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

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

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 The slightly out-of-date situation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 )

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 OPAL EOS, OPAL96 opacity, He, Z settling
MA: M¯
MB: M¯
X0:
Z0:
Age: Gyr
OPAL EOS, OPAL96 opacity, He, Z settling
(Teixeira et al.)

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

20. α Centauri A
Model problems?

21. α Centauri B

22. η Bootis

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

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

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

26. Mixed modes

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

28. Semiregular variables

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