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Asteroseismology of solar-type stars

Asteroseismology of solar-type stars. J ørgen Christensen-Dalsgaard Institut for Fysik og Astronomi, Aarhus Universitet Dansk AsteroSeismologisk Center. Solarlike pulsators. Mode damping. Damping rate: amplitude / exp( h t), with.

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Asteroseismology of solar-type stars

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  1. Asteroseismology of solar-type stars Jørgen Christensen-Dalsgaard Institut for Fysik og Astronomi, Aarhus Universitet Dansk AsteroSeismologisk Center

  2. Solarlike pulsators

  3. Mode damping Damping rate: amplitude / exp(h t), with Perturbation in convective flux and effect of turbulent pressure perturbation d pt appear to yield negative h, i.e., damped modes

  4. Characteristics of solar-like oscillations • Intrinsically damped by the effects of convection • Stochastically excited by the effects of convection • Typically very small amplitudes (20 cm/sec or 5 ppm for main-sequence stars) Found in stars that are not very solar-like

  5. Large frequency separation: Asymptotics of low-degree p modes

  6. Small frequency separations

  7. Echelle diagram Present Sun

  8. 25 years ago:the start of global helioseismology

  9. Now: the start of solar-like asteroseismology a Cen A (Bedding et al. 2004; ApJ 614, 380)

  10. ESO 3.6 m + HARPS + HARPS clone? The observational breakthrough Very stable spectrographs, motivated by search for exo-planets ESO Very Large Telescope UVES spectrograph

  11. The slightly out-of-date situation Bedding & Kjeldsen (2003; Publ. Astron. Soc. Australia 20, 203)

  12. α Centauri A

  13. α Centauri A Observations with UVES on VLT (Butler et al, 2004; ApJ 600, L75)

  14. α Centauri A VLT(UVES) and AAT(UCLES) optimally combined Bedding et al. (2004; ApJ 614, 380)

  15. α Centauri B UVES (VLT) and UCLES (AAT) Kjeldsen et al. (2005; submitted to ApJ)

  16. Classical observables (a) Pourbaix et al. (2002; Astron. Astrophys. 386, 280) (b) Pijpers (2003; Astron. Astrophys. 400, 241) (c) Kervella et al. (2003; Astron. Astrophys. 404 1087)

  17. Fitting the α Cen system Observable quantities for the system Model parameters: Fit using Marquardt method, with centred differences, using an 8-processor Linux cluster, implemented by T. C. Teixeira Choice of oscillation variables, from Bedding et al. fits to Butler et al. observations:

  18. α Centauri system MA: 1.11111 M¯ MB: 0.92828 M¯ X0: 0.71045 Z0: 0.02870 Age: 6.9848 Gyr OPAL EOS, OPAL96 opacity, He, Z settling (Teixeira et al.)

  19. A borderline case Best-fit model Model with convective core

  20. Model problems? α Centauri A

  21. α Centauri B

  22. η Bootis

  23. Observed power spectrum Kjeldsen et al. (1995; AJ 109, 1313)

  24. Pre-Hipparcos Post-Hipparcos 1.66 M¯ 1.6 M¯ Evolutionary state Christensen-Dalsgaard et al. (1995; ApJ 443, L29)

  25. N,  Boo S2 N, Sun S1 Mode trapping

  26. Mixed modes

  27. Echelle diagram ◦: 0 ∆ : 1 □ : 2 ◊ : 3 Di Mauro et al. (2003; Astron. Astrophys. 404, 341)

  28. Semiregular variables

  29. Miras Semiregular variables Semiregular variables AAVSO observations. Mattei et al. (1997; ESA SP-402, 269)

  30. Statistics of stochastically excited oscillators Energy is exponentially distributed. Hence amplitude distribution is Christensen-Dalsgaard et al. (2001; ApJ 562, L141)

  31. AGB RGB Large-scale surveys OGLE-II observations of LMC Kiss & Bedding (2003; MNRAS 343, L79) (Colour indicates J - K)

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