P1253814574CFcsr

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Asteroseismology with the Kepler Mission
Travis Metcalfe (NCAR)
We are the stars which sing, We sing with our
light We are the birds of fire, We fly over the
sky. SONG OF THE STARS Algonquin Mythology
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• Why is asteroseismology important to the primary
  science goal of Kepler?
• Transit only gives radius of planet relative to
  the unknown stellar radius
• Asteroseismology will measure the stellar radius
  with a precision of 2-3

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• Why is asteroseismology important to the primary
  science goal of Kepler?
• Transit only gives radius of planet relative to
  the unknown stellar radius
• Asteroseismology will measure the stellar radius
  with a precision of 2-3

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Kepler mission overview

• NASA mission currently scheduled for launch in
  mid-February 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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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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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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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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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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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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Stellar modeling pipeline

• Genetic algorithm probes a broad range of
  possible model parameters
• 0.75 lt Mstar lt 1.75
• 0.002 lt Zinit lt 0.05
• 0.22 lt Yinit lt 0.32
• 1.0 lt amlt lt 3.0
• Finds optimal balance between asteroseismic and
  other constraints

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Application to BiSON data

• Fit to 36 frequencies with l 0-2 and
  constraints on temperature, luminosity
• Matches frequencies with scaled surface
  correction better than 0.6 mHz r.m.s.
• Temperature and age within 0.1, luminosity and
  radius within 0.4

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TeraGrid portal

• Web interface to specify observations with
  errors, or upload as a text file
• Specify parameter values to run one instance of
  the model, results archived
• Source code available for those with access to
  large cluster or supercomputer

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Summary

• Kepler needs asteroseismology to determine the
  absolute sizes of any potentially habitable
  Earth-like planets that may be discovered.
• The mission will yield a variety of data to
  calibrate dynamo models, sampling many different
  sets of physical conditions and evolutionary
  phases.
• A uniform analysis of the asteroseismic data will
  help minimize the systematic errors, facilitated
  by a TeraGrid-based community modeling tool.