Asteroseismology of solartype stars Revolutionizing the study of

Asteroseismology of solar-type stars Revolutionizing the study of solar-type stars Hans Kjeldsen, Aarhus University

Asteroseismology: Solar-like stars Co. Ro. T HD 49385 1. 2. 3. 4. Measuring oscillation frequencies Identify modes (p, g, mixed, l, n, m) Compute model frequencies Compare observed frequencies with the model The Sun Christensen-Dalsgaard et al. 1995

Observations: Challenges • Accuracy of oscillation frequencies • Mode identification, avoided crossings, (curvature in the Echelle diagram) • Rotational splitting, mode lifetime, mode amplitudes, granulation

Helioseismology asteroseismology

State-of-the-art Ground-based asteroseismology of solar-type stars UCLES at the AAT UVES at the VLT HARPS at ESO 3. 6 m

Ground-based In most cases: • Low SNR • Short obs. period

(Fabien Carrier)

(Fabien Carrier)

High signal-to-noise observations of solar-like oscillations

Mixed mode

Martic et al. 2004: amp = 40 cm/s per mode = 6 -7 ppm per mode

Brown et al. 1991 Martic et al. 2004: amp = 40 cm/s per mode = 6 -7 ppm per mode

2 0 3 4 3 1 ? ? ? 2 0

Velocities of a Cen A with UVES/VLT Precision: 50 -70 cm/s. Cadence 26 seconds!

35 UVES/VLT 2 + UCLES/AAT Butler, Bedding, Kjeldsen et al. 2003, 2004

2 0 3 1

Radial p-mode (radial orders)

α Centauri system OPAL EOS, OPAL 96 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

Bi. SON Model S

The Surface Offset 1. Frequency (f) 2. Large separation MODEL S 3038. 95 135. 855 GOLF 3034. 15 134. 810 radial order, n (21) 0. 16 17 -25 % (21) 0. 78 17 -25 % 3. f(n=17) 4. f(n=13) 2497. 35 1957. 46 2496. 04 1957. 45 0. 05 17 % 13 % 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 resolution Space missions

How do we improve this? • Higher frequency resolution • Lower noise

ted ina m o d n tio ula Gran ted lat l i c s O ion na i m o sd

How do we improve this? • Higher frequency resolution • Lower noise r e t s o e. P h t e Se ! G N O on S

Co. Ro. T (CNES) 2006 Seismology for a large number of stars

Co. Ro. T (CNES) 2006 HD 49385 HD 49933 HD 181420

Co. Ro. T (CNES) 2006 HD 49385 HD 49933 HD 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?

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

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

NASA Kepler launched in March 2009

HAT-P-7

Q 0 Q 1 Days after launch

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

Chaplin et al… 2010 Based on the first half of the KASC Survey… hundreds of stars showing solar-like oscillations

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… • Co. Ro. T, Kepler, PLATO, SONG… will provide the data and challenge theories of stellar evolution • Improved stellar modelling will provide the deeper understanding • Remember to enjoy those amazing data