Solar Polar Brightening and Radius at 100 and 230GHz Observed by ALMA

Author(s):Show less -

Selhorst, Caius L. ^[1] ; Simoes, Paulo J. A. ^{[2, 3]} ; Brajsa, Roman ^[4] ; Valio, Adriana ^[3] ; Gimenez de Castro, C. G. ^{[5, 3]} ; Costa, Joaquim E. R. ^[6] ; Menezes, Fabian ^[3] ; Pierre Rozelot, Jean ^[7] ; Hales, Antonio S. ^{[8, 9]} ; Iwai, Kazumasa ^[10] ; White, Stephen ^[11]

Affiliation:Show less -

^[1] Univ Cruzeiro Sul, NAT, Sao Paulo, SP - Brazil

^[2] Univ Glasgow, SUPA Sch Phys & Astron, Glasgow G12 8QQ, Lanark - Scotland

^[3] Univ Presbiteriana Mackenzie, CRAAM, BR-01302907 Sao Paulo, SP - Brazil

^[4] Univ Zagreb, Fac Geodesy, Hvar Observ, Zagreb - Croatia

^[5] Univ Buenos Aires, CONICET, IAFE, Buenos Aires, DF - Argentina

^[6] CEA, Inst Nacl Pesquisas Espaciais, Sao Jose Dos Campos, SP - Brazil

^[7] Univ Cote dAzur, 77 Chemin Basses Moulieres, F-06130 Grasse - France

^[8] Joint ALMA Observ, Ave Alonso Cordova 3107, Santiago 7630355 - Chile

^[9] Natl Radio Astron Observ, 520 Edgemont Rd, Charlottesville, VA 22903 - USA

^[10] Nagoya Univ, Inst Space Earth Environm Res, Chikusa Ku, Furo Cho, Nagoya, Aichi 4648601 - Japan

^[11] Air Force Res Lab, Space Vehicles Div, Albuquerque, NM - USA

• Document type: Journal article
• Source: ASTROPHYSICAL JOURNAL; v. 871, n. 1 JAN 20 2019.
• Web of Science Citations: 2

Abstract

Polar brightening of the Sun at radio frequencies has been studied for almost 50 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 brightening emission for two semi-empirical atmospheric models, FAL-C and SSC. Both models presented larger limb intensities than the average 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. (AU)

• FAPESP's process: 14/10489-0 - Study of the changes in the solar magnetic field based on radio observations
• Grantee: Caius Lucius Selhorst
• Support Opportunities: Regular Research Grants