Contributed Talk - Splinter Solar

Wednesday, 23 September 2020, 12:15   (virtual room L)

Quiet-sun hydrogen Lyman-alpha line profile derived from SOHO/SUMER solar-disk observations

S. GunĂ¡r (1), P. Schwartz (2), J. Koza (2) and P. Heinzel (1)
(1) Astronomical Institute of the Czech Academy of Sciences; (2) Astronomical Institute of Slovak Ac

The solar radiation in the Lyman-alpha spectral line of hydrogen plays a significant role in the illumination of chromospheric and coronal structures, such as prominences/filaments, spicules, chromospheric fibrils, cores of coronal mass ejections, or solar wind. Moreover, it is important for the investigation of the heliosphere, Earth ionosphere, and the atmospheres of planets, moons and comets. We use SOHO/SUMER Lyman-alpha raster scans obtained without the use of the SUMER attenuator in various quiet-sun regions on the solar disk to derive a reference quiet-sun Lyman-alpha spectral profile. This reference profile is representative of the Lyman-alpha radiation from the solar disk during a minimum of solar activity. The solar radiation in the Lyman lines is not constant over time but varies significantly with the solar cycle. We use the LISIRD Composite Lyman-alpha index to adapt the incident radiation Lyman line profiles (Lyman-alpha and higher lines) to a specific date. Moreover, we estimate how the change of the incident radiation influences the synthetic spectra produced by the radiative transfer modelling. To do so, we use a 2D prominence fine structure model. The analysis of the influence of the change of the incident radiation shows that the synthetic spectra are strongly affected by the modification of the incident-radiation boundary condition in the Lyman lines. The most pronounced impact is on the central and integrated intensities of the Lyman lines.There, the change of the synthetic spectra can often have the same amplitude as the change of the incident radiation itself. The impact on the specific intensities in the peaks of reversed Lyman-line profiles is smaller but still significant. Interestingly, the hydrogen H-alpha line can be also affected considerably, even though the H-alpha radiation from the solar disk does not vary with the solar cycle.