• DOI:10.1051/0004-6361/202243774
• Corpus ID: 248496917

A first look at the submillimeter Sun with ALMA

@article{Alissandrakis2022AFL,
  title={A first look at the submillimeter Sun with ALMA},
  author={C. E. Alissandrakis and Timothy S. Bastian and Alexander Nindos},
  journal={Astronomy \& Astrophysics},
  year={2022}
}

• C. Alissandrakis, T. Bastian, A. Nindos
• Published 2 May 2022
• Physics
• Astronomy & Astrophysics

We present the first full-disk solar images obtained with the Atacama Large Millimeter / submillimeter Array (ALMA) in Band 7 (0.86mm; 347GHz). In spite of the low spatial resolution (21 (cid:48)(cid:48) ), 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 1600Å and 304Å, after the latter are smoothed to the ALMA resolution, as noted previously for Band 6 (1.26mm) and Band 3 (3mm) images; they are also similar to negative H α images of equivalent resolution. Polar coronal holes, which are clearly seen in the 304Å band and small H α filaments, are not detectable at 0.86mm. We computed the center-to-limb variation of the brightness temperature, T b , 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 T b (log µ 100 ), where µ 100 is the cosine of the heliocentric angle reduced to 100GHz. 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 6085K for Band 7, instead of the value of 5500K, extrapolated from the recommended values for Bands 3 and 6. More importantly, the T b (log µ 100 ) curve flattens at large values of µ 100 , and so does the corresponding T e (log τ 100 ) at large τ 100 . This is probably an indication that we are approaching the temperature minimum.