Research Note

On the origin of the Balmer and Lyman emission lines in solar prominences

¹ Institut d'Astrophysique (IAP), 98bis Bvd. d'Arago, 75014 Paris, France e-mail: stell@iap.fr
² Institut für Astrophysik, Universität Göttingen Friedrich-Hund-Platz 1, 37077 Göttingen, Germany e-mail: ewiehr@astro.physik.uni-goettingen.de

Received: 19 February 2008
Accepted: 9 July 2008

Abstract

Aims. We show how the observed hydrogen Balmer and Lyman emission lines constrain the modeling of quiescent solar prominences.

Methods. We compare space observations of Lyman lines with ground-based observations of Balmer lines for quiescent solar prominences of comparable brightness defined by their Hβ emission.

Results. The effective number densities of hydrogen atoms emitting from the same upper level u deduced from the corresponding emerging Lyman and Balmer line emissions show large differences that diminish with increasing level number and converge at the highest level numbers. Hydrogen atoms excited in contribute 250 times less, and those in still contribute 65 times less to the Lyman than to the corresponding Balmer emission, supporting the idea of distinct spatial origin of the emissions of both series. This is also indicated by the line widths. The high optical thickness of all Lyman members allows the brightness temperature T_b to be estimated from the spectral radiance at line center, where T_b is found to be largely independent of the upper level number, in contrast to the (known) behavior of the Balmer lines.