A Practical Introduction to Stellar Nonradial Oscillations (i)

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A Practical Introduction to Stellar Nonradial
Oscillations (i)

• Rich Townsend
• University of Delaware

ESO Chile ? November 2006
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Overview

• Historical Perspective
• Radial pulsators
• Nonradial pulsators
• Waves in stars
• Global oscillations
• Surface variations
• Rotation effects
• Driving mechanisms

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p-mode Surface Variations
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g-mode Surface Variations
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p modes vs. g modes
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Carnot Cycle
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Excitation Mechanisms

• Add heat when temperature is high
• Remove heat when temperature is low
• Mechanisms
• ? opacity
• e nuclear energy
• d superadiabatic stratification
• ? ionization

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OPAL / OP Opacities
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5 M model
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WN model
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Brown Dwarf model
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Asteroseismology

• Compare observations against models
• Frequencies
• Multi-color light curve
• Amplitudes
• Phases
• Spectroscopy
• Line-profile variations
• Mean profiles

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Frequencies
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Photometric Amplitudes
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Line-Profile Variations
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lpv Time-Series
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Modeling

• Photometric
• Semi-analytical
• Spectroscopic
• Semi-analytical
• Moments
• TVS
• Numerical
• BRUCE/KYLIE
• PULSTAR

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Photometric Modeling

• Stamford Watson (1981)
• Semi-analytical formula for flux changes

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Photometry of SPB stars
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Spectroscopic Modeling

• Represent stellar surface with mesh
• Perturb mesh with pulsation(s)
• Rasterize mesh
• Synthesize spectra for each pixel
• Combine spectra

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Spectral Synthesis

• For each pixel
• Teff
• log g
• V
• ?
• Interpolate spectrum in intensity grid

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Pulsation Rotation

• Coriolis force becomes significant when ?/? gt 0.5
• Pulsation confined within equatorial waveguide
• New formula
• Townsend (2003)
• Extends Dziembowski (1977)
• Low-frequency (SPBs)

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Effects of Rotation