High-resolution millimeter-interferometer observations of the solar chromosphere

White, S. M.; Loukitcheva, M.; Solanki, S. K.

doi:10.1051/0004-6361:20052854

Cited by 55 publications

(69 citation statements)

References 51 publications

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“…The BIMA images were deconvolved using the maximum entropy method (MEM) and restored with a Gaussian beam of 12 (White et al 2006). Contemporaneous images of NOAA 10448 at 3 wavelengths are shown in Fig.…”

Section: Observational Data and Their Analysismentioning

confidence: 99%

The chromosphere above sunspots at millimeter wavelengths

Loukitcheva

Solanki

White

2014

A&A

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Aims. The aim of this paper is to demonstrate that millimeter wave data can be used to distinguish between various atmospheric models of sunspots, whose temperature structure in the upper photosphere and chromosphere has been the source of some controversy. Methods. We use observations of the temperature contrast (relative to the quiet Sun) above a sunspot umbra at 3.5 mm obtained with the Berkeley-Illinois-Maryland Array (BIMA), complemented by submm observations from Lindsey & Kopp (1995) and 2 cm observations with the Very Large Array. These are compared with the umbral contrast calculated from various atmospheric models of sunspots. Results. Current mm and submm observational data suggest that the brightness observed at these wavelengths is low compared to the most widely used sunspot models. These data impose strong constraints on the temperature and density stratifications of the sunspot umbral atmosphere, in particular on the location and depth of the temperature minimum and the location of the transition region. Conclusions. A successful model that is in agreement with millimeter umbral brightness should have an extended and deep temperature minimum (below 3000 K). Better spatial resolution as well as better wavelength coverage are needed for a more complete determination of the chromospheric temperature stratification above sunspot umbrae.

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Section: Observational Data and Their Analysismentioning

confidence: 99%

The chromosphere above sunspots at millimeter wavelengths

Loukitcheva

Solanki

White

2014

A&A

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“…6). Pixels in the lower left corner with very low mm brightness can result from the underestimation of the mm flux due to the high noise in the snapshot images (White et al 2006). Some of the peculiar pixels with intense mm brightness (in the upper left corner) are located above localized (small-scale) photospheric magnetic elements and near polarity changes.…”

Section: Relation Between Chromospheric Emission and Photospheric Magmentioning

confidence: 99%

The relationship between chromospheric emissions and magnetic field strength

Loukitcheva

Solanki

White

2009

A&A

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Aims. We analyze observational data from 4 instruments to study the correlations between chromospheric emission, spanning the heights from the temperature minimum region to the middle chromosphere, and photospheric magnetic field. Methods. The data consist of radio images at 3.5 mm from the Berkeley-Illinois-Maryland Array (BIMA), UV images at 1600 Å from TRACE, Ca ii K-line filtergrams from BBSO, and MDI/SOHO longitudinal photospheric magnetograms. For the first time interferometric millimeter data with the highest currently available resolution are included in such an analysis. We determine various parameters of the intensity maps and correlate the intensities with each other and with the magnetic field. Results. The chromospheric diagnostics studied here show a pronounced similarity in their brightness structures and map out the underlying photospheric magnetic field relatively well. We find a power law to be a good representation of the relationship between photospheric magnetic field and emission from chromospheric diagnostics at all wavelengths. The dependence of chromospheric brightness on magnetic field is found to be different for network and internetwork regions.

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“…Brightness temperature measurements of the quiet Sun were reviewed and compared with results of theoretical models by Gary (1996), by Loukitcheva et al (2004Loukitcheva et al ( , 2015, and by Benz (2009). Further, the quiet Sun emission in the wavelength range from λ = 0.85 mm to λ = 8 mm was measured by Bastian et al (1993b), White et al (2006), Brajša et al (2007a,b), and Iwai et al (2017). In the wavelength range 0.7 mm to 5 mm various measurements give the quiet Sun brightness temperature in the range from 5000 K to 8000 K, as summarized by White et al (2017).…”

Section: Introductionmentioning

confidence: 99%

First analysis of solar structures in 1.21 mm full-disc ALMA image of the Sun

Brajša

Sudar

Benz

et al. 2018

A&A

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Context. Various solar features can be seen in emission or absorption on maps of the Sun in the millimeter and submillimeter wavelength range. The recently installed Atacama Large Millimeter/submillimeter Array (ALMA) is capable of observing the Sun in that wavelength range with an unprecedented spatial, temporal and spectral resolution. To interpret solar observations with ALMA the first important step is to compare solar ALMA maps with simultaneous images of the Sun recorded in other spectral ranges. Aims. The first aim of the present work is to identify different structures in the solar atmosphere seen in the optical, infrared and EUV parts of the spectrum (quiet Sun, active regions, prominences on the disc, magnetic inversion lines, coronal holes and coronal bright points) in a full disc solar ALMA image. The second aim is to measure the intensities (brightness temperatures) of those structures and to compare them with the corresponding quiet Sun level. Methods. A full disc solar image at 1.21 mm obtained on December 18, 2015 during a CSV-EOC campaign with ALMA is calibrated and compared with full disc solar images from the same day in Hα line, in He I 1083 nm line core, and with various SDO images (AIA at 170 nm, 30.4 nm, 21.1 nm, 19.3 nm, and 17.1 nm and HMI magnetogram). The brightness temperatures of various structures are determined by averaging over corresponding regions of interest in the calibrated ALMA image. Results. Positions of the quiet Sun, active regions, prominences on the disc, magnetic inversion lines, coronal holes and coronal bright points are identified in the ALMA image. At the wavelength of 1.21 mm active regions appear as bright areas (but sunspots are dark), while prominences on the disc and coronal holes are not discernible from the quiet Sun background, although having slightly less intensity than surrounding quiet Sun regions. Magnetic inversion lines appear as large, elongated dark structures and coronal bright points correspond to ALMA bright points. Conclusions. These observational results are in general agreement with sparse earlier measurements at similar wavelengths. The identification of coronal bright points represents the most important new result. By comparing ALMA and other maps, it was found that the ALMA image was oriented properly and that the procedure of overlaying the ALMA image with other images is accurate at the 5 arc sec level. The potential of ALMA for physics of the solar chromosphere is emphasized.

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High-resolution millimeter-interferometer observations of the solar chromosphere

Cited by 55 publications

References 51 publications

The chromosphere above sunspots at millimeter wavelengths

The chromosphere above sunspots at millimeter wavelengths

The relationship between chromospheric emissions and magnetic field strength

First analysis of solar structures in 1.21 mm full-disc ALMA image of the Sun

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