Synthetic hydrogen spectra of prominence oscillations

¹ Astronomical Institute, Academy of Sciences, 25165 Ondřejov, Czech Republic
e-mail: pheinzel@asu.cas.cz
² Departament de Física, Universitat de les Illes Balears, 07122 Palma de Mallorca, Spain
e-mail: maciej.zapior@uib.es; ramon.oliver@uib.es; joseluis.ballester@uib.es

Received: 23 July 2013
Accepted: 21 November 2013

Abstract

Context. Prominence oscillations have been mostly detected using Doppler velocity, although there are also claimed detections by means of periodic variations in half-width or line intensity. However, scarce observational evidence exists about simultaneous detection of oscillations in several spectral indicators.

Aims. Our main aim here is to explore the relationship between spectral indicators, such as Doppler shift, line intensity, and line half-width, and the linear perturbations excited in a simple prominence model.

Methods. Our equilibrium background model consists of a bounded, homogeneous slab, which is permeated by a transverse magnetic field, having prominence-like physical properties. Assuming linear perturbations, the dispersion relation for fast and slow modes has been derived, as well as the perturbations for the different physical quantities. These perturbations have been used as the input variables in a one-dimensional radiative transfer code, which calculates the full spectral profile of the hydrogen Hα and Hβ lines.

Results. We have found that different oscillatory modes produce spectral indicator variations in different magnitudes. Detectable variations in the Doppler velocity were found for the fundamental slow mode only. Substantial variations in the Hβ line intensity were found for specific modes. Other modes lead to lower and even undetectable parameter variations.

Conclusions. To perform prominence seismology, analysis of the Hα and Hβ spectral line parameters could be a good tool to detect and identify oscillatory modes.