Solar polar brightening and radius at 100 and 230 GHz observed by ALMA

Selhorst, C. L. et al. (2019) Solar polar brightening and radius at 100 and 230 GHz observed by ALMA. Astrophysical Journal, 871(1), 45. (doi: 10.3847/1538-4357/aaf4f2)

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Abstract

Polar brightening of the Sun at radio frequencies has been studied for almost fifty years and yet a disagreement persists between solar atmospheric models and observations. Some observations reported brightening values much smaller than the expected values obtained from the models, with discrepancies being particularly large at millimeter wavelengths. New clues to calibrate the atmospheric models can be obtained with the advent of the Atacama Large Millimeter/submillimeter Array (ALMA) radio interferometer. In this work, we analyzed the lower limit of the polar brightening observed at 100 and 230 GHz by ALMA, during its Science Verification period, 2015 December 16-20. We find that the average polar intensity is higher than the disk intensity at 100 and 230 GHz, with larger brightness intensities at the South pole in eight of the nine maps analyzed. The observational results were compared with calculations of the millimetric limb brightnening emission for two semi-empirical atmospheric models, FAL- C (Fontenla et al. 1993) and SSC (Selhorst et al. 2005a). Both models presented larger limb intensities than the averaged observed values. The intensities obtained with the SSC model were closer to the observations, with polar brightenings of 10.5% and 17.8% at 100 and 230 GHz, respectively. This discrepancy may be due to the presence of chromospheric features (like spicules) at regions close to the limb.

Item Type:Articles
Additional Information:C.L.S. acknowledges financial support from the São Paulo Research Foundation (FAPESP), grant number 2014/ 10489-0. P.J.A.S. acknowledges support from the University of Glasgow’s Lord Kelvin Adam Smith Leadership Fellowship. A.V. and F.M. acknowledge partial funding from Fapesp. R.B. acknowledges partial support by Croatian Science Foundation under the project 6212 “Solar and Stellar Variability”.
Status:Published
Refereed:Yes
Glasgow Author(s) Enlighten ID:Simoes, Dr Paulo
Authors: Selhorst, C. L., Simoes, P. J.A., Brajša, R., Valio, A., Giménez de Castro, C.G., Costa, J. E.R., Menezes, F., Rozelot, J. P., Hales, A. S., Iwai, K., and White, S.
College/School:College of Science and Engineering > School of Physics and Astronomy
Journal Name:Astrophysical Journal
Publisher:American Astronomical Society
ISSN:0004-637X
ISSN (Online):1538-4357
Copyright Holders:Copyright © 2019 American Astronomical Society
First Published:First published in Astrophysical Journal 871(1):45
Publisher Policy:Reproduced in accordance with the copyright policy of the publisher
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