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Astron. Astrophys. 346, L69-L72 (1999)

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Letter to the Editor

Electron temperature diagnostics for the quiet Sun using Si IV lines

S. Ahmed 1, D.J. Pinfield 1, M. Mathioudakis 1, F.P. Keenan 1, K.J.H. Phillips 2 and W. Curdt 3

1 Department of Pure and Applied Physics, The Queen's University of Belfast, Belfast BT7 1NN, Northern Ireland
2 Space Science Department, Rutherford Appleton Laboratory, Chilton, Didcot, Oxfordshire OX11 0QX, UK
3 Max-Planck-Institut für Aeronomie, D-37191 Katlenburg-Lindau, Germany

Received 29 March 1999 / Accepted 25 May 1999


We compare SUMER observations of six Si IV emission lines detected at the quiet Sun disk centre with recent theoretical line ratio calculations. Good agreement is found between theory and observation for ratios involving the 1394, 1403 and 818 Å line intensities. This agreement supports the theoretical prediction that the temperature where Si IV has its maximum ionisation fraction in ionisation equilibrium is [FORMULA] K, as well as showing that Lyman continuum absorption does not significantly effect line intensities for transitions with wavelengths below 912 Å. We find that the 815, 1122 and 1128 Å lines are blended by approximately 30, 55 and 45%, respectively, in the SUMER transitions.

Key words: atomic data – line: identification – Sun: transition region – Sun: UV radiation

Send offprint requests to: sa@star.pst.qub.ac.uk

© European Southern Observatory (ESO) 1999

Online publication: June 17, 1999