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):