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

Christensen-Dalsgaard et al Asteroseismology: Solar-like stars 1.Measuring oscillation frequencies 2.Identify modes (p, g, mixed, l, n, m) 3.Compute model frequencies 4.Compare observed frequencies with the model CoRoT HD 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 asteroseismology of solar-type stars HARPS at ESO 3.6m

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

(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

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

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Velocities of  Cen A with UVES/VLT Precision: cm/s. Cadence 26 seconds!

UVES/VLT2 + UCLES/AAT 35 Butler, Bedding, Kjeldsen et al. 2003, 2004

Radial p-mode (radial orders)

α Centauri system OPAL EOS, OPAL96 opacity, He, Z settling (Teixeira et al.)

α Centauri A

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 MODEL SGOLFradial order, n 1. Frequency (f) (21) 2. Large separation (21) 3. f(n=17) f(n=13) % 0.78 % 0.05 % %

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?

Higher frequency resolution

How do we improve this? Higher frequency resolution Space 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 large number of stars

CoRoT (CNES) 2006  HD HD HD

CoRoT (CNES) 2006  HD HD HD

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

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

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

Days after launch Q0Q1

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

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