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Hyperfine induced transitions as diagnostics of isotopic composition and densities of low-density plasmas

In English

Författare

  • Tomas Brage
  • PG Judge
  • A Aboussaid
  • MR Godefroid
  • P Jonsson
  • A Ynnerman
  • CF Fischer
  • DS Leckrone

Summary, in English

The J = 0 --> J' = 0 radiative transitions, usually viewed as allowed through two-photon decay, may also be induced by the hyperfine (HPF) interaction in atoms or ions having a nonzero nuclear spin. We compute new and review existing decay rates for the nsnp P-3(J)0 --> nS(2 1)S(J'= 0) transitions in ions of the Be (n = 2) and Mg (n = 3) isoelectronic sequences. The HPF induced decay rates for the J = 0 --> J' = 0 transitions are many orders of magnitude larger than those for the competing two-photon processes, and when present are typically 1 or 2 orders of magnitude smaller than the decay rates of the magnetic quadrupole (J = 2 --> J' = 0) transitions for these ions. Several HPF induced transitions are potentially of astrophysical interest in ions of C, N, Na, Mg, Al, Si, K, Cr, Fe, and Ni. We highlight those cases that may be of particular diagnostic value for determining isotopic abundance ratios and/or electron densities from UV or EUV emission-line data. We present our atomic data in the form of scaling laws so that, given the isotopic nuclear spin and magnetic moment, a simple expression yields estimates for HPF induced decay rates. We examine some UV and EUV solar and nebular data in light of these new results and suggest possible applications for future study. We could not find evidence for the existence of HPF induced lines in the spectra we examined, but we demonstrate that existing data have come close to providing interesting upper limits. For the planetary nebula SMC N2, we derive an upper limit of 0.1 for C-13/C-12 from Goddard High-Resolution Spectrograph data obtained by Clegg. It is likely that more stringent limits could be obtained using newer data with higher sensitivities in a variety of objects.

Publiceringsår

1998

Språk

Engelska

Sidor

507-521

Publikation/Tidskrift/Serie

Astrophysical Journal

Volym

500

Issue

1

Dokumenttyp

Artikel i tidskrift

Förlag

American Astronomical Society

Ämne

  • Physical Sciences

Nyckelord

  • atomic processes
  • plasmas
  • radiative transfer

Status

Published

ISBN/ISSN/Övrigt

  • ISSN: 0004-637X