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Asteroseismology with A-STEP

Asteroseismology with A-STEP. The sun from the South Pole. Grec, Fossat & Pomerantz, 1980, Nature , 288, 541. Asteroseismology. Angular structure of the modes. n = number of radial nodes  = total number of surface nodes m = number of surface nodes that are lines of longitude

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Asteroseismology with A-STEP

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  1. Asteroseismology with A-STEP

  2. The sun from the South Pole Grec, Fossat & Pomerantz, 1980, Nature, 288, 541

  3. Asteroseismology

  4. Angular structure of the modes • n = number of radial nodes •  = total number of surface nodes • m = number of surface nodes that are lines of longitude •  – m = number of surface nodes that are lines of latitude

  5. Dipole modes l=1, m=0 l=1, m=+1

  6. Quadrupole modes l=2, m=-1 l=2, m=0 l=2, m=-2

  7. g mode (n,) = (10,5) p modes (n,) = (8,100), (8,2) p modes and g modes Gough et al., 1996, Science, 272, 1281

  8. p modes and g modes J. P. Cox, 1980, Theory of Stellar Pulsation, Princeton University Press.

  9. The sun as a star - BiSON

  10. The sun as a star - GOLF large separation small separation

  11. An asteroseismic HR diagram

  12. Bedding, T., et al. 2004, ApJ, 614, 380 Solar-like Oscillations in  Centauri • UVES & UCLES • 42 oscillation frequencies • ℓ = 1-3 • Mode lifetimes only 1-2 days • Noise level = 2 cm s-1!

  13. From G. Houdek Amplitudes in velocity between 10 to 250 cm/s Amplitudes in intensity are of the order of 1-10 ppm

  14. roAp

  15. HR 1217 WET Xcov20 Kurtz et al., 2005, MNRAS, 358, 651

  16. HR 1217 WET Xcov20 Kurtz et al., 2005, MNRAS, 358, 651

  17. p modes:  Cephei stars

  18. HD 129929 = V836 Cen 20-yr multicolour photometry Core overshooting with aOV = 0.1 Non-rigid rotation:4 times faster near core Aerts et al., 2003, Science, 300, 926 Asteroseismology of HD129929: Core overshooting and nonrigid rotation

  19. p modes: EC 14026 stars - sdBV

  20. PG 1336 + 018

  21. g Dor – mixed-mode pulsators

  22. HD 49434

  23. White dwarfs – g-mode pulsators

  24. BPM 37093

  25. A giant solar-like oscillator http://www.lcse.umn.edu/

  26. COROT Field of view • Adaptation of COROTLUX software for variables • Input sample: Besançon model ~ 25000 stars

  27. Pulsation in EXO FoV b Cep: 2 SPB: 29 d Sct: 2500 g Dor: 3200 Hyb : 2200 Ceph: 1 LP: 46 Fraction of variables: 30%?

  28. Stellar limitation • Photon noise < 10-4 up to M=15 • Stellar noise low frequencies • Activity see S. Aigrain • Instrumental limitation • Read-out noise Lower than photon noise for M<16 • Thermal noise negligible • Guiding noise PRNU~1%, • Cosmic rays TBE • Gain variation no data. Global/pixel • Shutter noise 1- 2 ms -> Ti > 30 s

  29. Atmospheric limitations of photometric observations • Transparency fluctuations • Interruptions (clouds) • Scintillation • Diffused light No dust, low humidity, snow < 15 % Better than anywhere else, but still limiting Few auroras, moon These values are still uncertain: A-STEP will contribute to the site qualification

  30. A few words about atmospheric turbulence and scintillation From Dravins et al, 1997

  31. GSM h=3.5m sopd h > 0 m 3 l L0 = 10 m h > 30 m 1 l Interferometric coherence times t0= 0.31 r0/ v ~7 ms T0= 0.31 L0/ v ~775 ms Optical/interferometric parameters Integrated from h=8m Integrated from h =30m s

  32. GSM h=3.5m sopd h > 0 m 3 l L0 = 10 m h > 30 m 1 l Interferometric coherence times t0= 0.31 r0/ v ~7 ms T0= 0.31 L0/ v ~775 ms Optical/interferometric parameters Integrated from h=8m Integrated from h =30m s

  33. Conclusion • Asteroseismology benefits a lot from continuity • A-STEP very similar to COROT EXO Field • Unlike COROT, the full dataset can be recovered • roAp, gDor are top-priority programs • PMS dScuti, Red Giants to be investigated • Solar-type stars ?

  34. Requirements • 30 – 60 s integration time • 90 days continuous observations • Good guiding • Precise timing • Best telescope height still unknown • Color photometry allow mode identification

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