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A first look at the submillimeter Sun with ALMA View all abstracts by submitter

Costas Alissandrakis   Submitted: 2022-05-17 12:00

We present the first full-disk solar images obtained with the Atacama Large Millimeter/submillimeter Array (ALMA) in Band 7 (0.86 mm; 347 GHz). In spite of the low spatial resolution (21"), several interesting results were obtained. During our observation, the sun was practically devoid of active regions. Quiet Sun structures on the disk are similar to those in Atmospheric Imaging Assembly images at 1600 and 304 , after the latter are smoothed to the ALMA resolution, as noted previously for Band 6 (1.26 mm) and Band 3 (3 mm) images; they are also similar to negative Hα images of equivalent resolution. Polar coronal holes, which are clearly seen in the 304 band and small Hα filaments, are not detectable at 0.86 mm. We computed the center-to-limb variation of the brightness temperature, Tb, in Band 7, as well as in Bands 6 and 3, which were obtained during the same campaign, and we combined them to a unique curve of Tb(log μ_100), where μ_100 is the cosine of the heliocentric angle reduced to 100 GHz. Assuming that the absolute calibration of the Band 3 commissioning observations is accurate, we deduced a brightness temperature at the center of the disk of 6085 K for Band 7, instead of the value of 5500 K, extrapolated from the recommended values for Bands 3 and 6. More importantly, the Tb(log μ_100) curve flattens at large values of μ_100, and so does the corresponding Te(log τ_100) at large τ_100. This is probably an indication that we are approaching the temperature minimum.

Authors: C. E. Alissandrakis, T. S. Bastian, and A. Nindos
Projects: ALMA

Publication Status: Published in Astronomy & Astrophysics
Last Modified: 2022-05-17 12:33
Go to main E-Print page  Invited Review: Short-term Variability with the Observations from the Helioseismic and Magnetic Imager (HMI) Onboard the Solar Dynamics Observatory (SDO): Insights into Flare Magnetism  Data-driven modeling of solar coronal magnetic field evolution and eruptions  Edit Entry  Download Preprint  Delete Entry 

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