Detection of FIP Effect on Late-type Giants

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Detection of FIP Effect on Late-type Giants

• Coronal Abundances and Thermal Structure
• The late-type giants b Ceti, 31 Com and mVel
• Objects and Observations features
• The DEMs and Coronal Abundances
• Conclusions

D. Garcia-Alvarez, J.J. Drake, L.Lin, V. Kashyap
and B.Ball Smithsonian Astrophysical Observatory
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Coronal Abundances and Thermal Structure
Why derive Stellar Coronal Abundances?

• Abundance anomalies (FIP and inverse-FIP effect,
  flares).
• Larger range of stars is needed.
• It will help to interpret X-ray observations of
  stars.

Why/how to derive the Coronal Thermal Structure?

• Key to understanding the coronal heating.
• Must be known before elemental abundances can
  be determined.
• Abundance-independent structure obtained by
  using ratios of ions from same element.

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The MCMCM Method

• INPUTS
• Strong lines with the best atomic data (H-like
  and He-like and Fe ions).
• Line ratios from different ions of the same
  element.
• Continuum points are use to normalize model
  continua computed using a test DEM.
• THE CODE
• Markov-Chain Monte-Carlo simulations using a
  Metropolis algorithm (Kashyap Drake 1998).
• THE OUTPUT
• Abundance-independent DEM.
• Estimation of uncertainties and no artificial
  smoothing constrains on the derived DEM.

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Objects and Observations Features
Stellar photospheric abundances
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The Observed Spectra
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The Differential Emission Measurements

• Same slope/shape for the low temperature range.
• A plateau around log TK6.80.2 is observed in
  ? Ceti and ? Vel.
• Smooth increase and peak at log TK7.1 is
  observed in 31 Com.
• Little evidence for substantial amount of plasma
  at log TKgt7.3.

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The Synthetic Spectrum
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Finally the Coronal Abundances
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? Ceti 31 Com Capella ?
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Conclusions

• The late-type giants ? Ceti, 31 Com and ? Vel
  share similarities in coronal composition.
• We detected a solar-like FIP effect for ? Ceti
  and ? Vel but not for 31 Com.
• No clear dependency between rotational velocity
  and FIP trend.
• Structural changes during their evolution might
  produce the observed coronal pattern in late-type
  giants.