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Astron. Astrophys. 320, 333-341 (1997)


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UV and soft X-ray lines from Fe XVI observed in solar and stellar spectra

M. Cornille 1, J. Dubau 1, H.E. Mason 2, C. Blancard 3 and W.A. Brown 4

1 Observatoire de Paris, UPR 176 CNRS, DARC F-92195 Meudon-Cedex, France
2 Department of Applied Mathematics and Theoretical Physics, Silver Street, CAMBRIDGE CB3 9EW, UK
3 Centre d'Etudes de Limeil-Valenton, F-94195 Villeneuve Saint Georges Cedex, France
4 Lockheed Palo Alto Research Laboratory, Palo Alto California 94304, USA

Received 27 June 1996 / Accepted 12 September 1996

Abstract

The ion Fe XVI is abundant in solar active regions and flares. Strong spectral lines from this ion have been observed over a wide wavelength range. The transitions 3s - 3p and 3p - 3d fall between 250 and 365Å and lines from transitions between n=3 to n=4, n=3 to n=5 fall between 30 and 80 Å. In this paper, we present distorted wave results for the electron scattering collision strengths from the ground level to all the other levels and discuss previous calculations. We compare our theoretical intensity ratios with solar observations and show that the strongest spectral lines in the X-ray wavelength range do not correspond to the dipole transitions, 3s - 4p, 3s - 5p, as might be expected. We comment on the approximations which have been generally used in synthetic spectrum programs to simulate the Fe XVI spectral line intensities and the consequences for analyses of solar and stellar spectra.

Key words: atomic data – Sun: corona – Sun: UV – stars: coronae – ultraviolet: stars

Send offprint requests to: M. Cornille

© European Southern Observatory (ESO) 1997

Online publication: July 3, 1998

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