Solar-like Oscillations in Red Giant Stars
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Solar-like Oscillations in Red Giant Stars Olga Moreira BAG
description
Solar-like Oscillations in Red Giant Stars. Olga Moreira. BAG. Outline:. What is asteroseismology Oscillatory properties of stars Solar-like oscillations Solar-like oscillations in red giant stars. What is asteroseismology?. - PowerPoint PPT Presentation
Transcript of Solar-like Oscillations in Red Giant Stars
Solar-like Oscillations in Red
Giant Stars
Olga Moreira
BAG
Outline:
What is asteroseismology Oscillatory properties of stars Solar-like oscillations Solar-like oscillations in red giant stars
What is asteroseismology?
Definition: It is the study of the internal structure of stars through the interpretation of their oscillation frequencies
Stars are not as quiet as they seem...
Seeing with the sound
P , T,
Can we hear stars?
20 Hz to 20 000 Hz
Bats~50 000 Hz Blue Whales ~10 to 200 Hz Hya~ 60 Hz
How do we describe oscillations in stars?
Radial displacement eigenfunction, =r:
Oscillations modes are described in terms of three quantum munbers: n (order or overtone, number of radial number), l (degree, number of surface nodes), m (azimuthal order, number of surface that are lines in the longitudinal)
Radial modes
l=0 n=0 l=0 n>0
Non Radial modes and Rotation
l=1 m=0 l=2 m=0 l=2 m=2
Rotation:
Multiplets with 2l+1 components separated by (1-Cn,l)
How does asteroseismology work?
Waves propagation in starsfr
eq
uen
cy
Radius
P modes G modes
l
(
Hz)
For n>>l there is an asymptotic relation saying that the modes are equally spaced :
In frequency for p modes :
In period for g modes:
0
Why do stars pulsate?
Driving/Excitation mechanism
The pulsation can only continue if energy is fed into the pulsation via a driving mechanism.
• -mechanism: opacity
• -mechanism: energy generation rate in the stellar core
• Stochastic driving: Convective zone
To see if the star can sustain pulsations one need to evaluate work ontegral, W, which is defined as an increase of the total energy over one period.
Examples of pulsations in stars
Cepheids pulsate in fundamental radial modes but some also pulsate in the first overtone.
Solar-like oscillators and roAp: high-order pmodes
White dwarfs: high-order g-modes
Why? What selects the modes of pulsations in stars?
Heliosesimology
Taunenbaum & Howard (1969)
Deubner (1975)
http://solar-center.stanford.edu/images/lu2-sm.gif
Where did Helioseismology led us? Helioseismology is currently the best method for verifying stellar evolution
modelling theories and for understanding the structure and interior processes within the sun. It was able to rule out the possibility that the solar neutrino problem was due to incorrect models.
The sun speed is known to few parts per thounds over 90% of its radius.
Features revealed by helioseismology include that the outer convective zone and the inner radiative zone rotate at different speeds to generate the main magnetic field of the Sun the convective zone has jet streams of plasma thousands of kilometers below the surface.
Helioseismology can also be used to detect sunspots on the far side of the Sun from Earth.
Solar-like oscillations
Full disk observations
0
No rotation (splitting)
No inclination
l=1 l=
2
l=0
adapted image fromGizon & Solanki (2003)
Cen A
Bouchy & Carrier 2001
Butler et al. 2004
Solar-like oscillations in Red giants
Hydrae: Frandsen et al. (2002) Ophiuchi: De Ridder et al. (2006)
Solar-like oscillations in red giants
Structure: Density profile
Main sequence Post-main sequence: Central He-burning
Red Giants
Main sequence Post-main sequence: Central He-burning
p modesg modes
freq
uen
cy
freq
uen
cy
Radius time
Mixed Modes
Diagramme HR
Log
10L
/L
Log10Teff
0.8
0.6
11.2
3.88 3.86 3.84 3.82 3.8 3.78 3.76
Diagramme HR
Log
10L
/L
Log10Teff
0.8
0.6
11.2
3.88 3.86 3.84 3.82 3.8 3.78 3.76
Diagramme HR
Log
10L
/L
Log10Teff
0.8
0.6
11.2
3.88 3.86 3.84 3.82 3.8 3.78 3.76
Diagramme HR
Log
10L
/L
Log10Teff
0.8
0.6
11.2
3.88 3.86 3.84 3.82 3.8 3.78 3.76
Diagramme HR
Log
10L
/L
Log10Teff
0.8
0.6
11.2
3.88 3.86 3.84 3.82 3.8 3.78 3.76
Diagramme HR
Log
10L
/L
Log10Teff
0.8
0.6
11.2
3.88 3.86 3.84 3.82 3.8 3.78 3.76
Diagramme HR
Log
10L
/L
Log10Teff
0.8
0.6
11.2
3.88 3.86 3.84 3.82 3.8 3.78 3.76
Diagramme HR
Log
10L
/L
Log10Teff
0.8
0.6
11.2
3.88 3.86 3.84 3.82 3.8 3.78 3.76
Diagramme HR
Log
10L
/L
Log10Teff
0.8
0.6
11.2
3.88 3.86 3.84 3.82 3.8 3.78 3.76
Diagramme HR
Log
10L
/L
Log10Teff
0.8
0.6
11.2
3.88 3.86 3.84 3.82 3.8 3.78 3.76
Diagramme HR
Log
10L
/L
Log10Teff
0.8
0.6
11.2
3.88 3.86 3.84 3.82 3.8 3.78 3.76
Diagramme HR
Log
10L
/L
Log10Teff
0.8
0.6
11.2
3.88 3.86 3.84 3.82 3.8 3.78 3.76
Diagramme HR
Log
10L
/L
Log10Teff
0.8
0.6
11.2
3.88 3.86 3.84 3.82 3.8 3.78 3.76
H&H exercise 2003-2004: HD57006
h /R
r /R
r /R
Displacement function
l = 0
l = 1
Modes Evolution. Central He-burning phase.
E is the modes inertia, omega is the dimensionless frequency, Yc is the central He content
Non adiabatic code: MAD ( Dupret 2002) where W(M)=, and E is the inertia
Are non radial excited to observed amplitudes in red giants?
There are modes with inertia similar to that of a radial modes. In principle, this modes might be excited to an observable level throught stochastic excitation.
Hekker at al. (2006) found evidence that the modes in Oph had l=2.
Ongoing projects and future work
Space based: MOST, COROT, BRITE, Kepler
Ground based: SONG
Asteroseismology and Interferometry.
Asteroseismology as piece of the big astro puzzle
Helio- and asteroseismologySun:• Formation of the solar system• Solar Wind• Solar magnetic cycle
Atmosphere
LifeClusters
Galaxies
UniverseCosmology
Ages and Compositions
Weather
Stars:• Nuclear Reactions• Stellar evolution• Synthesize elements
Last word
....Our telescopes may probe farther and farther into the depths of space; but how can we ever obtain certain knowledge of that which is hidden behind substantila barriers? What appliance can pierce through the outer layers of a star and test the conditions within?
Eddington (1926):
