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.

15 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

Cited by in corpus (8)

• Observing the Sun with the Atacama Large Millimeter-submillimeter Array (ALMA): Fast-Scan Single-Dish Mapping
• Center-to-limb observations of the Sun with ALMA
• Solar ALMA observations: constraining the chromosphere above sunspots
• The Brightness Temperature of the Quiet Solar Chromosphere at 2.6 mm
• ALMA Discovery of Solar Umbral Brightness Enhancement at λ=3 mm
• A Genetic Algorithm to model Solar Radio Active Regions from 3D Magnetic Field Extrapolations
• Detection of emission in the Si i 1082.7 nm line core in sunspot umbrae
• Modeling brightness temperature of sunspots using ALMA single-dish observations