Single Active Region Research Articles

On the Differences at Chromospheric Levels between RS Cvn-Type Binaries, Active and Quiet Chromosphere Single Stars, and Active and Quiet Regions in The Sun

RS CVn-type systems exhibit many similarities to active regions on the Sun. In the last few years considerable progress has been made in quantifying the differences between the atmospheric properties of solar plages and quiet regions. These differences, as summarized in Linsky’s (1979) review, can be simply explained by additional nonradiative heating and include the following: (1) temperature enhancements in the photosphere, (2) heating of the temperature minimum and its displacement downward in mass column density, (3) enhanced radiative losses in the chromosphere and transition region (typically by a factor of 10), (4) steeper chromospheric temperature gradients, and (5) enhanced pressures and densities at the top of the chromosphere, throughout the transition region, and at the base of the corona (again typically by a factor of 10).

Braided Structures Observed in Flare-Associated Hα Filaments

The motions of flare-associated filaments and prominences produce such large Doppler shifts that the morphology of these active phenomena cannot be studied without filtergrams taken in rapid succession at a number of wavelengths across the Hα line. It is therefore standard practice at the Ottawa River Solar Observatory (ORSO) to photograph single active regions through a Zeiss filter while the pass-band (0.25A) of the filter is stepped continously back and forth across the Hα line. A typical scan consists of 17 steps in the range Hα ± 1.4A and is completed in 42 seconds. Important by-products result from this procedure, especially when the seeing allows the full resolution (0.7 arc-sec) of the 25 cm objective of the ORSO photoheliograph to be realized. First, filtergrams taken outside the core of Hα (Δλ≥ 0.9A) reveal the bright photospheric network (Vrabec, 1971; Dunn and Zirker, 1973; Dravins, 1974) which is, within the resolution capabilities of this instrument, co-spatial with strong magnetic fields near photospheric levels. In active regions the photospheric network is enhanced in brightness and becomes plainly visible as an aggregation of interlocking cells of various sizes. These data supplement magnetograms which are still needed to identify polarities and to furnish quantitative measurements of magnetic flux. Second, the visibility of the multi-threaded fine structure of filaments is usually much improved at wavelengths displaced from the centre of Hα. Thus a single instrument can provide the spatial data for investigating the relationship between the fine structure of filaments and highly localized concentrations of strong photospheric magnetic fields.

A Study of Active Regions in the Solar Corona Observed by OSO-I.

view Abstract Citations References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A Study of Active Regions in the Solar Corona Observed by OSO-I. Neupert, Werner M. Abstract The extreme ultraviolet solar spectrum, including emission lines from nine successive stages of ionization of iron, was observed by OSO-I from March through June 1962. Iron line emission from specific active regions existing on the sun during that interval has been estimated for successive solar rotations by comparing data acquired when only a single active region or a group of equivalent regions, appeared on the disk, to data taken in the absence of such regions. Fluxes at radio frequencies are analyzed in the same manner and are compared to the ultraviolet observations. The relative merits of the two types of measurements in determining coronal temperatures and densities is discussed. These data, combined with Ca+ plage observations and limb observations of coronal forbidden lines, are applied to a schematic coronal model to obtain physical conditions in the coronal region associated with a Type E sunspot group at various states in its development. Using the ionization equilibrium for iron calculated by Burgess and Seaton (Monthky Notices Roy. Astron. Soc. 127, 355, 1964), we infer an electron temperature of 4.2 x 106 0K and a density increase of approximately 10 times quiet coronal values at the time maximum development of the spot group. Under these conditions Fe XVI and Fe XVII represent the predominant stages of ionization of iron. Both temperature and density decrease as activity diminishes. For the region above the residual plage, after all spots have disappeared, we obtain 3 X 106 0K and a density of two or three times quiet coronal values. Additional properties of a model of the active region, including the aI~undance of iron. are discussed. Publication: The Astronomical Journal Pub Date: April 1966 DOI: 10.1086/109889 Bibcode: 1966AJ.....71..173N full text sources ADS |