Hydrogen Lyman-alpha and Lyman-beta spectral radiance profiles in the quiet Sun

TL;DR

This study analyzes hydrogen Lyman-alpha and Lyman-beta spectral profiles in the quiet Sun, revealing their asymmetries, absorption characteristics, and correlations with solar atmospheric flows, enhancing understanding of solar chromospheric and transition-region dynamics.

Contribution

It provides a detailed quantitative analysis of Lyman-alpha and Lyman-beta line profiles, including their asymmetries and relation to solar flows, extending previous observational work with new insights.

Findings

Most Ly-alpha profiles are self-reversed; about 17% of Ly-beta are not.

Lyman line emissions are more absorbed in the internetwork regions.

Profile asymmetries correlate with transition-region flows and Doppler shifts.

Abstract

We extend earlier work by studying in the quiet Sun the line profiles of the hydrogen Lyman-alpha and Lyman-beta lines, which were obtained quasi-simultaneously in a raster scan near disk center. The self-reversal depths of the Ly-a and Ly-b profiles are quantified by measuring the maximum spectral radiances of the two horns and the minimum spectral radiance of the central reversal. The information on the asymmetries of the Ly-a and Ly-b profiles is obtained through the calculation of the 1st and 3rd-order moments of the line profiles. We find that the emissions of the Lyman lines tend to be more strongly absorbed in the internetwork, as compared to those in the network region. Almost all of the Ly-a profiles are self-reversed, whilst about 17% of the Ly-b profiles are not reversed. The ratio of Ly-a and Ly-b intensities seems to be independent of the magnetic field strength. Most Ly-a profiles are stronger in the blue horn, while most Ly-b profiles are stronger in the red horn. However, the opposite asymmetries of Ly-a and Ly-b are not pixel-to-pixel correlated. We also confirm that when larger transition-region downflows are present, the Ly-a and Ly-b profiles are more enhanced in the blue and red horns, respectively. The first-order moment of Ly-b, which reflects the combined effects of the profile asymmetry and motion of the emitting material, strongly correlates with the Doppler shifts of the Si iii and O vi lines, whilst for Ly-a this correlation is much weaker. Our analysis shows that both Ly-a and Ly-b might be more redshifted if larger transition-region downflows are present. We also find that the observed average Ly-b profile is redshifted with respect to its rest position.