Solar Lyman irradiance line profiles

Accurate hydrogen spectra emitted by the entire solar disc in the Ly-{alpha} and Ly-{beta} lines 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. In this paper we want to accurately determine the irradiance solar spectral profiles of Ly-{alpha} and Ly-{beta} and their evolution through the solar activity cycle 23.

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.