Time Domain Astrophysics in South Africa 2

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Time Domain Astrophysics in South Africa 2

• Astero-seismology

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Astero-seismology

• Monitoring Time variations in intrinsic variables
  in order to infer their properties such as mass,
  luminosity, rotation rate, internal composition

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Seismic Waves trapped in Stars

• Stars pulsate according to
• yAn( r ) Ylm (theta, phi) exp(-omega t)
• Where n l m describe a mode
• A good start to astero-seismology is in
  determining these for as many modes as possible

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Probing a star with seismic waves
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Asteroseismology Research in South Africa

• Observational Studies include
• - mode identification using photometry alone
  (determines l)
• - mode identification using Baade-Wesselink
  methods (combination)
• - mode-identification by observing line profile
  variations
• On roAp stars, delta Scuti, sdB stars, beta
  Cepheid etc

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Search for new Pulsating stars

• Rapidly Oscillating Ap stars (SAAO)
• 5 min lt Ppulslt16 min

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Frequency Spectrum
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Pulsating sdB stars

• hot Horizontal Branch stars with temperatures of
  about 30,000 K
• Periods 2 -3 minutes

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Observational Facilities

• Photo-electric photometers
• CCDs (also have frame-transfer)
• Giraffe spectrograph R 39000, wavelength 3820
  - 9240 angstrom, V lt 9
• SALT ?

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Theory

• Non-linear theory (SAAO)
• Radiative Transfer and Oscillations in A stars
  (UCT/SAAO)