Stellar oscillations across the H-R diagram

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Stellar oscillations across the H-R diagram
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Helioseismology

• Millions of independent oscillation frequencies
  excited simultaneously
• Each mode samples the interior in a different and
  complementary way
• This provides a detailed calibration of the
  physics of standard solar models

Larger
Smaller
? Surface spatial scale ?
Shallower
? Interior sampled ?
Deeper
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Calibrating solar physics

• New radiative opacities significantly improved
  standard solar models
• Models with settling of heavy elements agreed
  even more closely
• Remaining discrepancies in the outer layers were
  resolved by a new EOS

Dziembowski et al. (1992)
Bahcall et al. (1997)
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Asteroseismology

• New opportunities to probe the fundamental
  physics of the models
• Understanding the solar evolution in a broader
  context from stellar ages
• Only the lowest degree modes are detectable in
  distant stars (l lt 3)

Bedding Kjeldsen (2003)
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Observing techniques
Light variation
Appourchaux et al. (2008)
Velocity variation
Bouchy et al. (2004)
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Solar-like oscillations
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Mission SOHO

• SOlar and Heliospheric Observatory, launched in
  December 1995
• Sun-as-a-star data from VIRGO experiment, SPM and
  LOI instruments
• 5.5-cm aperture, silicon photodiode detectors

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Stellar density and age
Elsworth Thompson (2004)

• Large frequency spacing ltDngt scales with average
  density of the star
• Small frequency spacing ltdngt sensitive to
  interior gradients, proxy for age
• Probe evolution of activity and rotation as a
  function of stellar mass and radius

Christensen-Dalsgaard (2004)
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Mission WIRE

• Wide-field InfraRed Explorer, launched in March
  1999
• Primary instrument failed shortly after launch
  due to complete loss of coolant
• 5.2-cm star tracker with CCD camera mounted to
  side of main instrument

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Radial differential rotation

• WIRE 50-day time series of a Cen A has resolved
  the rotational splitting
• Splitting as a function of radial order can
  indirectly probe differential rotation
• Even low-degree modes allow rough inversions of
  the inner 30 of radius

Fletcher et al. (2006)
Gough Kosovichev (1993)
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Mission MOST

• Microvariability and Oscillations of STars,
  launched in June 2003
• 15-cm primary mirror, two CCD cameras with Fabry
  lens array for stability
• Up to two months per target, 100 duty cycle, few
  ppm photometry

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Surface differential rotation

• Three seasons of precise MOST photometry for the
  solar-type star k1 Ceti
• Latitudinal differential rotation pattern has
  same functional form as Sun
• Kepler will obtain similar rotation measurements
  for 105 solar-type stars

Ca HK period
Walker et al. (2007)
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Mission CoRoT

• French-led ESA mission, successfully launched in
  December 2006
• 28-cm primary mirror, two science CCDs for planet
  transits and seismology
• Interleaved 1-month and 5-month runs for 2.5 yrs,
  100 duty cycle

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Convection zone depth

• Expected seismic signal from a CoRoT 5-month
  observation of HD 49933
• Second differences (d2n) measure deviations from
  even frequency spacing
• Base of the convection zone and He ionization
  create oscillatory signals

Baglin et al. (2006)
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Mission Kepler

• NASA mission currently scheduled for launch in
  March 2009
• 105 square degrees just above galactic plane in
  the constellation Cygnus
• Single field for 4-6 years, 100,000 stars 30
  minute sampling, 512 at 1 minute

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Oscillations and magnetic cycles

• Solar p-mode shifts first detected in 1990,
  depend on frequency and degree
• Even the lowest degree solar p-modes are
  shifted by the magnetic cycle
• Unique constraints on the mechanism could come
  from asteroseismology

Libbrecht Woodard (1990)
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Cycle-induced frequency shifts

• Solar p-mode shifts show spread with degree and
  frequency dependence
• Normalizing shifts by our parametrization removes
  most of the dependencies
• Kepler will document similar shifts in hundreds
  of solar-type stars

Metcalfe et al. (2007)
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Red supergiants
Kiss et al. (2006)
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(p-)ressure and (g-)ravity
Montgomery Winget (1999)
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Excitation mechanisms
Dutch Open Telescope
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Intermediate-mass pulsators
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d Scuti stars
Breger et al. (2005)
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g Dor stars
Rowe et al. (2007)
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roAp stars
Kurtz et al. (2002, 2005)
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Massive pulsators
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SPB stars
Aerts et al. (2006)
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b Cep stars
Aerts et al. (2006)
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Subdwarf variables
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sdB stars
Fontaine et al. (2007)
Schuh et al. (2006)
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White dwarf variables
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DOV stars
Winget et al. (1991)
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DBV stars
Sullivan et al. (2008)
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DAV stars
Kanaan et al. (2005)
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