Nicolas Labrosse, Kristopher McGlinchey
Context. Theoretical calculations have shown that when solar prominences move
away from the surface of the Sun, their radiative output is affected via the
Doppler dimming or brightening effects. Aims. In this paper we ask whether
observational signatures of the changes in the radiative output of eruptive
prominences can be found in EUV (extreme ultraviolet) observations of the first
resonance line of ionised helium at 304 {\AA}. We also investigate whether
these observations can be used to perform a diagnostic of the plasma of the
eruptive prominence. Methods. We first look for suitable events in the SDO/AIA
database. The variation of intensity of arbitrarily selected features in the
304 channel is studied as a function of velocity in the plane of the sky. These
results are then compared with new non-LTE radiative transfer calculations of
the intensity of the He II 304 resonance line. Results. We find that
observations of intensities in various parts of the four eruptive prominences
studied here are sometimes consistent with the Doppler dimming effect on the He
II 304 {\AA} line. However, in some cases, one observes an increase in
intensity in the 304 channel with velocity, in contradiction to what is
expected from the Doppler dimming effect alone. The use of the non-LTE models
allows us to explain the different behaviour of the intensity by changes in the
plasma parameters inside the prominence, in particular the column mass of the
plasma and its temperature. Conclusions. The non-LTE models used here are more
realistic than what was used in previous calculations. They are able to
reproduce qualitatively the range of observations from SDO/AIA analysed in this
study. Thanks to non-LTE modelling, we can infer the plasma parameters in
eruptive prominences from SDO/AIA observations at 304 {\AA}.
View original:
http://arxiv.org/abs/1111.4847
No comments:
Post a Comment