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Solar ALMA observations: constraining the chromosphere above sunspots by M. Loukitcheva et al.*

20 Feb 2018, 10:02 UTC
Solar ALMA observations: constraining the chromosphere above sunspots  by M. Loukitcheva et al.*
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Our understanding of sunspots is far from complete despite intensive research over hundreds of years. Radiation at submillimeter and millimeter wavelengths is formed in local thermodynamic equilibrium (LTE) in the low to mid chromosphere, and its intensity depends linearly on the ambient temperature of the medium. Observations at these wavelengths thus provide important diagnostics of sunspot chromospheres (Loukitcheva et al. 2014). The largest radio telescope in the world, the Atacama Large Millimeter/Submillimeter Array (ALMA), which started scientific solar observations in 2016, provides high-resolution observations at mm wavelengths that can resolve and isolate structures within a sunspot (umbra and penumbra), allowing us to test models for the chromospheres of such features. Using ALMA Science Verification data from 2015, we compare ALMA observations of a sunspot at two mm wavelengths with the predictions of sunspot umbral and penumbral models.
ALMA observations and data analysis
The ALMA observations were carried out on 2015-12-16 at 100 GHz (corresponding to a wavelength of 3mm), and on 2015-12-18-12 at 230 GHz (1.3 mm). The images were synthesized from interferometric mosaic observations with beam sizes of 4.9′′x2.2′′ and 2.4′′x0.9′′ at 3 mm and 1.3 mm, respectively, and cover a field-of-view (FOV) of 300′′x300′′ at 3 mm ...

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