Temperature constraints from inversions of synthetic solar optical, UV, and radio spectra

Context. High-resolution observations of the solar chromosphere at millimeter wavelengths are now possible with the Atacama Large Millimeter Array (ALMA), bringing with them the promise of tackling many open problems in solar physics. Observations from other ground and space-based telescopes will greatly benefit from coordinated endeavors with ALMA, yet the diagnostic potential of combined optical, ultraviolet and mm observations has remained mostly unassessed. Aims. In this paper we investigate whether mm-wavelengths could aid current inversion schemes to retrieve a more accurate representation of the temperature structure of the solar atmosphere. Methods. We performed several non-LTE inversion experiments of the emergent spectra from a snapshot of 3D radiation-MHD simulation. We included common line diagnostics such as Ca II H, K, 8542 Å and Mg II h and k, taking into account partial frequency redistribution effects, along with the continuum around 1.2 mm and 3 mm. Results. We find that including the mm-continuum in inversions allows a more accurate inference of temperature as function of optical depth. The addition of ALMA bands to other diagnostics should improve the accuracy of the inferred chromospheric temperatures between log τ ∼ [−6, −4.5] where the Ca II and Mg II lines are weakly coupled to the local conditions. However, we find that simultaneous multiatom, non-LTE inversions of optical and UV lines present equally strong constraints in the lower chromosphere and thus are not greatly improved by the 1.2 mm band. Nonetheless, the 3 mm band is still needed to better constrain the mid-upper chromosphere.

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Modeling the quiet Sun cell and network emission with ALMA

Astronomy and Astrophysics ◽

10.1051/0004-6361/202038461 ◽

2020 ◽

Vol 640 ◽

pp. A57 ◽

Cited By ~ 1

Author(s):

C. E. Alissandrakis ◽

A. Nindos ◽

T. S. Bastian ◽

S. Patsourakos

Keyword(s):

Electron Temperature ◽

Brightness Temperature ◽

Absolute Calibration ◽

Solar Chromosphere ◽

Temperature Structure ◽

Cell Interior ◽

Network Cell ◽

Quiet Sun ◽

Millimeter Wavelengths ◽

Cell Segregation

Observations of the Sun at millimeter wavelengths with the Atacama Large Millimeter/submillimeter Array (ALMA) offer a unique opportunity to investigate the temperature structure of the solar chromosphere. In this article we expand our previous work on modeling the chromospheric temperature of the quiet Sun, by including measurements of the brightness temperature in the network and cell interiors, from high-resolution ALMA images at 3 mm (Band 3) and 1.26 mm (Band 6). We also examine the absolute calibration of ALMA full-disk images. We suggest that the brightness temperature at the center of the solar disk in Band 6 is ∼440 K above the value recommended by White et al. (2017, Sol. Phys., 292, 88). In addition, we give improved results for the electron temperature variation of the average quiet Sun with optical depth and the derived spectrum at the center of the disk. We found that the electron temperature in the network is considerably lower than predicted by model F of Fontenla et al. (1993, ApJ, 406, 319) and that of the cell interior considerably higher than predicted by model A. Depending on the network/cell segregation scheme, the electron temperature difference between network and cell at τ = 1 (100 GHz) ranges from ∼660 K to ∼1550 K, compared to ∼3280 K predicted by the models; similarly, the electron temperature, Te ratio ranges from ∼1.10 to 1.24, compared to ∼1.55 of the model prediction. We also found that the network/cell Te(τ) curves diverge as τ decreases, indicating an increase of contrast with height and possibly a steeper temperature rise in the network than in the cell interior.

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Chromosphere above sunspots as seen at millimeter wavelengths

Proceedings of the International Astronomical Union ◽

10.1017/s1743921311015651 ◽

2010 ◽

Vol 6 (S273) ◽

pp. 408-411

Author(s):

Maria A. Loukitcheva ◽

Sami K. Solanki ◽

Stephen M. White

Keyword(s):

Millimeter Wave ◽

Solar Chromosphere ◽

Temperature Structure ◽

Temperature Minimum ◽

Atmospheric Models ◽

Scientific Objective ◽

Successful Model ◽

Millimeter Wavelengths ◽

Deep Temperature ◽

Exact Temperature

AbstractMillimeter emission is known to be a sensitive diagnostic of temperature and density in the solar chromosphere. In this work we use millimeter wave data to distinguish between various atmospheric models of sunspots, whose temperature structure in the upper photosphere and chromosphere has been the source of some controversy. From mm brightness simulations we expect a radio umbra to change its appearance from dark to bright (compared to the Quiet Sun) at a given wavelength in the millimeter spectrum (depending on the exact temperature in the model used). Thereby the millimeter brightness observed above an umbra at several wavelengths imposes strong constraints on temperature and density stratification of the sunspot atmosphere, in particular on the location and depth of the temperature minimum and the location of the transition region. Current mm/submm observational data suggest that brightness observed at short wavelengths is unexpectedly low compared to the most widely used sunspot models such as of Maltby et al. (1986). A successful model that is in agreement with millimeter umbral brightness should have an extended and deep temperature minimum (below 3000 K), such as in the models of Severino et al. (1994). However, we are not able to resolve the umbra cleanly with the presently available observations and better resolution as well as better wavelength coverage are needed for accurate diagnostics of umbral brightness at millimeter wavelengths. This adds one more scientific objective for the Atacama Large Millimeter/Submillimeter Array (ALMA).

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Effects of Ambipolar Diffusion on Prominence Thread Models

International Astronomical Union Colloquium ◽

10.1017/s0252921100025513 ◽

1994 ◽

Vol 144 ◽

pp. 315-321 ◽

Cited By ~ 1

Author(s):

M. G. Rovira ◽

J. M. Fontenla ◽

J.-C. Vial ◽

P. Gouttebroze

Keyword(s):

Energy Balance ◽

Transition Region ◽

Ambipolar Diffusion ◽

Line Profiles ◽

Balance Equations ◽

Model Calculations ◽

Partial Frequency ◽

Frequency Redistribution ◽

Partial Frequency Redistribution ◽

Theoretical Structure

AbstractWe have improved previous model calculations of the prominence-corona transition region including the effect of the ambipolar diffusion in the statistical equilibrium and energy balance equations. We show its influence on the different parameters that characterize the resulting prominence theoretical structure. We take into account the effect of the partial frequency redistribution (PRD) in the line profiles and total intensities calculations.

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Frequency Redistribution Effects in the Formation of Lyman α in Prominences and Their Influence on the Ratio of Hα to Lα

International Astronomical Union Colloquium ◽

10.1017/s0252921100065210 ◽

1979 ◽

Vol 44 ◽

pp. 53-55

Author(s):

R.W. Milkey ◽

J.N. Heasley ◽

E.J. Schmahl ◽

O. Engvold

Keyword(s):

Line Profile ◽

Large Fraction ◽

Partial Frequency ◽

Frequency Redistribution ◽

Partial Frequency Redistribution ◽

Emergent Intensity

The effect of partial frequency redistribution in the formation of Lyman α in the chromosphere has been discussed by Milkey and Mihalas (1973) and others, and it has been shown that in this case the coherency of scattering in the wings of the line substantially influences the line profile. Although there are non-negligible sources for La photons within a prominence, a large fraction of the emergent line photons are due to scattering of photons incident on the surface of the prominence so that one expects that in a prominence the frequency redistribution processes will play an important role in determining the emergent intensity.

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