Status of solar and stellar modelling. Jørgen Christensen-Dalsgaard Stellar Astrophysics Centre Aarhus University

Transcription

1 Status of solar and stellar modelling Jørgen Christensen-Dalsgaard Stellar Astrophysics Centre Aarhus University

2 Excellent?

3 Excellent? Probably poor!

4 What kind of models? Model of eclipsing-binary system Stellar atmospheric model Models of convection-zone dynamics Dynamo models of stellar activity Flare models Oscillation background model Models of stellar structure and evolution Models of stellar oscillations

5 SELECTED PROBLEMS Numerical accuracy of model computations Consistency between evolution codes Microphysics (equation of state, opacity, )

6 SELECTED PROBLEMS Numerical accuracy of model computations Consistency between evolution codes Microphysics (equation of state, opacity, ) Stellar hydrodynamics Near-surface convection Convective overshoot Rotational mixing Evolution of rotation Effects of rotation on oscillations

7 SELECTED PROBLEMS Numerical accuracy of model computations Consistency between evolution codes Microphysics (equation of state, opacity, ) Stellar hydrodynamics Near-surface convection Convective overshoot Rotational mixing Evolution of rotation Effects of rotation on oscillations Stellar magneto-hydrodynamics!!

8 A part of the problem Transport processes Mathis (2010; AN 331, 883)

9 Can helio- and asteroseismology help?

10 Can helio- and asteroseismology help? Probably! Kawaler: Harmonious stars can upset the false harmony of our models

11 Relevant data Eclipsing binaries Classical stellar data (log g, T eff, composition, ) Note: very well known for the Sun, including age (although composition??) Surface rotation Surface magnetic field Stellar noise background Oscillation data Frequencies Frequency combinations Excitation Amplitude ratios, phase differences

12 Kawaler

13 Kawaler

14 An old opacity correction Los Alamos Livermore C-D & Petersen (~1992) Also talk by Salmon

15 Another opacity problem? Dziembowski & Pamyatnykh (2008; MNRAS 385, 2061)

16 Approach to diffusive equilibrium in sdb stars Nonadiabatic asteroseismology log HB age (years) 5.25 Stable modes Unstable modes Fontaine et al. (2006; Mem. S. A. It. 77, 49)

17 Unstable modes in sdb star log HB age(years) Stable modes Unstable modes Fontaine et al. (2006; Mem. S. A. It. 77, 49)

18 Relativistic electrons in the Sun No relativistic effects Elliot & Kosovichev (1998; ApJ 500, L199)

19 Relativistic electrons in the Sun Including relativistic effects No relativistic effects Elliot & Kosovichev (1998; ApJ 500, L199)

20 Sun - model Model S: C-D et al. (1996; Science 272, 1286)

21 New surface composition AGS05 AGSS09 Model S C-D & Houdek (2010; ApSS 328, 51)

22 Can opacity corrections solve the problem? AGS05 AGSS09 C-D & Houdek (2010; ApSS 328, 51)

23 Inferred solar internal rotation Near solidbody rotation of interior Base of convection zone Tachocline

24 Stars with solar-like oscillations, from Kepler Chaplin et al. (2011; Science 332, 213)

25 Solar near-twins: 16 Cygni A B Metcalfe et al. (2012; ApJ 748, L10)

26 Required precision Strassmeier: Signal amplitude Signal precision Asteroseismic equivalent: Effect on frequency Frequency error

27 Sharp features in stellar models HeII ionization No overshoot With overshoot

28 Effect of acoustic glitches g Very crudely

29 Fit to acoustic glitches Fit He I He II BCZ Houdek & Gough (2007; MNRAS 375, 861)

30

31 Growing convective cores 2 M X Diffusion No diffusion

32 Diagnostics of a small convective core 1.3 M 0.25 Gyr 5.25 Gyr Cunha & Metcalfe (2007; ApJ 666, 413)

33 Diagnostics of a small convective core 1.3 M Cunha & Metcalfe (2007; ApJ 666,413)

34 g-mode period spacings Miglio et al. (2008; MNRAS 386, 1487)

35 Observed period variations SPB star» 7 M Degroote et al. (2010; Nature 464, 259)

36 Power Into the heart of a giant l = 0 l = 1 l = 2 Fine structure P: core structure Frequency Beck et al. (2012; Nature, 481, 55)

37 Two types of oscillations in one star p-mode behaviour g-mode behaviour

38 Red giants: adiabatic frequencies Montalbán Modes trapped in the envelope (low E) acoustic dominant character Modes trapped in the center (high E) g dominant character Dziembowski et al. 2001; Christensen-Dalsgaard, 2004 Eggenberger et al. 2010; Dupret et al 2010; Mazumdar et al. 2010

39 Montalbán Evolution of a 1.5 Msun

40 Montalbán Evolution of a 1.5 Msun

41 Montalbán Evolution of a 1.5 Msun

42 Montalbán RedG evolution of a 1.5 Msun

43 Montalbán RedG evolution of a 1.5 Msun DP ~ 20-60s

44 Montalbán RedG evolution of a 1.5 Msun DP ~ s

45 Echelle Diagram : RC vs RGB Montalbán M=1.5 Msun l = 2 l = 0 l = 1 l = 2 l = 0 l = 1 RGB RC

46 Period spacing in red giants Montalbán Bedding et al Kepler Core Helium burning phase H-shell burning RGB CoRoT Mosser et al. 2011

47 KIC , an unevolved red giant [Fe/H] = -1 M/M = R/R = 2.62 Age = 12.2 Gyr Deheuvels et al. (2012; ApJ 756, 19)

48 Rotational splitting Deheuvels et al. (2012; ApJ 756, 19)

49 Fitted rotational splittings Solid-body rotation /2¼= 328 nhz Two-zone model Convective envelope, radiative core c /2¼= 696 nhz e /2¼= 51 nhz Deheuvels et al. (2012; ApJ 756, 19)

50 Power Into the heart of a giant Fine structure core structure Frequency Hyperfine structure Core rotation Beck et al. (2012; Nature, 481, 55): Core rotates at least at 10 times the surface rate

51 Fitting individual frequencies Characterize model by set of parameters P = {M, age, Z 0, Y 0, ML, OV, } Compute frequencies Minimize If min(χ 2 ) >> 1 something is wrong with Model: interesting Data errors: a little boring

52 Dealing with large χ 2 : inversion? No adequate model within the given set, specified by the parameters Determine corrections to best-fitting model Identify origin of discrepancies in physical terms

53 Challenges Improve stellar modelling Develop probes that are sensitive to potential problems with the stellar models Location of glitches Frequency region of unstable modes Test the significance of identified problems Provide additional observational data, further to constrain the models

54 Prospects Improved asteroseismic data: more accurate frequencies, modes at lower frequencies, broader range of stars Further extend CoRoT and Kepler BRITE TESS? PlanetVision? PLATO? SONG

55 Prospects Improved asteroseismic data: more accurate frequencies, modes at lower frequencies, broader range of stars Further extend CoRoT and Kepler BRITE TESS? PlanetVision? PLATO? SONG

56 Hail to the chief

57 Hail to the chief