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Modeling of the Brightness of the Chromospheric Network Based on ALMA High Resolution Observations of the Quiet Sun

Published onJun 01, 2020
Modeling of the Brightness of the Chromospheric Network Based on ALMA High Resolution Observations of the Quiet Sun

ALMA observations of the Sun at mm-λ offer a unique opportunity to investigate the temperature/density structure of the solar chromosphere. In a previous work (Alissandrakis et al 2017, A&A 605, A78) we measured the center-to-limb variation of the brightness temperature, Tb, using low resolution ALMA full-disk observations in Band 3 (3mm) and Band 6 (1.26 mm), together with data at 0.85 mm from Bastian et al. 1993 (ApJ, 415, 364). Combining all data and inverting the solution of the transfer equation we found that the electron temperature, Te, in the range of 0.34 < τ100 < 12, where τ100 is the optical depth at 100 GHz, was ~5% (~300 K) below the one predicted by model C (average quiet sun) of FAL93 (Fontenla, Avrett, & Loeser, 1993, ApJ, 406, 319). Here we expand that work by including measurements of the brightness temperature in the network and cell interiors, from high resolution ALMA images in Bands 3 and 6. We found that the observed Tb in the network is considerably lower than predicted by the FAL93 model F and that of the cell interior considerably higher than predicted by the FAL93 model A. The observed network/cell difference of brightness temperature at the center of the disk, at 100 GHz is about 920 K, compared to ~3250 K predicted by the FAL93 models; similarly, the Tb, ratio is ~1.14, against ~1.51 of the model prediction. After inversion of the observed data, the electron temperature of cell interior at τ100=1 is ~390 K below the average (~600 K above model A) and of the network ~400 K above the average (~1800 K below model A). The implications of these results will be discussed. We will also discuss the question of the normalization of brightness temperature observed by ALMA.

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