A First Comparison of Millimeter Continuum and Mg ii Ultraviolet Line Emission from the Solar Chromosphere

Bastian, T. S.; Chintzoglou, Georgios; Pontieu, Bart De; Shimojo, Masataka; Schmit, D. J.; Leenaarts, J.; Loukitcheva, M.

doi:10.3847/2041-8213/aa844c

Cited by 41 publications

(49 citation statements)

References 20 publications

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“…The small size of the FOV and thus the peculiarities of the observed regions will produce variations in the statistical properties derived from different observations. These results should be compared to a corresponding analysis of mosaicking data that cover larger FOVs (see e.g., Bastian et al 2017;Jafarzadeh et al 2019). Furthermore, the test for different angular resolutions implies that more extended array configurations of ALMA, which might be offered in future observing cycles, are likely to lead to higher rms variations and thus more contrast in the reconstructed images.…”

Section: Dependence On Angular Resolutionmentioning

confidence: 99%

“…While the first regular ALMA observations of the Sun were only offered in Cycle 4 with a first solar campaign in December 2016, earlier observations from Commissioning and Science Verification (CSV) campaigns have been made publicly available. Both regular and CSV data are already used in publications: Alissandrakis et al (2017), Bastian et al (2017), Shimojo et al (2017b), Brajša et al (2018), Nindos et al (2018), Yokoyama et al (2018), Jafarzadeh et al (2019), Loukitcheva et al (2019), Molnar et al (2019), Rodger et al (2019), Selhorst et al (2019), Patsourakos et al (2020), da Silva Santos et al (2020.…”

Section: Introductionmentioning

confidence: 99%

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The Sun at millimeter wavelengths

Wedemeyer

Szydlarski

Jafarzadeh

et al. 2020

A&A

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Context. The Atacama Large Millimeter/submillimeter Array (ALMA) started regular observations of the Sun in 2016, first offering receiver Band 3 at wavelengths near 3 mm (100 GHz) and Band 6 at wavelengths around 1.25 mm (239 GHz). Aims. Here we present an initial study of one of the first ALMA Band 3 observations of the Sun. Our aim is to characterise the diagnostic potential of brightness temperatures measured with ALMA on the Sun. Methods. The observation covers a duration of 48 min at a cadence of 2 s targeting a quiet Sun region at disc-centre. Corresponding time series of brightness temperature maps are constructed with the first version of the Solar ALMA Pipeline and compared to simultaneous observations with the Solar Dynamics Observatory (SDO). Results. The angular resolution of the observations is set by the synthesised beam, an elliptical Gaussian that is approximately 1.4″ × 2.1″ in size. The ALMA maps exhibit network patches, internetwork regions, and elongated thin features that are connected to large-scale magnetic loops, as confirmed by a comparison with SDO maps. The ALMA Band 3 maps correlate best with the SDO/AIA 171 Å, 131 Å, and 304 Å channels in that they exhibit network features and, although very weak in the ALMA maps, imprints of large-scale loops. A group of compact magnetic loops is very clearly visible in ALMA Band 3. The brightness temperatures in the loop tops reach values of about 8000−9000 K and in extreme moments up to 10 000 K. Conclusions. ALMA Band 3 interferometric observations from early observing cycles already reveal temperature differences in the solar chromosphere. The weak imprint of magnetic loops and the correlation with the 171, 131, and 304 SDO channels suggests, however, that the radiation mapped in ALMA Band 3 might have contributions from a wider range of atmospheric heights than previously assumed, but the exact formation height of Band 3 needs to be investigated in more detail. The absolute brightness temperature scale as set by total power measurements remains less certain and must be improved in the future. Despite these complications and the limited angular resolution, ALMA Band 3 observations have a large potential for quantitative studies of the small-scale structure and dynamics of the solar chromosphere.

