The Influence of Fluctuations of the Solar Emission Line Profileon the Doppler Shift of Interplanetary HLyα Lines Observed by the Hubble–Space–Telescope

In an earlier research the employment of a radiation transport model with angle-dependent partial frequency redistribution, self-absorption by interplanetary hydrogen, realistic solar HLyαemission profile, and a time dependent `hot' hydrogen model to analyze 5 interplanetary HLyα glow spectra obtained with theHubble–Space–Telescope–GHRS spectrometer, has not resulted in unequivocal determination of a set of thermodynamical parameters of the interstellar hydrogen The residual discrepancies between the model and the data concern the observations performed within an interval of 1 year close to the solar minimum from very similar lines of sight. In this paper we investigate by calculating interplanetary HLyα lines with the use of a one hydrogen distribution and several solar HLyα line profiles whether this residual may be caused by possible variations in time of the shape of the solar HLyα emission line profile which cause variable illuminations of the interplanetary gas. These variations of illuminations cause variations in Doppler shift of the resonant interplanetary HLyα line that can amount to ≃ 4 km s-1in the line peak. Consequently we conclude that without adequate knowledge of the solar HLyα emission line profile during spectral observations of the interplanetary hydrogen gas it is impossible to obtain an agreement between models and observations better than by this value.