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Transcript

MHD Days 2014 Dec 3 2014, Potsdam
New results on the ageactivity relation from Kepler
Stellar dynamo from asteroseismology
Alfio Bonanno
INAF Catania Astrophysical observatory
[email protected]
Bonanno, A. Corsaro, E., Karoff, C. A&A 571, 35, 2014
Solar-like Oscillations
n
Acoustic waves in outer convective envelope
(p modes)
⌫n,l,m
Tiny brightness
variations
Observed in > 15000 low
mass stars from MS to Red
Giants
Beck & Kallinger S&W 2013
2
Alfio Bonanno
MHD Days 2014
Solar-like Oscillations
•
•
Chaplin et al. Science 2011
Evidence is a N-dimensional integral
if considered over
the free parameters
⌫max = f (g, Te↵ )
Power Spectral
!
Density = PSD
Amax = f (L, Te↵ )
!
!
Convert evidence
into a one dimensional integral (X =
A2max
fraction of prior volume - i.e. prior mass)
3
Alfio Bonanno
MHD Days 2014
Solar-like Oscillations
p
⌫ / 1/ ⇢¯
•
•
•
•
Chaplin et al. Science 2011
⌫
l=1
dc
⌫/
dr
l=0
l=0
Age, Amax
l=1
l=2
l=2
l=3
⌫max ,
Introduction
The sample
The new method
First results
l=3
⌫
4
Alfio Bonanno
MHD Days 2014
Main goal of asteroseismology
5
Asteroseismic age-activity relation
Sample of 19 MS stars
observed at NOT,
see Karoff et al. 2013
SM W / ⌫
0.25
6
Asteroseismic age-activity relation
SM W / r1.09
BUT THE DATA is
MUCH MORE DISPERSED!
7
Effect of magnetic field on amplitude of oscillation
Numerical simulations (Jacoutot8 et al., 2008)
Alfio Bonanno
MHD Days 2014
Total oscillation power (in quiet Sun units)
Numerical simulations (Jacoutot et al., 2008)
1.0
0.8
0.6
0.4
0.2
0.0
0
200
400
600
800
1000
Initial magnetic field, Bz0, (G)
1200
9
Alfio Bonanno
MHD Days 2014
Activity vs oscillation amplitude
SM W
p
/ 1/ Amax
Amax / 1/B 2
10
CONCLUSIONS
• The activity decreases more efficiently with the
evolutionary status of the star rather then with the age
• The scattering of the LC is not a very good activity
indicator compared to the S-index
• The amplitude of the oscillations are suppressed with
the total magnetic energy released in the atmosphere
• Further data needed to extend these scaling relations
to other stars, but direct numerical simulations can
now be tested along the HR diagram
“Where is your Ekman number?”
Thank you Guenther !