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

Helioseismology asteroseismology

UVES at the VLTUCLES at the AAT

State-of-the-art Ground-based asteroseismologyof solar-type stars

HARPS at ESO 3.6m

Ground-based

In most cases: • Low SNR• Short obs. period

(Fabien Carrier)

(Fabien Carrier)

High signal-to-noiseobservations ofsolar-like oscillations

Mixed mode

Martic et al. 2004: amp = 40 cm/s per mode

= 6-7 ppm per mode

Martic et al. 2004: amp = 40 cm/s per mode

= 6-7 ppm per mode

Brown et al.1991

2 0 3 1 ???

3 1 2 0

Velocities of Cen A with UVES/VLT

Precision: 50-70 cm/s. Cadence 26 seconds!

UVES/VLT2 + UCLES/AAT

35

Butler, Bedding, Kjeldsen et al. 2003, 2004

2 0 3 1

Radial p-mode (radial orders)

α Centauri system

OPAL EOS, OPAL96 opacity, He, Z settling

(Teixeira et al.)

α Centauri A

α Centauri A

α Centauri B

α Centauri B

Models: Challenges

• Input physics

• Properties: rotation, mixing

• Surface frequency offset

• Avoided crossings – sensitivity to finer details in the models

The Surface Offset

O - C

BiSON Model S

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

How do we improve this?

How do we improve this?

• Higher frequency resolution

How do we improve this?

• Higher frequency resolutionSpace missions

How do we improve this?

• Higher frequency resolution• Lower noise

Granulation dominated

Oscillations dominated

How do we improve this?

• Higher frequency resolution• Lower noise

See the Poster on SONG!

CoRoT (CNES)2006

Seismology for a largenumber of stars

CoRoT (CNES)2006

HD 49385HD 49933HD 181420

CoRoT (CNES)2006

HD 49385HD 49933HD 181420

Same problem as in Procyon…. l=0,2 and 1,3 ridges?The F-star problem

HD 181420

Same problem as in Procyon and HD 49933…. l=0,2 and 1,3 ridges?

02,Simple asteroseismology…

Simple asteroseismology…

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

NASA Keplerlaunched in March 2009

HAT-P-7

Days after launch

Q0 Q1

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

1410

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

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