Transcript Solar-like oscillations in intermediate red giants

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?
frequency
Waves propagation in stars
Radius
P modes
G modes
For n>>l there is an asymptotic relation
saying that the modes are equally spaced
:
 ( Hz)
In frequency for p modes :
In period for g modes:
l

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=
l=
0
2
adapted image from
Gizon & Solanki (2003)
 Cen A
Butler et al. 2004
Bouchy & Carrier 2001
Solar-like oscillations in Red
giants
Solar-like oscillations in red giants
 Hydrae: Frandsen et al. (2002)
 Ophiuchi: De Ridder et al. (2006)
Structure: Density profile
Main sequence
Post-main sequence: Central He-burning
Red Giants
Main sequence
Post-main sequence: Central He-burning
g modes
p modes
frequency
frequency
Mixed Modes
Radius
time
1
0.8
0.6
0.6
H&H exercise 2003-2004: HD57006
Log10L/L
1.2
Diagramme HR
3.88
3.86
3.84
3.82
3.8
Log10Teff
3.78
3.76
r /R
h /R
Displacement function
r /R
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 asteroseismology
Sun:
• Formation of the solar system
• Solar Wind
• Solar magnetic cycle
Stars:
• Nuclear Reactions
• Stellar evolution
• Synthesize elements
Weather
Atmosphere
Life
Ages and Compositions
Clusters
Galaxies
Cosmology
Universe
Last word
Eddington (1926):
....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?