Letter to the Editor

First high-resolution look at the quiet Sun with ALMA at 3mm

¹ Physics Department, University of Ioannina, 45110, Ioannina, Greece
e-mail: anindos@cc.uoi.gr
² National Radio Astronomy Observatory, 520 Edgemont Road, VA, 22903 Charlottesville, USA
³ Lockheed Martin Solar and Astrophysics Laboratory, CA, 94304, Palo Alto, USA
⁴ Institute of Theoretical Astrophysics, University of Oslo, Blindern 0315, Oslo, PO Box 1029, Norway
⁵ Rosseland Centre for Solar Physics, University of Oslo, Blindern 0315, Oslo, PO Box 1029, Norway
⁶ Space Science Division, Naval Research Laboratory, Washington, DC, 20375, USA
⁷ Center for Astrophysics and Space Astronomy, University of Colorado, CO 80309, Boulder, USA
⁸ School of Physics and Astronomy, University of Glasgow, G12 8QQ, Glasgow, UK
⁹ Space Sciences Laboratory, University of California, 7 Gauss Way, CA, 94720-7450 Berkeley, USA
¹⁰ Japan Aerospace Exploration Agency, 3-1-1 Yoshinodai, Chuo-ku, Kanagawa, 252-5210, Sagamihara, Japan
¹¹ Institut d’Astrophysique Spatiale, UMR 8617, Université Paris 11, Orsay Cedex, 91405, France
¹² Big Bear Solar Observatory, New Jersey Institute of Technology, CA, 92314, Big Bear City, USA

Received: 21 August 2018
Accepted: 10 October 2018

Abstract

We present an overview of high-resolution quiet Sun observations, from disk center to the limb, obtained with the Atacama Large millimeter and sub-millimeter Array (ALMA) at 3 mm. Seven quiet-Sun regions were observed at a resolution of up to 2.5″ by 4.5″. We produced both average and snapshot images by self-calibrating the ALMA visibilities and combining the interferometric images with full-disk solar images. The images show well the chromospheric network, which, based on the unique segregation method we used, is brighter than the average over the fields of view of the observed regions by ∼305 K while the intranetwork is less bright by ∼280 K, with a slight decrease of the network/intranetwork contrast toward the limb. At 3 mm the network is very similar to the 1600 Å images, with somewhat larger size. We detect, for the first time, spicular structures, rising up to 15″ above the limb with a width down to the image resolution and brightness temperature of ∼1800 K above the local background. No trace of spicules, either in emission or absorption, is found on the disk. Our results highlight the potential of ALMA for the study of the quiet chromosphere.