Observation of Chromospheric Sunspot at Millimeter Range with the Nobeyama 45 m Telescope

Abstract

The brightness temperature of the radio free-free emission at millimeter range is an effective tool for characterizing the vertical structure of the solar chromosphere. In this paper, we report on the first single-dish observation of a sunspot at 85 and 115 GHz with sufficient spatial resolution for resolving the sunspot umbra using the Nobeyama 45 m telescope. We used radio attenuation material, i.e. a solar filter, to prevent the saturation of the receivers. Considering the contamination from the plage by the side-lobes, we found that the brightness temperature of the umbra should be lower than that of the quiet region. This result is inconsistent with the preexisting atmospheric models. We also found that the brightness temperature distribution at millimeter range strongly corresponds to the ultraviolet (UV) continuum emission at 1700 Å, especially at the quiet region.

arXiv comment15 pages, 5 figures, accepted for publication in ApJ

References in corpus (2)

• Inter-network regions of the Sun at millimetre wavelengths
• The chromosphere above sunspots at millimeter wavelengths

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• Chromospheric sunspots in the millimeter range as observed by the Nobeyama Radioheliograph
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• A Genetic Algorithm to model Solar Radio Active Regions from 3D Magnetic Field Extrapolations
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• The Chromospheric Solar Limb Brightening at Radio, Millimeter, Sub-millimeter, and Infrared Wavelengths
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