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Section: Dependence On Angular Resolutionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

The Sun at millimeter wavelengths

Wedemeyer

Szydlarski

Jafarzadeh

et al. 2020

A&A

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“…The first high-resolution images of the quiet Sun in the millimeter range were obtained by White et al (2006) and Loukitcheva et al (2006) who used the Berkeley-Illinois-Maryland Association Array (BIMA) to obtain ∼ 10 ′′ resolution. With the advent of ALMA a new generation of high-resolution millimeterwavelength images has been forming (e.g., Bastian et al, 2017;Shimojo et al, 2017a,b;Nindos et al, 2018;Yokoyama et al, 2018;Jafarzadeh et al, 2019;Loukitcheva et al, 2019;Molnar et al, 2019;Patsourakos et al, 2020;Wedemeyer et al, 2020) and an example is presented in Figure 2. The figure indicates that the chromospheric network, delineated in the AIA 1,600 Å image, is the dominant structure in the radio images.…”

Section: Imaging Observations Of the Non-flaring Sunmentioning

confidence: 99%

Incoherent Solar Radio Emission

Nindos

2020

Front. Astron. Space Sci.

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Incoherent solar radio radiation comes from the free-free, gyroresonance, and gyrosynchrotron emission mechanisms. Free-free is primarily produced from Coulomb collisions between thermal electrons and ions. Gyroresonance and gyrosynchrotron result from the acceleration of low-energy electrons and mildly relativistic electrons, respectively, in the presence of a magnetic field. In the non-flaring Sun, free-free is the dominant emission mechanism with the exception of regions of strong magnetic fields which emit gyroresonance at microwaves. Due to its ubiquitous presence, free-free emission can be used to probe the non-flaring solar atmosphere above temperature minimum. Gyroresonance opacity depends strongly on the magnetic field strength and orientation; hence it provides a unique tool for the estimation of coronal magnetic fields. Gyrosynchrotron is the primary emission mechanism in flares at frequencies higher than 1-2 GHz and depends on the properties of both the magnetic field and the accelerated electrons, as well as the properties of the ambient plasma. In this paper we discuss in detail the above mechanisms and their diagnostic potential.

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“…By comparing ALMA brightness with full-disk solar images in Hα line, in He I 1083 nm line core, with the AIA/SDO images at 170 nm, 30.4 nm, 21.1 nm, 19.3 nm, and 17.1 nm, and HMI/SDO magnetograms, the authors identified and described the mm-λ brightness structures related to the quiet Sun, active regions, prominences on the disk, magnetic inversion lines, coronal holes and coronal bright points. Bastian et al (2017) compared ALMA observations of the 1.25 mm-λ continuum emission from the solar active region AR 12470 on 2015 December 18 with nearly simultaneous observations of the Mg II line intensities from the Interface Region Imaging Spectrograph (IRIS), which are believed to form at similar heights in the chromosphere (Figire 4). Apart from the clear similarities between the emisions at the two wavelengths, distinct differences between the mm brightness temperature and the UV radiation temperature were found, including a compressed range of radiation temperatures of Mg II lines as compared to the brightness temperatures at 1.25 mm and an offset between the temperatures at two wavelengths.…”

Section: First Solar Alma Sciencementioning

confidence: 99%

“…(c) the contours of the 1.25 mm brightness overlaid on the IRIS radiation temperature map background. FromBastian et al (2017). c AAS.…”

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confidence: 99%

First solar observations with ALMA

Loukitcheva

2019

Advances in Space Research

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The Atacama Large Millimeter-Submillimeter Array (ALMA) has opened a new window for studying the Sun via high-resolution high-sensitivity imaging at millimeter wavelengths. In this contribution I review the capabilities of the instrument for solar observing and describe the extensive effort taken to bring the possibility of solar observing with ALMA to the scientific community. The first solar ALMA observations were carried out during 2014 and 2015 in two ALMA bands, Band 3 (λ = 3 mm) and Band 6 (λ = 1.3 mm), in single-dish and interferometric modes, using single pointing and mosaicing observing techniques, with spatial resolution up to ∼2 and ∼1 in the two bands, respectively. I overview several recently published studies which made use of the first solar ALMA observations, describe current status of solar observing with ALMA and briefly discuss the future capabilities of the instrument.

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A First Comparison of Millimeter Continuum and Mg ii Ultraviolet Line Emission from the Solar Chromosphere

Cited by 41 publications

References 20 publications

The Sun at millimeter wavelengths

The Sun at millimeter wavelengths

Incoherent Solar Radio Emission

First solar observations with ALMA

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