Solar Prominence Modelling and Plasma Diagnostics at ALMA Wavelengths

Rodger, A. S.; Labrosse, Nicolas

doi:10.1007/s11207-017-1161-9

Cited by 14 publications

(19 citation statements)

References 27 publications

(34 reference statements)

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“…The quiet solar chromosphere emits mm/sub-mm radiation, in the Rayleigh-Jeans limit, predominantly through thermal bremsstrahlung which is a local thermodynamic equilibrium (LTE) emission mechanism. Therefore, a brightness temperature measurement from optically thick source material will be highly representative of the electron temperature of the region in which the emission was formed (Wedemeyer et al 2016;Rodger & Labrosse 2017). Until ALMA however, mm/sub-mm imaging has lacked sufficiently high resolution to allow for in-depth analysis at the small scales critical for understanding many solar atmospheric processes.…”

Section: Introductionmentioning

confidence: 99%

First Spectral Analysis of a Solar Plasma Eruption Using ALMA

Rodger

Labrosse

Wedemeyer

et al. 2019

ApJ

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The aim of this study is to demonstrate how the logarithmic millimeter continuum gradient observed using the Atacama Large Millimeter/submillimeter Array (ALMA) may be used to estimate optical thickness in the solar atmosphere. We discuss how using multi-wavelength millimeter measurements can refine plasma analysis through knowledge of the absorption mechanisms. Here we use sub-band observations from the publicly available science verification (SV) data, whilst our methodology will also be applicable to regular ALMA data. The spectral resolving capacity of ALMA SV data is tested using the enhancement coincident with an X-ray Bright Point (XBP) and from a plasmoid ejection event near active region NOAA12470 observed in Band 3 (84-116 GHz) on 17/12/2015. We compute the interferometric brightness temperature light-curve for both features at each of the four constituent sub-bands to find the logarithmic millimetre spectrum. We compared the observed logarithmic spectral gradient with the derived relationship with optical thickness for an isothermal plasma to estimate the structure's optical thicknesses. We conclude, within 90% confidence, that the stationary enhancement has an optical thickness between 0.02 ≤ τ ≤ 2.78, and that the moving enhancement has 0.11 ≤ τ ≤ 2.78, thus both lie near to the transition between optically thin and thick plasma at 100 GHz. From these estimates, isothermal plasmas with typical Band 3 background brightness temperatures would be expected to have electron temperatures of ∼7370 -15300 K for the stationary enhancement and between ∼7440 -9560 K for the moving enhancement, thus demonstrating the benefit of sub-band ALMA spectral analysis.

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Section: Introductionmentioning

confidence: 99%

First Spectral Analysis of a Solar Plasma Eruption Using ALMA

Rodger

Labrosse

Wedemeyer

et al. 2019

ApJ

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“…To interpret the behaviour of the Mg II chromospheric lines a NLTE (i.e. departures from LTE) radiative transfer approach is necessary (Heinzel et al 2014(Heinzel et al , 2015Rodger & Labrosse 2017).…”

Section: Introductionmentioning

confidence: 99%

On the Dynamic Nature of a Quiescent Prominence Observed by IRIS and MSDP Spectrographs

Ruan

Schmieder

Mein

et al. 2018

ApJ

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Quiescent solar prominences are generally considered to have a stable large-scale structure. However, they consist of multiple small-scale structures that are often significantly dynamic. To understand the nature of prominence plasma dynamics we use the high spatial, temporal, and spectral resolution observations obtained by Interface Region Imaging Spectrograph (IRIS) during a coordinated campaign with the Multichannel Subtractive Double Pass spectrograph at the Meudon Solar Tower. Detailed analysis of the IRIS observations of Mg ii lines, including the analysis of Dopplershift and line width obtained with two different methods (quantile method and Gaussian-fit method) are discussed in the frame of the dynamic nature of the structures. Large-scale coherent blueshift and redshift features are observed in Mg ii lines and Hα exhibiting a slow evolution during 1:40 hr of observations. We explain the presence of several significantly asymmetric peaks in the observed Mg ii line profiles by the presence of several prominence fine structures moving with different velocities located along the line of sight (LOS). In such a case, the decrease of the intensity of individual components of the observed spectra with the distance from the central wavelength can be explained by the Doppler dimming effect. We show that C ii line profiles may be used to confirm the existence of multi-components along the LOS.

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“…We then calculate the brightness temperature for a set of horizontal lines-of-sight through the prominence cylinder. We follow the same methods for brightness temperature calculation as outlined in Rodger & Labrosse (2017) with one notable change in the calculation of the thermal gaunt factor. In this study we no longer estimate the thermal gaunt factor through the assumption given in Dulk (1985) for plasma of temperature < 2 × 10 5 K, but instead take our values by interpolating the table of calculated thermal gaunt factors of van Hoof et al (2014), as described in Gayet (1970); Simões et al (2017).…”

Section: Modellingmentioning

confidence: 99%

Spectral gradient of the thermal millimetre continuum as a diagnostic for optical thickness in the solar atmosphere

Rodger

Labrosse

2018

A&A

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Aims. In this article we aim to show how the gradient of the thermal millimetre continuum spectrum, as emitted from the quiet solar atmosphere, may be used as a diagnostic for the optical thickness regime at the centre of the observing frequency band. Methods. We show the theoretical derivation of the gradient of the millimetre continuum for both logarithmic-and linear-scale spectra. We compare this expression with the empirical relationship between the slope of the millimetre continuum spectrum and the plasma optical thickness computed from both isothermal and multi-thermal two-dimensional cylindrical radiative transfer models. Results. It is found that the logarithmic-scale spectral gradient provides a clear diagnostic for the optical thickness regime for both isothermal and multi-thermal plasmas, provided that a suitable correction is made for a non-constant gaunt factor over the frequency band. For the use of observers we present values for this correction at all ALMA bands and at a wide range of electron temperatures. Conclusions. We find that the spectral gradient can be used to find (a) whether the source is fully optically thin, (b) the optical thickness of the source if it lies within the transitional regime between optically thin and thick plasma (τ ≈ 10 −1 − 10 1 ), or (c) whether the source is fully optically thick for an isothermal plasma. A multi-thermal plasma will act the same as an isothermal plasma for case (a), however, the transitional regime will only extend from τ ≈ 10 −1 − 10 0 . Above τ = 1 the slope of the continuum will depend increasingly on the temperature gradient, as well as the optical thickness, reducing the reliability of the diagnostic.

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Solar Prominence Modelling and Plasma Diagnostics at ALMA Wavelengths

Cited by 14 publications

References 27 publications

First Spectral Analysis of a Solar Plasma Eruption Using ALMA

First Spectral Analysis of a Solar Plasma Eruption Using ALMA

On the Dynamic Nature of a Quiescent Prominence Observed by IRIS and MSDP Spectrographs

Spectral gradient of the thermal millimetre continuum as a diagnostic for optical thickness in the solar atmosphere

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