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Time/frequency analysis with COROT: what do we want to do? F. Baudin & E. Michel

Time/frequency analysis with COROT: what do we want to do? F. Baudin & E. Michel. Time/frequency analysis : any method providing an information on the temporal behaviour of the star’s vibrations. For example : wavelet transform, Gabor transform, curvelet analysis, matching pursuit….

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Time/frequency analysis with COROT: what do we want to do? F. Baudin & E. Michel

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  1. Time/frequency analysis with COROT: what do we want to do? F. Baudin & E. Michel Time/frequency analysis : any method providing an information on the temporal behaviour of the star’s vibrations. For example : wavelet transform, Gabor transform, curvelet analysis, matching pursuit… Baudin et al. A&A, 1996

  2. Temporal behaviour of modes = information on the mechanism of excitation of the modes • Several cases: • solar like oscillators : excitation by convection • « classical » pulsators (d Scuti, b Cepheids…) : excitation by k mechanism • Several questions: • are solar like oscillators really solar like? • what is the saturation mechanism in classical pulsators? • other mechanism of excitation? (roAp, SPB, g Dor…) • etc…

  3. Solar like oscillators Do they behave as expected? (the Sun’s case is more or less well understood but it’s only one case) => exploratory program based on the long runs of COROT (150 days of continuous observation is something unique at present time, possibility of statistic studies on power variations and comparison of the different COROT targets) => information on the convection, which can behave in different manners in different stars (thickness of the CZ, efficiency of convection)

  4. Classical pulsators • mechanism increases the amplitude of the modes until « saturation » - What is this mechanism of saturation ? - Is it the same in all classical pulsators ? • Is there evidence of pumping (coupling) of the mode’s power by another mode? • Is there any modulation by the rotation or magnetic activity (or something else) ? • etc… • => Clues for the determination of this unknown saturation mechanism based on the continuous observations of COROT

  5. Other pulsators roAp, SPB, sdB, g Dor: Unknown or not well understood mechanism of excitation => Clues for the determination of this unknown/not well understood mechanism based on the continuous observations of COROT

  6. Solar like oscillators Is there some coupling between modes in solar like oscillators? Modes are independent (orthogonal) in linear approximation, but do we see evidences of coupling and thus the necessity for non linear approach even in the solar like case ? Baudin et al. A&A, 1994

  7. All pulsators Existence of another excitation mechanism? (flare related) Solar case: Ici figure Soho14 Baudin & Finidori, Soho14, 2004 Baudin et al. in prep.

  8. All pulsators Existence of another excitation mechanism? (flare related) GD358 (white dwarf) case: Kepler et al. A&A 2003

  9. How to do that? Wavelet analysis, curvelet analysis, matching pursuit… All have to deal with Heisenberg relation in signal analysis: DT Dn > cte Solar case: l = 0/l = 2 Dn ~ 10mHz => DT ~ 1 day

  10. How to do that? DT ~ 1 day? Presence of noise => spurious power temporal variations DT SNR > cte Need for an estimation of the possible resolution in time and frequency and trade off with noise: Use of simulated data + expected mode spectrum structure

  11. How to do that? (in practice) • Let’s coordinate ourselves! • let’s talk • frederic.baudin @ ias.u-psud.fr / eric.michel @ obspm.fr

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