Hydrogen Ly-α and Ly-β full Sun line profiles observed with SUMER/SOHO (1996–2009)^⋆

¹ Institut d’Astrophysique Spatiale (IAS), Unité mixte CNRS-Université, Université Paris XI, bât.121, 91405 Orsay, France
e-mail: lemaire@ias.u-psud.fr
² Max-Planck-Institut für Sonnensystemforschung, Justus von-Leibig-Weg 3, 37077 Göttingen, Germany

Received: 9 March 2015
Accepted: 19 June 2015

Abstract

Context. Accurate hydrogen spectra emitted by the entire solar disc in the Ly-α and Ly-βlines are valuable for deriving the distribution and the behaviour of atomic hydrogen in the heliosphere, for understanding the UV emissions of solar type stars better, and finally for estimating the solar energy input that mainly initiates the chemical processes occurring in the planetary and cometary outer atmospheres.

Aims. In this paper we want to accurately determine the irradiance solar spectral profiles of Ly-α and Ly-β and their evolution through the solar activity cycle 23.

Methods. The SUMER/SOHO spectrometer is a slit spectrometer that is only able to analyse a small part of the solar image. Consequently, we used the scattered light properties of the telescope to obtain average spectra over the solar disc. Then the profile is calibrated using the SOLSTICE/UARS and TIMED/SEE irradiance spectra.

Results. We obtained a set of irradiance Ly-α and Ly-β solar spectra with a 0.002 nm resolution through the solar activity cycle 23. In each line a relation between the integrated profile and the line centre intensity was obtained.Knowing the line irradiance, it is possible to deduce the central line profile intensity, a critical input into the interplanetary and planetary oxygen and hydrogen fluorescent processes.

Conclusions. The observation of H i Ly-α and Ly-β line profiles by SUMER/SOHO during the cycle 23 allows analysis of the evolution of their characteristics and accurate determination of UV radiation input into the solar system.