View
226
Download
1
Embed Size (px)
Citation preview
Inside a quaking star: asteroseismic analysis of alpha Centauri
Jørgen Christensen-Dalsgaard
Institut for Fysik og Astronomi, Aarhus Universitet
Teresa Teixeira, Timothy R. Bedding, Hans Kjeldsen ,
Frank P. Pijpers
Back to the future:the solar case
Grec et al., Nature 288, 541; 1980
α Centauri A
Observations with UVES on VLT
(Butler et al, 2004; ApJ 600, L75)
Asymptotics of p modes
Frequency separations:
Near-surface frequency effectsStellar structure and oscillation modelling deal inadequately with
• Treatment of convection in modelling (thermal structure, turbulent pressure)
• Mode damping excitation
• Dynamical effects of convection on oscillations
• Atmospheric structure
These effects are concentrated very near the surface
Near-surface effects (II)General frequency differences between star and model can be represented as
Note:
Near-surface effects are contained in H2
Solar data,
l = 0 - 100
Solar data,
l = 0 - 100
Near-surface effects (III)
From solar observations over a range of degrees, H2(¯)() is known.
Can that be used for other stars, somehow?
Use as ansatz
On physical grounds we expect
α Centauri A
α Centauri A
VLT(UVES) and AAT(UCLES)
optimally combined
Bedding et al., ApJ, submitted
Fitting observed frequencies Cen A
α Centauri B
UVES (VLT) and UCLES (AAT)
Kjeldsen et al. (in preparation)
Classical variables
(a) Pourbaix et al. (2002)
(b) Pijpers (2003)
(c) Kervella et al. (2003)
Fitting the α Cen systemObservable quantities for the system
Model parameters:
Fit using Marquardt method, with centred differences, using an 8-processor Linux cluster, implemented by T. C. Teixeira
Choice of oscillation variables, from fits to observations and model frequencies:
α Centauri system
OPAL EOS, OPAL96 opacity, He, Z settling
(Teixeira et al.)
MA: 1.11111 M¯
MB: 0.92828 M¯
X0: 0.71045
Z0: 0.02870
Age: 6.9848 Gyr
α Centauri system
: A: B
α Centauri A
Observations: use Bedding et al. fits
Models: surf = 0.75
α Centauri B
Observations: use Bedding et al. fits
Models: surf = 0.75
α Centauri A
Observations: use Bedding et al. fits
Models: surf = 0.75
α Centauri B
Observations: use Bedding et al. fits
Models: surf = 0.75
What is next?
Better data
Better models
Better analysis techniques
More stars
The future
Rømer: a Danish micro-satellite project
?
A swarm of Rømers