The Role of Velocity Redistribution in Enhancing the Intensity of the HE II 304 Å Line in the Quiet-Sun Spectrum

Details The Role of Velocity Redistribution in Enhancing the Intensity of the HE II 304 Å Line in the Quiet-Sun Spectrum The Role of Velocity Redistribution in Enhancing the Intensity of the HE II 304 Å Line in the Quiet-Sun Spectrum

May 2000

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2000apj...535..438a&link_type=abstract

The Astrophysical Journal, Volume 535, Issue 1, pp. 438-453.

Astronomy and Astrophysics

Astronomy

20

Line: Formation, Line: Profiles, Sun: Atmospheric Motions, Sun: Chromosphere, Sun: Corona, Sun: Transition Region

Scientific paper

We present observational evidence of the effect of small-scale (``microturbulent'') velocities in enhancing the intensity of the He II λ304 line with respect to other transition region emission lines, a process we call ``velocity redistribution,''. We first show results from the 1991 and 1993 flights of SERTS (Solar EUV Rocket Telescope and Spectrograph). The spectral resolution of the SERTS instrument was sufficient to infer that, at the spatial resolution of 5", the line profile is nearly Gaussian both in the quiet Sun and in active regions. We were then able to determine, for the quiet Sun, a lower limit for the amplitude of nonthermal motions in the region of formation of the 304 Å line of the order of 10 km s-1. We estimated that, in the presence of the steep temperature gradients of the solar transition region (TR), velocities of this magnitude can significantly enhance the intensity of that line, thus at least helping to bridge the gap between calculated and observed values. We also estimated the functional dependence of such an enhancement on the relevant parameters (nonthermal velocities, temperature gradient, and pressure). We then present results from a coordinated campaign, using SOHO/CDS and Hα spectroheliograms from Coimbra Observatory, aimed at determining the relationship between regions of enhanced helium emission and chromospheric velocity fields and transition region emission in the quiescent atmosphere. Using these data, we examined the behavior of the He II λ304 line in the quiet-Sun supergranular network and compared it with other TR lines, in particular with O III λ600. We also examined the association of 304 Å emission with the so-called coarse dark mottle, chromospheric structures seen in Hα red-wing images and associated with spicules. We found that all these observations are consistent with the velocity redistribution picture.

Affiliated with

Also associated with

No associations

Rating

The Role of Velocity Redistribution in Enhancing the Intensity of the HE II 304 Å Line in the Quiet-Sun Spectrum does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.

If you have personal experience with The Role of Velocity Redistribution in Enhancing the Intensity of the HE II 304 Å Line in the Quiet-Sun Spectrum, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and The Role of Velocity Redistribution in Enhancing the Intensity of the HE II 304 Å Line in the Quiet-Sun Spectrum will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFWR-SCP-O-1127560