A Practical Introduction to Stellar Nonradial Oscillations (i) Rich Townsend University of Delaware ESO Chile ̶ November 2006
Download ReportTranscript A Practical Introduction to Stellar Nonradial Oscillations (i) Rich Townsend University of Delaware ESO Chile ̶ November 2006
A Practical Introduction to Stellar Nonradial Oscillations (i) Rich Townsend University 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 = 3 ℓ = 2 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)