An Interpretation of the Coronal Holes’ Visibility in the Millimeter Wavelength Range
| Autor: | Rajka Jurdana-Šepić, Manuela Temmer, Roman Brajša, B. Šaina, Arnold O. Benz, Hubertus Wöhl |
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| Rok vydání: | 2007 |
| Předmět: |
Physics
business.industry Astrophysics::High Energy Astrophysical Phenomena Bremsstrahlung Coronal hole Astronomy and Astrophysics Astrophysics Coronal loop Corona Wavelength Optics Space and Planetary Science Brightness temperature Physics::Space Physics Astrophysics::Solar and Stellar Astrophysics Millimeter business Chromosphere |
| Zdroj: | Solar Physics. 245:167-176 |
| ISSN: | 1573-093X 0038-0938 |
| DOI: | 10.1007/s11207-007-9008-4 |
| Popis: | Various observations indicate that coronal holes generally appear as low brightness temperature regions (LTRs) in the centimeter and millimeter wavelength ranges. However, within their borders local enhancements of radiation, that is, high brightness temperature regions (HTRs), often occur. The theory behind the described behavior is not fully understood and therefore we analyze full-disk solar images obtained at a wavelength of 8 mm at Metsahovi Radio Observatory and compare them with data simultaneously taken in other wavelength ranges. The observational finding that the average brightness temperature of coronal holes is not much different from the quiet-Sun level (with localized deviations toward higher and lower intensities on the order of a few percent) is compared with theoretical models of the thermal bremsstrahlung radiation originating in the solar chromosphere, transition region, and corona. Special attention is devoted to the interpretation of the localized enhancements of radiation observed inside coronal holes at millimeter wavelengths. The main conclusion is that the most important contribution to the brightness temperature comes from an increased density in the transition region and low corona (i.e., at the heights where the temperature is below 106 K). This can explain both the LTRs and HTRs associated with coronal holes. |
| Databáze: | OpenAIRE |
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