We have calculated the emission spectra of hydrogen and sodium atoms in the cool part of prominence models which satisfy simultaneously the constraints of radiative transfer, statistical equilibrium and charge-particle conservations.
In the considered range of our model parameters, emission strengths of Hc~ and NaI D lines increase with the temperature and the total number density. Low-pressure models raise the ionization rate highly but yield very weak NaI D line intensities, since these model prominences contain small amounts of free electrons and sodium atoms which have a deep relation with the formation of sodium lines. We find that sodium D lines should be emitted in the high pressure region of prominences, and that their intensities are difficult to attain in the cool core of any model prominence with a temperature as low as 4000 K. In order to explain consistently the spectral emissions of He and NaI D lines observed in quiescent prominences, a total number density higher than 4 x 1011 cm-a and a temperature over 5000 K are required at least in the cool part of prominences. * Contributions from the Kwasan and Hida Observatories, University of Kyoto, No. 282.