Assessing Atomic Models for Forbidden Transitions

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Assessing Atomic Models for Forbidden Transitions

• Dr Peter Young
• CCLRC/Rutherford Appleton Laboratory, UK
• and the CHIANTI team

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Background

• Astrophysical applications now account for around
  1/3 of citations to the CHIANTI papers
• B. Ercolano (UCL) expressed interest in including
  CHIANTI data in the MOCASSIN photoionization code
• CHIANTI has been optimized for the study of
  electron-ionized plasmas
• Do we have the best data for forbidden
  transitions at low temperatures?

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MOCASSIN Comparison
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CHIANTI data

• CHIANTI has been optimised for electron-ionized
  plasmas
• CHIANTI does not contain the original upsilon
  data, only fits to the Burgess Tully scaled
  upsilons
• Up to version 4, five point splines were fit to
  the data

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9 point splines

• Up to version 4 of CHIANTI, only 5 point splines
  were allowed to fit the collision data
• With version 4, the option of 9 point splines was
  allowed for hard to fit collision strengths
• Some early data have been re-fit with the 9-point
  splines to yield better accuracy at low
  temperatures

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Example Mg VII

• Currently DW data of Bhatia Doschek (1995) in
  CHIANTI
• IP data available for ground transitions (Lennon
  Burke 1994)
• only goes up to 105 K
• Mg VII formed at 6 x 105 K in electron ionized
  plasma

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Summary

• A number of CHIANTI forbidden transitions have to
  be re-assessed to ensure full temperature range
  of upsilons is represented
• Also have to ensure the best R-matrix
  calculations are being used, even if this means
  merging with other data-sets
• Improved forbidden transitions will go into v.6
  of CHIANTI