Solar prominence modelling and plasma diagnostics at ALMA wavelengths

Abstract

Our aim is to test potential solar prominence plasma diagnostics as obtained with the new solar capability of the Atacama Large Millimeter / submillimeter Array (ALMA). We investigate the thermal and plasma diagnostic potential of ALMA for solar prominences through the computation of brightness temperatures at ALMA wavelengths. The brightness temperature, for a chosen line of sight, is calculated using densities of hydrogen and helium obtained from a radiative transfer code under non local thermodynamic equilibrium (NLTE) conditions, as well as the input internal parameters of the prominence model in consideration. Two distinct sets of prominence models were used: isothermal-isobaric fine-structure threads, and large-scale structures with radially increasing temperature distributions representing the prominence-to-corona transition region. We compute brightness temperatures over the range of wavelengths in which ALMA is capable of observing (0.32 - 9.6mm), however we particularly focus on the bands available to solar observers in ALMA cycles 4 and 5, namely 2.6 - 3.6mm (Band 3) and 1.1 - 1.4mm (Band 6). We show how the computed brightness temperatures and optical thicknesses in our models vary with the plasma parameters (temperature and pressure) and the wavelength of observation. We then study how ALMA observables such as the ratio of brightness temperatures at two frequencies can be used to estimate the optical thickness and the emission measure for isothermal and non-isothermal prominences. From this study we conclude that, for both sets of models, ALMA presents a strong thermal diagnostic capability, provided that the interpretation of observations is supported by the use of non-LTE simulation results.

Submitted to Solar Physics

References in corpus (6)

• Solar science with the Atacama Large Millimeter/submillimeter Array - A new view of our Sun
• Observing the Sun with the Atacama Large Millimeter-submillimeter Array (ALMA): Fast-Scan Single-Dish Mapping
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• Millimeter radiation from a 3D model of the solar atmosphere I. Diagnosing chromospheric thermal structure
• Center-to-limb observations of the Sun with ALMA
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Cited by in corpus (5)

• First Spectral Analysis of a Solar Plasma Eruption Using ALMA
• First High Resolution Interferometric Observation of a Solar Prominence With ALMA
• ALMA as a prominence thermometer: First observations
• Spectral Gradient of the Thermal Millimetre Continuum as a Diagnostic for Optical Thickness in the Solar Atmosphere
• Combined Radio and Space-based Solar Observations: From Techniques to New Results