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Experimental oscillator strengths for forbidden lines in complex spectra

In English

Författare

  • Henrik Hartman
  • Sveneric Johansson
  • Hans Lundberg
  • P Lundin
  • S Mannervik
  • P Schef

Summary, in English

In dilute astrophysical plasmas, such as planetary nebulae and H II regions, strong lines appear that only have weak, if any, correspondence to the spectrum of laboratory light sources. Some of these are parity forbidden lines, i.e. emission from long-lived metastable states that cannot decay via normal electric dipole (E1) routes but only via the slower M1 and E2 transitions. The long lifetime of the upper levels and their sensitivity to collisions make the lines good diagnostics of the emitting plasma, but then the transition probability, or A-value, of these lines must be known. We report on a technique to experimentally determine A-values for forbidden lines using the method of combining the lifetime of the upper level with the branching fractions for the different decay channels. The lifetime is measured using the laser probing technique (LPT) on a stored ion beam. Since these lines are rarely produced in laboratory plasmas, we use astrophysical spectra to determine the branching fractions (BF). The lifetime and the BF then give the A-value, which is one quantity needed for modeling the spectrum of the plasma emitting the forbidden lines. The present measurements are performed within the FERRUM project, an international collaboration producing and evaluating transition probabilities for iron group element lines of astrophysical importance [Johansson, P. I. S. et al., Physica Scripta T100, 71 (2002).]

Publiceringsår

2005

Språk

Engelska

Sidor

40-44

Publikation/Tidskrift/Serie

Physica Scripta

Volym

T119

Dokumenttyp

Konferensbidrag

Förlag

IOP Publishing

Ämne

  • Astronomy, Astrophysics and Cosmology

Nyckelord

  • Transition probability
  • Decay channels
  • Electric dipole
  • Branching fractions

Conference name

8th International Colloquium on Atomic Spectra and Oscillator Strenghts, ASOS 8

Conference date

2004-08-08 - 2004-08-12

Conference place

Madison, WI, United States

Status

Published

ISBN/ISSN/Övrigt

  • ISSN: 0281-1847