Flare observation of the Sun as a star by SUMER/SOHO in the hydrogen Lyman continuum^*

¹ Institut d'Astrophysique Spatiale (IAS), Unité mixte CNRS-Université, Université de Paris XI, Bât. 121, 91405 Orsay, France
² Max-Planck-Institut für Aeronomie, 37191 Katlenburg-Lindau, Germany

Corresponding author: P. Lemaire, lemaire@ias.u-psud.fr

Received: 26 September 2003
Accepted: 4 February 2004

Abstract

During the execution of the programme “Sun as a star”, while the SUMER (Solar Ultraviolet Emission of Emitted Radiation)/SOHO (SOlar and Heliospheric Observatory) slit was collecting the scattered radiation from the telescope mirror far away from the solar disk image, a class X5.3/3b flare erupted on the solar disk, on 25 August 2001. During the first phase of the flare a relative increase of a few percent was detected at the head of the hydrogen Lyman continuum. After correction from the instrumental parameters, the relative signal increase is 70% at the head of the Lyman continuum (910 Å), and 190% in the C ii 904 Å multiplet. Accounting for the area of the flare region, the local increase of the radiance of the Lyman continuum and of the C ii lines is estimated to be a factor of several thousands. We compare this result with other solar observations and models.