Accurate determination of electron densities from hydrogen line widths in active and quiescent prominences: The mid-infrared advantage Available to Purchase

We have measured the widths of all hydrogen lines in the MIR (8 to 20 micron) spectra of a quiescent and two time-frames of an active prominence. Accounting for instrumental and Doppler broadening, we attribute the remaining width to the sum of Stark contributions, which are shown to be due to protons in the quasi-static and to electrons in the impact limits. We obtain electron densities, $Ne=1.3(0.2),$ 5.2(0.8), and 2.2(0.4) in units of $1010 cm−3$ for the above 3 prominences respectively. For the quiescent prominence, our value is consistent with the lower end of the accepted range (Bommier) but not with those at the higher end (Hirayama, Nikolsky).