The solar chromosphere at millimetre and ultraviolet wavelengths. I. Radiation temperatures and a detailed comparison

Abstract

Solar observations with the Atacama Large Millimeter/submillimeter Array (ALMA) provide us with direct measurements of the brightness temperature in the solar chromosphere. We study the temperature distributions obtained with ALMA Band 6 (in four sub-bands at 1.21, 1.22, 1.29, and 1.3 mm) for various areas at, and in the vicinity of, a sunspot, comprising quasi-quiet and active regions with different amounts of underlying magnetic fields. We compare these temperatures with those obtained at near- and far-ultraviolet (UV) wavelengths (and with the line-core intensities of the optically-thin far-UV spectra), co-observed with the Interface Region Imaging Spectrograph (IRIS) explorer. These include the emission peaks and cores of the Mg II k 279.6 nm and Mg II h 280.4 nm lines as well as the line cores of C II 133.4 nm, O I 135.6 nm, and Si IV 139.4 nm, sampling the mid-to-high chromosphere and the low transition region. Splitting the ALMA sub-bands resulted in an slight increase of spatial resolution in individual temperature maps, thus, resolving smaller-scale structures compared to those produced with the standard averaging routines. We find that the radiation temperatures have different, though somewhat overlapping, distributions in different wavelengths and in the various magnetic regions. Comparison of the ALMA temperatures with those of the UV diagnostics should, however, be interpreted with great caution, the former is formed under the local thermodynamic equilibrium (LTE) conditions, the latter under non-LTE. The mean radiation temperature of the ALMA Band 6 is similar to that extracted from the IRIS C II line in all areas with exception of the sunspot and pores where the C II poses higher radiation temperatures. In all magnetic regions, the Mg II lines associate with the lowest mean radiation temperatures in our sample. These will provide constraints for future numerical models.

arXiv commentAccepted for publication in the Astronomy & Astrophysics journal

References in corpus (36)

• The Interface Region Imaging Spectrograph (IRIS)
• The Atacama Large Millimeter/submillimeter Array
• The stellar atmosphere simulation code Bifrost
• Does a Non-Magnetic Solar Chromosphere Exist?
• VFISV: Very Fast Inversion of the Stokes Vector for the Helioseismic and Magnetic Imager
• Numerical simulation of the three-dimensional structure and dynamics of the non-magnetic solar chromosphere
• The formation of IRIS diagnostics II. The formation of the Mg II h&k lines in the solar atmosphere
• Ubiquitous torsional motions in type II spicules
• A publicly available simulation of an enhanced network region of the Sun
• Multiwavelength studies of MHD waves in the solar chromosphere: An overview of recent results
• The formation of IRIS diagnostics I. A quintessential model atom of Mg II and general formation properties of the Mg II h&k lines
• Solar science with the Atacama Large Millimeter/submillimeter Array - A new view of our Sun
• The formation of IRIS diagnostics. III. Near-ultraviolet Spectra and Images
• Physical Properties of a Sunspot Chromosphere with Umbral Flashes
• The Formation of IRIS diagnostics. IV. The Mg II triplet lines as a new diagnostic for lower chromospheric heating
• Observing the Sun with the Atacama Large Millimeter-submillimeter Array (ALMA): Fast-Scan Single-Dish Mapping
• Non-linear numerical simulations of magneto-acoustic wave propagation in small-scale flux tubes
• Dynamics of the Solar Magnetic Network. II. Heating the Magnetized Chromosphere
• Observing the Sun with Atacama Large Millimeter/submillimeter Array (ALMA): High Resolution Interferometric Imaging
• Hi-C & AIA observations of transverse MHD waves in active regions
• Transverse Oscillations in Slender Ca II H Fibrils Observed with Sunrise/SuFI
• Solar magnetoconvection and small-scale dynamo: Recent developments in observation and simulation
• The formation of IRIS diagnostics VI. The Diagnostic Potential of the C II Lines at 133.5 nm in the Solar Atmosphere
• High-frequency Oscillations in Small Magnetic Elements Observed with Sunrise/SuFI
• Heating of the magnetic chromosphere: observational constraints from Ca II 8542 spectra
• The Formation of IRIS Diagnostics. VII. The Formation of the OI 135.56 nm Line in the Solar Atmosphere
• A First Comparison of Millimeter Continuum and Mg II Ultraviolet Line Emission from the Solar Chromosphere
• Magnetic field variations associated with umbral flashes and penumbral waves
• A Hot Downflowing Model Atmosphere For Umbral Flashes And The Physical Properties Of Their Dark Fibrils
• Oscillations on width and intensity of slender Ca II H fibrils from Sunrise/SuFI
• Chromospheric backradiation in ultraviolet continua and Halpha
• Solar ALMA observations: constraining the chromosphere above sunspots
• Kinematics of Magnetic Bright Features in the Solar Photosphere
• Dynamics of the solar chromosphere. V. High-frequency modulation in ultraviolet image sequences from TRACE
• MOSiC: an analysis tool for IRIS spectral data
• ALMA Observations of the Sun in Cycle 4 and Beyond

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• The Sun at millimeter wavelengths V. Magnetohydrodynamic waves in a fibrillar structure