asteroseismology of solar-type stars revolutionizing the study of solar-type stars
DESCRIPTION
Asteroseismology of solar-type stars Revolutionizing the study of solar-type stars Hans Kjeldsen, Aarhus University. Asteroseismology: Solar-like stars. CoRoT HD 49385. Measuring oscillation frequencies Identify modes (p, g, mixed, l, n, m) Compute model frequencies - PowerPoint PPT PresentationTRANSCRIPT
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Asteroseismologyof solar-type stars
Revolutionizing the study of solar-type stars
Hans Kjeldsen, Aarhus University
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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
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Observations: Challenges
• Accuracy of oscillation frequencies
• Mode identification, avoided crossings, (curvature in the Echelle diagram)
• Rotational splitting, mode lifetime, mode amplitudes, granulation
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Helioseismology asteroseismology
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UVES at the VLTUCLES at the AAT
State-of-the-art Ground-based asteroseismologyof solar-type stars
HARPS at ESO 3.6m
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Ground-based
In most cases: • Low SNR• Short obs. period
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(Fabien Carrier)
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(Fabien Carrier)
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High signal-to-noiseobservations ofsolar-like oscillations
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Mixed mode
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Martic et al. 2004: amp = 40 cm/s per mode
= 6-7 ppm per mode
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Martic et al. 2004: amp = 40 cm/s per mode
= 6-7 ppm per mode
Brown et al.1991
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2 0 3 1 ???
3 1 2 0
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Velocities of Cen A with UVES/VLT
Precision: 50-70 cm/s. Cadence 26 seconds!
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UVES/VLT2 + UCLES/AAT
35
Butler, Bedding, Kjeldsen et al. 2003, 2004
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2 0 3 1
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Radial p-mode (radial orders)
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α Centauri system
OPAL EOS, OPAL96 opacity, He, Z settling
(Teixeira et al.)
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α Centauri A
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α Centauri A
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α Centauri B
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α Centauri B
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Models: Challenges
• Input physics
• Properties: rotation, mixing
• Surface frequency offset
• Avoided crossings – sensitivity to finer details in the models
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The Surface Offset
O - C
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BiSON Model S
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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 %
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Observations: Challenges
• Accuracy of oscillation frequencies
• Mode identification, avoided crossings, (curvature in the Echelle diagram)
• Rotational splitting, mode lifetime, mode amplitudes, granulation
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How do we improve this?
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How do we improve this?
• Higher frequency resolution
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How do we improve this?
• Higher frequency resolutionSpace missions
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How do we improve this?
• Higher frequency resolution• Lower noise
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Granulation dominated
Oscillations dominated
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How do we improve this?
• Higher frequency resolution• Lower noise
See the Poster on SONG!
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CoRoT (CNES)2006
Seismology for a largenumber of stars
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CoRoT (CNES)2006
HD 49385HD 49933HD 181420
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CoRoT (CNES)2006
HD 49385HD 49933HD 181420
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Same problem as in Procyon…. l=0,2 and 1,3 ridges?The F-star problem
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HD 181420
Same problem as in Procyon and HD 49933…. l=0,2 and 1,3 ridges?
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Simple asteroseismology…
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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
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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
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NASA Keplerlaunched in March 2009
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HAT-P-7
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Days after launch
Q0 Q1
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Models: Challenges
• Input physics
• Properties: rotation, mixing
• Surface frequency offset
• Avoided crossings – sensitivity to finer details in the models
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Kepler Asteroseismic Activities
• Asteroseismology on exoplanet candidates
• Target selection for KASC
• Data distribution via KASOC
• Organizing data analysis
• Workshops; KASC III
• Publishing papers
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1410
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Based on the first half of the KASC Survey…hundreds of stars showing solar-like oscillations
Chaplin et al… 2010
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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
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The challenge…
• CoRoT, Kepler, PLATO, SONG… will provide the data and challenge the theories of stellar evolution
• Improved stellar modelling will provide the deeper understanding
• Remember to enjoy those amazing data