[P-PS04] [EJ] New developments of planetary sciences with ALMA

[PPS04-P15] ALMA Discovery of Solar Umbral Brightening at λ=3 mm

*Kazumasa Iwai¹, Maria Loukitcheva^2,3,4, Masumi Shimojo⁵, Sami K Solanki^3,6, Stephen M White⁷ (1.National Institute of Information and Communications Technology, 2.New Jersey Institute of Technology, 3.Max Planck Institute for Solar System Research, 4.St. Petersburg University, 5.National Astronomical Observatory of Japan, 6.Kyung Hee University, 7.Air Force Research Laboratory)

Keywords:sunspots, Sun: chromosphere, Sun: radio radiation

We report the discovery of solar umbral brightening at a wavelength of 3 mm using the Atacama Large Millimeter/sub-millimeter Array (ALMA). Sunspots are 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, 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 spatially-resolved map including an entire sunspot at 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 umbral brightening. This enhanced emission corresponds to a temperature excess of 800 K relative to the surrounding inner penumbral region and coincides with excess brightening in the 1330 and 1400 Å slitjaw images of the Interface Region Imaging Spectrograph (IRIS), adjacent to a partial lightbridge. This λ=3 mm brightening may be an intrinsic feature of the sunspot umbra at chromospheric heights, or it could be related to a coronal plume since the brightening was coincident with the footpoint of a coronal loop observed at 171 Å. The λ=3 mm brightening is near a region of variable brightening observed at 1330 Å in part of the penumbra of the sunspot.