The hydrogen Balmer, Paschen, and Brackett series lines in quiescent prominences

Abstract

To calculate the Balmer, Paschen, and Brackett line intensities, we solved the statistical equilibrium equations for a twenty level plus continuum atom of hydrogen.

From the temperature, ionization, and the first three level populations of the prominence models deduced in a previous work we have calculated the populations of the twenty bound levels and the integrated intensities corresponding to the series mentioned above. The method was also applied to the Heasley and Mihalas theoretical models.

Since the Lyman series are optically thick, we have worked out two different options: (a) assume radiative balance in these lines and (b) correct the radiative rates by multiplying them with an integro-exponential function EI2 which depends on the line optical depth at the thread center. The first option is shown to be the more consistent.

The integrated line intensities from the Balmer series have been compared with the observations and a clear difference was noted between quiescent and active prominences in the sense that the active prominence case can not be well fitted with the available models.

To evaluate the influence of the pressure, the temperature, the thermal conduction coefficient and the turbulence, velocity on the spectrum we have compared the results from different models.

From this study we conclude that only the lines arising from the lower levels up to 8–10 can give us information about the physical parameters that characterized the solar prominences since the intensities from the higher members of the series depend only on atomic properties because of the small departures from LTE of the upper levels involved.