6. Additional Information Granulation noise at low frequency l =3 modes not visible in photometry SIAMOIS

  7. Large and small separations Small separation Dn1-3 SIAMOIS

  8. Doppler / photometry on the Sun Low low-frequency noise + l=3 modes  Courtesy Thierry Appourchaux Inversion 4 times more precise with Doppler data SIAMOIS

  9. High duty cycle, long duration time series SIAMOIS

  10. Clear sky fraction at Dome C Clear sky fraction (naked eye, Eric Aristidi, 2006 winter) Clear sky fraction > 90% during 84% of the time Average number of consecutive clear days: 6.8 days SIAMOIS

  11. Duty cycle: h_sun = -4° Bad weather Operations: telescope derotation… Sky brightness Mosser & Aristidi 2007 Resulting duty cycle (bright targets) > 90% during 90 days SIAMOIS

  12. Duty cycle: h_sun = -8° SIAMOIS

  13. Duty cycle: h_sun = -13° SIAMOIS

  14. Duty cycle at Dome C [GONG data] Performance at Dome C compared to a 6-site network as GONG (Mosser & Aristidi 2007, PASP) SIAMOIS

  15. Scientific program SIAMOIS

  16. Scientific program • High-precision determination of the interior structure of nearby stars • Age determination ~ a few % • Stellar radii (impact for exoplanet radii) ~ a few % • Composition • Comparative study: photometry / Doppler • Convection, damping, excitation mechanisms • Diagnostic of convective cores; depth of convection and of second Helium ionization zones • Classical pulsators • Non-linear physics, saturation effects, mode coupling • • Stochastically excited modes • Slowly rotating targets • Rotation SIAMOIS

  17. Simulations l = 2 0 3 1 F6V star, mV = 4, vsini = 5 km/s, 90-day long run Modelling: stochastic excitation + intrinsic damping + SIAMOIS characteristics and performance SIAMOIS

  18. 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) SIAMOIS

  19. Targets with a 40-cm telescope Observable solar-like stars with p-mode oscillations for a dedicated 40-cm telescope [for all selected targets SNR > 6 in 5 nights] • 40-cm telescope: • - 7 bright targets, type: F, G, K class: IV & V - many red giants; d Scuti (v sin i < 20 km/s) • Enough targets for completing the scientific program in 3 to 6 winterings SIAMOIS

  20. Targets with a 40-cm telescope Long duration observation  dedicated collector Observable targets (solar-like stars with solar-like oscillations) with SIAMOIS and a 40-cm telescope dedicated to the project SIAMOIS

  21. With a 2-m telescope • dimmer solar-like targets (e.g. star with exoplanets; Sylvie Vauclair’s cancelled talk) • ro Ap + any target with • g doradus vsini < 20 km/s • d scuti mV < 10.5 • red giants • Out of the scope of SIAMOIS: white dwarfs and subdwarf B stars • (too faint magnitude (1319), with a limited number of too broad spectral lines) • Don Kurtz’talk; Gerard Vauclair’s cancelled presentation • For bright targets, dedicated small telescope •  For dimmer targets, shared larger telescope SIAMOIS

  22. Conclusion SIAMOIS

  23. Space / Ground Photometryon faint targets, without any other precise measurements  Statistical approach Precise Doppler measurements on nearby bright targets + convergent measurements (interferometry, high resolution spectrometry…)  Determination of a sample of stellar standards  Insights into the physical laws governing stellar interiors SIAMOIS

  24. Comparison SIAMOIS

  25. Doppler asteroseismology • Space-borne observations = photometric observations • MOST, CoRoT, Kepler, Brite, PLATO… • Ground-based observations = Doppler observations • - less noise at low frequency • - measurement of modes up to degree l= 3 • - observation of bright stars •  very precise inversion and modelling • - looking in great detail into nearby stars • - identifying the physical processes • Dome C = unique site for asteroseismology • 3-month continuous observation with duty cycle ~ 90% • * High performance with a 40-cm collector • * Scientific program with 40-cm and 2-m collectors Next talk http://siamois.obspm.fr Granada:16 - 18/04/ 08 SIAMOIS

  26. Additional material SIAMOIS

  27. 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 SIAMOIS

  28. Fourier Transform Seismometry Fourier transform Seismometry: The Doppler signal is retrieved from the interferogram of the stellar spectrum SIAMOIS

  29. Photometry / activity SIAMOIS

  30. Bright targets Solar-like targets with solar-like oscillations [A scaled to (L/M)0.7] - d Scuti - g Dor - PMS - Red giants SIAMOIS

  31. An example HD 203608, F8V, mV = 4.2 Observations with HARPS: - 5 nights - duty cycle ~ 40 % - SNR = 5 Precision of interior structure parameters improved by a factor 3 to 10 Mosser et al 2008 SIAMOIS

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