ALMA Discovery of Solar Umbral Brightness Enhancement at λ = 3 mm

  title={ALMA Discovery of Solar Umbral Brightness Enhancement at $\lambda$ = 3 mm},
  author={Kazumasa Iwai and Maria A. Loukitcheva and Masumi Shimojo and Sami K. Solanki and Stephen M. White},
  journal={The Astrophysical Journal Letters},
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 among the most prominent features on the solar surface, but many of their aspects are surprisingly poorly understood. We analyzed a λ = 3 mm (100 GHz) mosaic image obtained by ALMA that includes a large sunspot within the active region AR12470, on 2015 December 16. The 3 mm map has a 300″ × 300″ field of… 

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