An intensity/linewidth analysis of opacity: first applications to a solar prominence and He II line profiles

Abstract

An analysis is described which can derive optical thicknesses and associated quantities from measured intensities and linewidths using convenient expressions for photon escape probabilities and for opacity‐broadened line halfwidths. An associated analysis of the effect of observational errors is provided. The analysis treats intensities and linewidths independently so that internal consistency of results can provide a measure of observational accuracy, which is shown here to be a stringent requirement. As examples, first applications are made to Si II lines in a solar prominence and to some high‐resolution observations of the solar He II 303.78‐Å resonance line.

Reliable Resonance Line Opacity Values by an Intensity/Linewidth Method Applied to Precise Data

“…Basically, the linewidth Dk thin of an appropriate optically thin line l thin must be measured to obtain Dv thin , and this is explicitly available in some cases. This will be referred to as the direct option (1). On the other hand, observers sometimes do not give such optically thin linewidths explicitly but instead give the derived non-thermal velocity V NT , or the equivalent velocity spread V thin may be given in km/s.…”

“…On the theoretical side, results for idealized source models have usually been di¤cult to apply to real spectra; and on the observational side, su¤ciently accurate linewidths and pro¢les have only recently become available for analysis. To connect theory with observations/ experiments more directly, the writer has recently developed an analysis which makes use of both intensities and linewidths [1] (KB), on the basis that both physical attributes need to be taken into account for a fully consistent treatment. The analysis particularly exploits pairs of lines having a common upper level.…”