asteroseismology of solar-type stars revolutionizing the study of solar-type stars hans kjeldsen,...
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Asteroseismologyof solar-type stars
Revolutionizing the study of solar-type stars
Hans Kjeldsen, Aarhus University
Christensen-Dalsgaard et al. 1995
Asteroseismology: Solar-like stars
1. Measuring oscillation frequencies2. Identify modes (p, g, mixed, l, n, m)3. Compute model frequencies4. Compare observed frequencies with
the model
CoRoTHD 49385
The Sun
Observations: Challenges
• Accuracy of oscillation frequencies
• Mode identification, avoided crossings, (curvature in the Echelle diagram)
• Rotational splitting, mode lifetime, mode amplitudes, granulation
UVES at the VLTUCLES at the AAT
State-of-the-art Ground-based asteroseismologyof solar-type stars
HARPS at ESO 3.6m
Models: Challenges
• Input physics
• Properties: rotation, mixing
• Surface frequency offset
• Avoided crossings – sensitivity to finer details in the models
The Surface Offset
n
0
MODEL S GOLF radial order, n1. Frequency (f) 3038.95 3034.15 17-25 (21)2. Large separation 135.855 134.810 17-25 (21)
3. f(n=17) 2497.35 2496.04 174. f(n=13) 1957.46 1957.45 13
0.16 %0.78 %
0.05 %0.0005 %
Observations: Challenges
• Accuracy of oscillation frequencies
• Mode identification, avoided crossings, (curvature in the Echelle diagram)
• Rotational splitting, mode lifetime, mode amplitudes, granulation
Asteroseismology as a tool
• Stellar properties based on the large separation
• 8-10% error in mass, 1% error for the large separation will give a 3% error for the stellar radius
3/20
3/1
0
MR
Asteroseismology as a tool
• Knowledge of the effective temperature (e.g. typical error of 2%) will then give the absolute luminosity (error 10%)
• This will improve the mass and radius estimate further
3/20
3/1
0
MR
Models: Challenges
• Input physics
• Properties: rotation, mixing
• Surface frequency offset
• Avoided crossings – sensitivity to finer details in the models
Kepler Asteroseismic Activities
• Asteroseismology on exoplanet candidates
• Target selection for KASC
• Data distribution via KASOC
• Organizing data analysis
• Workshops; KASC III
• Publishing papers
Based on the first half of the KASC Survey…hundreds of stars showing solar-like oscillations
Chaplin et al… 2010
The challenge…
• Accuracy of oscillation frequencies (Kepler will observe some stars for 3,5 years)
• Mode identification (“F-star problem”)• Rotational splitting, mode lifetime, mode
amplitudes, granulation, activity• Input physics (EOS, opacities, convection,
rotation, mixing) and the surface frequency offset
• Avoided crossings (sensitivity to finer details in the models)
• g-modes