ALMA Discovery of Solar Umbral Brightness Enhancement at {\lambda}=3 mm
Kazumasa Iwai, Maria Loukitcheva, Masumi Shimojo, Sami K. Solanki,, Stephen M. White

TL;DR
This study reports the first high-resolution ALMA observation revealing a brightness enhancement in the sunspot umbra at 3 mm, indicating complex thermal structures and potential links to chromospheric or coronal features.
Contribution
It presents the first high-resolution 3 mm ALMA map of a sunspot, discovering an umbral brightness enhancement and exploring its possible origins.
Findings
Detected a brightness temperature increase of 800 K in the umbra
Found the enhancement coincides with IRIS brightness excess
Suggested the feature may relate to chromospheric or coronal phenomena
Abstract
We report the discovery of a brightness enhancement in the center of a large sunspot umbra at a wavelength of 3 mm using the Atacama Large Millimeter/sub-millimeter Array (ALMA). Sunspots are amongst the most prominent features on the solar surface, but many of their aspects are surprisingly poorly understood. We analyzed a {\lambda}=3 mm (100 GHz) mosaic image obtained by ALMA, which includes a large sunspot within the active region AR12470 on December 16, 2015. The 3 mm map has a field-of-view and spatial resolution, which is the highest spatial-resolution map of an entire sunspot in this frequency range. We find a gradient of 3 mm brightness from a high value in the outer penumbra to a low value in the inner penumbra/outer umbra. Within the inner umbra, there is a marked increase in 3mm brightness temperature, which we call an umbral brightness enhancement. This enhanced emission…
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Taxonomy
TopicsSolar and Space Plasma Dynamics · Impact of Light on Environment and Health · Solar Radiation and Photovoltaics
