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Astron. Astrophys. 334, 685-702 (1998)

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Solar irradiances and radiances of UV and EUV lines during the minimum of sunspot activity in 1996

K. Wilhelm 1, P. Lemaire 2, I.E. Dammasch 1, J. Hollandt 3, U. Schühle 1, W. Curdt 1, T. Kucera 4, D.M. Hassler 5 and M.C.E. Huber 6

1 Max-Planck-Institut für Aeronomie, Max-Planck-Str. 2, D-37191 Katlenburg-Lindau, Germany
2 Institut d'Astrophysique Spatiale, Unité Mixte, CNRS-Université Paris XI, Bat 121, F-91405 Orsay, France
3 Physikalisch-Technische Bundesanstalt, Abbestrasse 2-12, D-10587 Berlin, Germany
4 Code 682.3, NASA/Goddard Space Flight Center (GSFC), Greenbelt, MD 20771, USA
5 Southwest Research Institute, 1050 Walnut St., Suite 426, Boulder, CO 80302, USA
6 European Space Agency (ESA), Space Science Department, ESTEC, 2200 AG Noordwijk, The Netherlands

Received 18 December 1997 / Accepted 9 February 1998


Full Sun observations in UV and EUV emission lines were performed by SUMER (Solar Ultraviolet Measurements of Emitted Radiation) on SOHO (Solar and Heliospheric Observatory) in 1996. The radiometric pre-flight calibration of SUMER is traceable to a primary radiometric source standard - the electron storage ring BESSY. Based on this calibration, the irradiance values at SOHO and at 1 AU have been obtained for the lines He I ([FORMULA] 584.33 Å), O V ([FORMULA] 629.74 Å), Ne VIII ([FORMULA] 770.41 Å), S V ([FORMULA] 786.47 Å), O IV ([FORMULA] 787.72 Å), S VI ([FORMULA] 933.39, 944.52 Å), H I Ly  [FORMULA] ([FORMULA] 937.80 Å), C III ([FORMULA] 977.04 Å), N V ([FORMULA] 1238.81 Å), Si I ([FORMULA] 1256.52 Å), and C IV ([FORMULA] 1548.20 Å). The spatially resolved measurements allowed good estimates to be made of the active region contributions to the irradiance of the quiet Sun. The centre-to-limb radiance variations of these lines have also been obtained from these measurements. For quiet solar conditions, a radiance spectrum was determined for wavelengths from 800 Å to 1500 Å near the centre of the solar disk.

Key words: Sun: corona – Sun:transition region – Sun: UV radiation – Sun: activity

Send offprint requests to: K. Wilhelm, (Wilhelm@linmpi.mpg. de).

© European Southern Observatory (ESO) 1998

Online publication: May 15, 1998