ALMA Discovery of Solar Umbral Brightness Enhancement at λ = 3 mm
- Institute for Space-Earth Environmental Research, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, 464-8601 (Japan)
- Center for Solar-Terrestrial Research, New Jersey Institute of Technology, 323 Martin Luther King Boulevard, Newark, NJ 07102 (United States)
- Chile Observatory, National Astronomical Observatory of Japan, Mitaka, Tokyo 181-8588 (Japan)
- Max Planck Institute for Solar System Research, Justus-von-Liebig-Weg 3, D-37073 Göttingen (Germany)
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 view and 4.″9 × 2.″2 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 3 mm brightness temperature, which we call an umbral brightness enhancement. This enhanced emission corresponds to a temperature excess of 800 K relative to the surrounding inner penumbral region and coincides with excess brightness in the 1330 and 1400 Å slit-jaw images of the Interface Region Imaging Spectrograph ( IRIS ), adjacent to a partial lightbridge. This λ = 3 mm brightness enhancement may be an intrinsic feature of the sunspot umbra at chromospheric heights, such as a manifestation of umbral flashes, or it could be related to a coronal plume, since the brightness enhancement was coincident with the footpoint of a coronal loop observed at 171 Å.
- OSTI ID:
- 22654467
- Journal Information:
- Astrophysical Journal Letters, Vol. 841, Issue 2; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 2041-8205
- Country of Publication:
- United States
- Language:
- English
Similar Records
Formation and decay of rudimentary penumbra around a pore
OBSERVATIONS OF SUBARCSECOND BRIGHT DOTS IN THE TRANSITION REGION ABOVE SUNSPOTS WITH THE INTERFACE REGION IMAGING SPECTROGRAPH