Helioseismology and Asteroseismology: Sounding Stars · Asteroseismology: Sounding Stars Professor...
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Helioseismology and Asteroseismology: Sounding Stars Professor Bill Chaplin, School of Physics & Astronomy University of Birmingham, UK Science on the Sphere Royal Society Meeting, 15 July 2014
Transcript of Helioseismology and Asteroseismology: Sounding Stars · Asteroseismology: Sounding Stars Professor...
Helioseismology and Asteroseismology:
Sounding Stars
Professor Bill Chaplin, School of Physics & Astronomy University of Birmingham, UK
Science on the Sphere Royal Society Meeting, 15 July 2014
helioseismology, n. The study of the sun's interior by the observation and analysis of oscillations at its surface. Cf. asteroseismology n. [Oxford English Dictionary]
The Birmingham Solar Oscillations Network BiSON
Gary Larson
“Inside the Sun”
asteroseismology, n. The study of the interior of stars by the observation and analysis of oscillations at their surface. Cf. helioseismology n. [Oxford English Dictionary]
Solar-like oscillations Stochastically excited and intrinsically damped by near-surface convection
Standing acoustic waves Internal acoustic
ray paths Surface displacement:
oscillation patterns in 3D
red waves give…
blue waves give…
In rapidly rotating stars…
Island Chaotic “Whispering gallery”
Moo
Spherical Harmonics (l,m) 1,0 1,1 2,0
2,1 2,2 3,0
3,1 3,2 3,3
5,5 10,5 10,10
Spherical Harmonics (l,m)
n Fundamental period of radial pulsation: 2/1−
∝Π ρ
n Estimate period from sound crossing time
n Period similar to dynamical timescale (‘free fall’ time)
Ritter 1880; Shapley, 1914
Pulsation timescale
Courtesy D. Hathaway
Sun: fundamental radial-mode period
Π f ≈ 1 hour
ν f ≈ 250 µHz
Pulsation timescale
Frequency spectrum of low-degree (low-l) modes (contains overtones of 0 ≤ l ≤ 3)
BiSON data
High-overtone (n ≈20) modes!
250 µHz
l=2
l=0
l=2
l=0
l=2
l=1
l=0 l=1
l=1
l=3 l=3
BiSON data
How are overtones of different degree, l, arranged in frequency?
Ridge
Overtone, n, increasing
Angular degree
Frequency
Overtones of given l
Frequency spectrum: l-ν diagram Consider the overtones of each degree, l
Frequency spectrum:
l-ν diagram Data collected
by MDI instrument on board SOHO
Frequency spectrum: uniform non-rotating sphere
)2/()2(4
lnlnRc
nl +Δ≈+≈ νν
Rc2
=Δν
Clamped boundary conditions: displacement fixed to zero at centre, edge
Frequency spectrum: uniform non-rotating sphere
⎟⎠
⎞⎜⎝
⎛++Δ≈⎟
⎠
⎞⎜⎝
⎛++≈
412/
212
4lnln
Rc
nl νν
Rc2
=Δν
Free boundary conditions: edges free
Frequency spectrum: uniform non-rotating sphere
General form
⎟⎠
⎞⎜⎝
⎛++Δ≈ ενν
2lnnl
Frequency spectrum: Star Stratified interior
)1(2
+−⎟⎠
⎞⎜⎝
⎛++Δ≈ lDllnnl ενν
Frequency spectrum: Rotating Star
Stratified interior, slow rotation approx.
rot)1(2
νενν Δ++−⎟⎠
⎞⎜⎝
⎛++Δ≈ mlDllnnlm
l=2
l=0
l=2
l=0
l=2
l=1
l=0 l=1
l=1
l=3 l=3
BiSON data
How are overtones of different degree, l, arranged in frequency?
)1(2
+−⎟⎠
⎞⎜⎝
⎛++Δ≈ lDllnnl ενν
Échelle frequency plot BiSON Sun-as-a-star + model frequencies
Kepler’s “best in class” The A-component of the solar-type binary 16 Cyg
Kepler’s “best in class” The A-component of the solar-type binary 16 Cyg
Sun SOHO
6116048
6603624
6106415
8379927
8006161 Doris
Arthur
Perky
Sun??
Saxo
Nunny
“Getting High⎯ Confessions of a Peak-Bagging
Junkie”
Toward automated peak-bagging of Sun-like stars
Appourchaux et al., 2012, A&A, 543, A54
Homogeneous analysis of 61 solar-type stars
Fractional sound-speed differences: observed minus model BiSON + MDI data
Basu et al., 2009, ApJ, 699, 1403
Internal Solar Rotation
GONG data
Rotation of the Deep Interior
Period of 26.6 days
Fractional radius
Rotational frequency
Ω/2π (nHz)
24.6 days
31.3 days
BiSON + SOI/MDI data
?
Spin-orbit alignment Asteroseismology constrains inclination
of stellar spin axis
The “transit method” Detection of extra-solar planets
Inference on stellar inclination Example: dipole mode of oscillation
A. Miglio
Kepler-50 and Kepler-65 Two stars with multiple small planets
Chaplin et al., 2013, ApJ, 766, 101
Inference on stellar inclination
Chaplin et al., 2013, ApJ, 766, 101
Example: dipole oscillation mode
Chaplin et al., 2013, ApJ, 766, 101
Kepler-50 and Kepler-65 Two stars with multiple small planets
Chaplin et al., 2013, ApJ, 766, 101
Internal rotation of a subgiant Core rotates five-times faster than surface
Deheuvels et al., 2012, ApJ, 756, 19
Huber et al., 2013, Science, 342, 331
Kepler-56 A misaligned multi-planet system
with a red-giant host star
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