A Study of Solar Prominences near lambda = 1 Millimeter

Details A Study of Solar Prominences near lambda = 1 Millimeter A Study of Solar Prominences near lambda = 1 Millimeter

Nov 1993

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993apj...418..510b&link_type=abstract

Astrophysical Journal v.418, p.510

Astronomy and Astrophysics

Astronomy

10

Sun: Chromosphere, Sun: Prominences, Sun: Radio Radiation

Scientific paper

The 10.4 m Leighton telescope at the Caltech Submillimeter Observatory was used to produce full-disk and partial area raster maps of the Sun during 1991 July 9-11 in advance of the total eclipse of the Sun on July 11. Maps were made at a wavelength of 850 microns with an angular resolution of 20".6 and at 1250 microns with an angular resolution of 30".
We have analyzed the 850 microns brightness associated with Hα filaments present on the disk and find that (1) they are all associated with regions possessing a brightness comparable to or below that of the quiet Sun at the center of the disk; and (2) because of their lack of contrast with the background brightness distribution, Hα filaments are optically thin at 850 μm. We have also analyzed contemporaneous observations of a prominence above the solar limb at both 850 and 1250 mum. We show that (1) the optical depth of the prominence is τ ≍ 0.12 at 850 μm, confirming the conclusion drawn from the analysis of Hα filaments; and (2) the line-of- sight emission measure is = 1.3-2.0 × 1029 cm-5, and the electron number density is ne ˜ 1-3 × 1010 cm-3.
We argue that the reduced 850 microns brightness associated with Hα filaments and, more generally, magnetic neutral lines is due neither to the presence of an overlying coronal cavity nor to the presence of absorbing material, as has been suggested previously. We instead suggest that the reduced brightness is due to the structure of the underlying chromosphere where, in the case of filament channels, the predominantly horizontal magnetic field leads to a reduction of heating and/or a smaller density scale height.

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