THE FORMATION OF THE Hα LINE IN THE SOLAR CHROMOSPHERE

By J. Leenaarts, M. Carlsson, L. R. V. Voort. 2012

176 citations recorded by the source corpus.

We use state-of-the-art radiation-MHD simulations and three-dimensional (3D) non-LTE radiative transfer computations to investigate Hα line formation in the solar chromosphere and apply the results of this investigation to develop the potential of Hα as a diagnostic of the chromosphere. We show that one can accurately model Hα line formation assuming statistical equilibrium and complete frequency redistribution provided the computation of the model atmosphere included non-equilibrium ionization of hydrogen and the Lyα and Lyβ line profiles are described by Doppler profiles. We find that 3D radiative transfer is essential in modeling hydrogen lines due to the low photon destruction probability in Hα. The Hα opacity in the upper chromosphere is mainly sensitive to the mass density and only weakly sensitive to the temperature. We find that the Hα line-core intensity is correlated with the average formation height: The larger the average formation height is, the lower the intensity will be. The line-core width is a measure of the gas temperature in the line-forming region. The fibril-like dark structures seen in Hα line-core images computed from our model atmosphere are tracing magnetic field lines. These structures are caused by field-aligned ridges of enhanced chromospheric mass density that raise their average formation height, and therefore make them appear dark against their deeper-formed surroundings. We compare with observations, and find that the simulated line-core widths are very similar to the observed ones, without the need for additional microturbulence.

Subfields: Artificial Intelligence, Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/a6e37021effdb397b0582af986a5bfe91335fbbc

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Citations in the corpus

THE FORMATION OF IRIS DIAGNOSTICS. II. THE FORMATION OF THE Mg ii h&k LINES IN THE SOLAR ATMOSPHERE (2013, methodology): “The same mechanism acts in the Hα line core, as explained by Leenaarts et al.(2012).”
A publicly available simulation of an enhanced network region of the Sun (2015, methodology): “The formation of the H-α line was studied in Leenaarts et al. (2012), the Hanlé effect of Ly-α was studied by Štěpán et al. (2012, 2015) and the signatures of heating of the magnetic chromosphere were treated by de la Cruz Rodrı́guez et al. (2013).”
Solar Fine-Scale Structures. I. Spicules and Other Small-Scale, Jet-Like Events at the Chromospheric Level: Observations and Physical Parameters (2012, methodology): “Leenaarts et al. (2006) showed the potential of these Hα bright points as proxies of the magnetic elements.”
Multiwavelength Studies of MHD Waves in the Solar Chromosphere (2015, background): “…as uncertainties in the multi-level atomic transitions, atmospheric mixing-lengths, non-gray radiative transfer components and sensitivities to asymmetric spectral line profiles (Cuntz et al. 2007; Caffau et al. 2011; Beeck et al. 2012; Leenaarts et al. 2012; Prakapavičius et al. 2013).”