4 research outputs found
Non-thermal line-broadening in solar prominence
We show that the line broadening in quiescent solar prominences is mainly due
to non-thermal velocities. We have simultaneously observed a wide range of
optically thin lines in quiescent prominences, selected for bright and narrow
Mg\,b emission without line satellites from macro-shifts. We find a ratio of
reduced widths of H-gamma and H-delta of 1.05 +-0.03 which can hardly be
attributed to saturation, since both are optically thin for the prominences
observed: tau(gamma)<0.3 ; tau(delta)<0.15. We confirm the ratio of reduced
widths of He4772(triplet) and He5015(singlet of 1.1 +-0.05 at higher
significance and detect a width ratio of Mgb2 and Mg4571 (both from the triplet
system) of 1.3 +-0.1. The discrepant widths of lines from different atoms, and
even from the same atom, cannot be represented by a unique pair [T_kin ;
V_nth]. Values of T_kin deduced from observed line radiance using models,
indicate low temperatures down to T_kin~5000K. Non-thermal velocities, related
to different physical states of the respective emitting prominence region, seem
to be the most important line broadening mechanism
The Na I and Sr II Resonance Lines in Solar Prominences
We estimate the electron density, n_e, and its spatial variation in quiescent
prominences from the observed emission ratio of the resonance lines Na I 5890
(D2) and Sr II 4078. For a bright prominence (tau_alpha ~ 25) we obtain a mean
n_e ~ 2*10^10 /cm^3; for a faint one (tau_alpha ~ 4) n_e ~ 4*10^10 /cm^3 on two
consecutive days with moderate internal fluctuation and no systematic variation
with height above the solar limb. The thermal and non-thermal contributions to
the line broadening, T_kin and V_nth, required to deduce n_e from the emission
ratio NaI/SrII cannot be unambiguously determined from observed widths of lines
from atoms of different mass. The reduced widths, Delta-lambda_D / lambda_0, of
Sr II 4078 show an excess over those from NaD2 and H-delta, assuming the same
T_kin and V_nth. We attribute this excess broadening to higher non-thermal
broadening induced by interaction of ions with the prominence magnetic field.
This is suggested by the finding of higher macro-shifts of SrII4078 as compared
to those from NaD2.Comment: Solar Physics (in press
Helium Emissions Observed in Ground-Based Spectra of Solar Prominences
The only prominent line of singly ionized helium in the visible spectral
range, helium-II 4686 A, is observed together with the helium-I 5015 A singlet
and the helium-I 4471 A triplet line in solar prominences. The sodium emission,
NaD2, is used as a tracer for helium-II emissions which are sufficiently bright
to exceed the noise level near 10^-6 of the disk-center intensity. The so
selected prominences are characterized by small non-thermal line broadening and
almost absent velocity shifts, yielding narrow line profiles without wiggles.
The reduced widths [Delta(lambda_D) / lambda] of helium-II 4686 A are 1.5 times
broader than those of helium-I 4471 A triplet and 1.65 times broader than those
of helium-I 5015 A singlet. This indicates that the helium lines originate in a
prominence--corona transition region with outwards increasing temperature.Comment: 12 pages, 5 figure, 3 table