Abstract
We study spectral lines in exceptionally bright solar limb prominences with pronounced sodium and magnesium emission. We find that most prominences with significant NaD2 and Mgb2 emission show centrally reversed profiles of H-alpha and occasionally even of H-beta, which are are well reproduced by semi-infinite models. The maximum H-alpha source function corresponds to an excitation temperature of 3950 K, for pronounced central reversions 4000 K; the related optical thickness exceeds 10.0. The narrow widths of the NaD2 and Mgb2 profiles yield a non-thermal broadening of 5 km/s.
Highlights
The simultaneous emission of resonance lines with low ionization potential, like Mgb2 and NaD2, and of hydrogen and helium with much higher excitation and ionization energies, illustrates the large deviations from LTE in atmospheres of solar prominences
We find that most prominences with significant NaD2 and Mgb2 emissions show pronounced centrally reversed Hα profiles, and occasionally even of Hβ; the strongest emissions reach integrated intensities Eβ > 16 × 104 [erg/(cm2 s str)]
High precision data of spectral prominence photometry show for faint emissions (Eβ ≤ 1 × 104 erg/(cm2 s str), corresponding to τα ≤ 1) a unique empirical relation between Hα and Hβ independent on the individual prominence atmospheres (Stellmacher & Wiehr 1994b). This relation depends on the prominence atmospheres
Summary
The simultaneous emission of resonance lines with low ionization potential, like Mgb and NaD2, and of hydrogen and helium with much higher excitation and ionization energies, illustrates the large deviations from LTE in atmospheres of solar prominences. High precision data of spectral prominence photometry show for faint emissions (Eβ ≤ 1 × 104 erg/(cm s str), corresponding to τα ≤ 1) a unique empirical relation between Hα and Hβ independent on the individual prominence atmospheres (Stellmacher & Wiehr 1994b). For higher emissions, this relation depends on the prominence atmospheres. The present observations are considered as an extension toward strongest emissions Eβ > 4 × 104 erg/(cm s str) Such bright prominences are known to be cool, dense, and rather unstructured (Stellmacher & Wiehr 1995). They allow a determination of upper limits of the source function of Hα as well as a quantitative analysis of the centrally reversed Hα profiles and their representation by models
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