A Practical Introduction to Stellar Nonradial Oscillations (i)
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Transcript of A Practical Introduction to Stellar Nonradial Oscillations (i)
A Practical Introduction to Stellar Nonradial Oscillations (i)
Rich TownsendUniversity of Delaware
ESO Chile ! November 2006
Overview
• Historical Perspective– Radial pulsators– Nonradial pulsators
• Waves in stars• Global oscillations• Surface variations• Rotation effects• Driving mechanisms
p-mode Surface Variations
g-mode Surface Variations
p modes vs. g modes
Carnot Cycle
Excitation Mechanisms
• Add heat when temperature is high• Remove heat when temperature is
low• Mechanisms:
– κ : opacity– ε : nuclear energy– δ : superadiabatic stratification– γ : ionization
OPAL / OP Opacities
5 M¯ model
WN model
Brown Dwarf model
Asteroseismology
• Compare observations against models– Frequencies– Multi-color light curve
• Amplitudes• Phases
– Spectroscopy• Line-profile variations• Mean profiles
Frequencies
Photometric Amplitudes
ℓ = 1
ℓ = 2ℓ = 3
Line-Profile Variations
lpv: Time-Series
Modeling
• Photometric– Semi-analytical
• Spectroscopic– Semi-analytical
• Moments• TVS
– Numerical• BRUCE/KYLIE• PULSTAR
Photometric Modeling
• Stamford & Watson (1981)• Semi-analytical formula for flux
changes
Photometry of SPB stars
Spectroscopic Modeling
• Represent stellar surface with mesh• Perturb mesh with pulsation(s)• Rasterize mesh• Synthesize spectra for each pixel• Combine spectra
Spectral Synthesis
• For each pixel:– Teff– log g– V–
• Interpolate spectrum in intensity grid
Pulsation & Rotation
• Coriolis force becomes significant when Ω/ω > 0.5
• Pulsation confined within equatorial waveguide
• New formula– Townsend (2003)– Extends Dziembowski
(1977)– Low-frequency (SPBs)
Effects of Rotation
Townsend (2003)