First solar observations with ALMA

Loukitcheva, M.

doi:10.1016/j.asr.2018.08.030

Cited by 18 publications

(18 citation statements)

References 22 publications

(20 reference statements)

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“…For a number of well-known reasons that we do not repeat in this work (see Loukitcheva 2019, for a review), the Atacama Large Millimeter/submillimeter Array (ALMA) is the ideal instrument for probing the solar chromosphere in the millimeterwave range. In a previous article (Alissandrakis et al 2017, hereafter Paper I), we inverted center-to-limb data for the average quiet Sun (QS) measured from full-disk (FD) ALMA images obtained during the commissioning period of December 2015 in Band 3 (100 GHz) and Band 6 (239 GHz), together with the observations of Bastian et al (1993) at 353 GHz, to compute the variation of the electron temperature, T e , as a function of the optical depth at 100 GHz, τ 100 .…”

Section: Introductionmentioning

confidence: 99%

Modeling the quiet Sun cell and network emission with ALMA

Alissandrakis

Nindos

Bastian

et al. 2020

A&A

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Observations of the Sun at millimeter wavelengths with the Atacama Large Millimeter/submillimeter Array (ALMA) offer a unique opportunity to investigate the temperature structure of the solar chromosphere. In this article we expand our previous work on modeling the chromospheric temperature of the quiet Sun, by including measurements of the brightness temperature in the network and cell interiors, from high-resolution ALMA images at 3 mm (Band 3) and 1.26 mm (Band 6). We also examine the absolute calibration of ALMA full-disk images. We suggest that the brightness temperature at the center of the solar disk in Band 6 is ∼440 K above the value recommended by White et al. (2017, Sol. Phys., 292, 88). In addition, we give improved results for the electron temperature variation of the average quiet Sun with optical depth and the derived spectrum at the center of the disk. We found that the electron temperature in the network is considerably lower than predicted by model F of Fontenla et al. (1993, ApJ, 406, 319) and that of the cell interior considerably higher than predicted by model A. Depending on the network/cell segregation scheme, the electron temperature difference between network and cell at τ = 1 (100 GHz) ranges from ∼660 K to ∼1550 K, compared to ∼3280 K predicted by the models; similarly, the electron temperature, Te ratio ranges from ∼1.10 to 1.24, compared to ∼1.55 of the model prediction. We also found that the network/cell Te(τ) curves diverge as τ decreases, indicating an increase of contrast with height and possibly a steeper temperature rise in the network than in the cell interior.

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Section: Introductionmentioning

confidence: 99%

Modeling the quiet Sun cell and network emission with ALMA

Alissandrakis

Nindos

Bastian

et al. 2020

A&A

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“…Extensive commissioning activities (see Shimojo et al 2017 andWhite et al 2017) addressed the peculiarities of solar observation with ALMA and culminated in observations obtained in December 2015. These data led to several publications, reviewed by Loukitcheva (2018). In those, there is only one presentation of a quiet Sun image at 1 mm close to the limb (Shimojo et al 2017).…”

Section: Introductionmentioning

confidence: 99%

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

Nindos

Alissandrakis

Bastian

et al. 2018

A&A

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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.

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“…The Sun emissivity has an expected average brightness temperature of 5000-100000 K within the ≈12 arcsec HPBW W-band radio beams of the SRT, with possible sporadic emission up to 10 6 K due to bright solar flares [48]- [49]. To avoid saturation of the second cryogenic LNA stage, the total RF power incoming into the receiver is reduced by ≈10 dB by quasi-optical RF solar filters (centered at 78 GHz and 110 GHz) with ≈6% relative bandwidth (bandwidth reduction from ≈60 GHz to ≈6 GHz).…”

Section: C) Receiver Looking At the Sun Through Solar Filtermentioning

confidence: 99%

Feasibility Study of a W-Band Multibeam Heterodyne Receiver for the Gregorian Focus of the Sardinia Radio Telescope

et al. 2022

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We report on the feasibility study of a W-band multibeam heterodyne receiver for the Sardinia Radio Telescope (SRT), a general purpose fully steerable 64-m diameter antenna located on the Sardinia island, Italy, managed by INAF ("Istituto Nazionale di Astrofisica," Italy). The W-band front-end is placed at the telescope Gregorian focal plane and will detect radio astronomy molecular spectral lines and broadband emission in the 3 mm atmospheric window. The goal specification of the receiver is a 4×4 focal plane array operating in dual-linear polarization with a front-end consisting of feed-horns placed in cascade with waveguide Orthomode Transducers (OMTs) and LNAs (Low Noise Amplifiers) cryogenically cooled at ≈20 K. The instantaneous FoV (Field of View) of the telescope is limited by the shaping of the 64-m primary and 7.9-m secondary mirrors. The cryogenic modules are designed to fit in the usable area of the focal plane and provide high-quality beam patterns with high antenna efficiency across the 70-116 GHz Radio Frequency (RF) band. The FoV covered by the 4×4 array is 2.15×2.15 arcmin 2 , unfilled, with separation between contiguous elements of 43 arcsec. Dual-sideband separation (2SB) down-conversion mixers are placed at the cryostat output and arranged in four four-pixel down-conversion modules with 4-12 GHz Intermediate Frequency (IF) bands (both Upper Side Band and Lower Side Band selectable for any pixel and polarization). The receiver utilizes a mechanical derotator to track the parallactic angle.

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First solar observations with ALMA

Cited by 18 publications

References 22 publications

Modeling the quiet Sun cell and network emission with ALMA

Modeling the quiet Sun cell and network emission with ALMA

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

Feasibility Study of a W-Band Multibeam Heterodyne Receiver for the Gregorian Focus of the Sardinia Radio Telescope

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