Resonance-Line Transfer with Partial Redistribution: a Preliminary Study of Lyman a in the Solar Chromosphere

Milkey, R. W.; Mihalas, Dimitri

doi:10.1086/152448

Cited by 63 publications

(25 citation statements)

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“…Complete frequency re-distribution was assumed for all transitions except the Lyman transitions, for which the effects of partial re-distribution are mimicked by truncating the line profiles at ten Doppler widths (Milkey & Mihalas 1973). The equations are solved using five angle points and up to 100 frequency A72, page 4 of 12 points for each transition.…”

Section: Modelmentioning

confidence: 99%

Radiative hydrodynamic modelling and observations of the X-class solar flare on 2011 March 9

Kennedy

Milligan

Allred

et al. 2015

A&A

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Aims. We investigated the response of the solar atmosphere to non-thermal electron beam heating using the radiative transfer and hydrodynamics modelling code RADYN. The temporal evolution of the parameters that describe the non-thermal electron energy distribution were derived from hard X-ray observations of a particular flare, and we compared the modelled and observed parameters. Methods. The evolution of the non-thermal electron beam parameters during the X1.5 solar flare on 2011 March 9 were obtained from analysis of RHESSI X-ray spectra. The RADYN flare model was allowed to evolve for 110 s, after which the electron beam heating was ended, and was then allowed to continue evolving for a further 300 s. The modelled flare parameters were compared to the observed parameters determined from extreme-ultraviolet spectroscopy. Results. The model produced a hotter and denser flare loop than that observed and also cooled more rapidly, suggesting that additional energy input in the decay phase of the flare is required. In the explosive evaporation phase a region of high-density cool material propagated upward through the corona. This material underwent a rapid increase in temperature as it was unable to radiate away all of the energy deposited across it by the non-thermal electron beam and via thermal conduction. A narrow and high-density (n e ≤ 10 15 cm −3 ) region at the base of the flare transition region was the source of optical line emission in the model atmosphere. The collision-stopping depth of electrons was calculated throughout the evolution of the flare, and it was found that the compression of the lower atmosphere may permit electrons to penetrate farther into a flaring atmosphere compared to a quiet Sun atmosphere.

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Section: Modelmentioning

confidence: 99%

Radiative hydrodynamic modelling and observations of the X-class solar flare on 2011 March 9

Kennedy

Milligan

Allred

et al. 2015

A&A

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“…We use Voigt profiles with complete redistribution (CRD) for all lines. For the Lyman lines, profiles truncated at six Doppler widths are used to mimic effects of partial redistribution (PRD) (Milkey & Mihalas 1973).…”

Section: Hydrogenmentioning

confidence: 99%

Approximations for radiative cooling and heating in the solar chromosphere

Carlsson

Leenaarts

2012

A&A

185

163

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Context. The radiative energy balance in the solar chromosphere is dominated by strong spectral lines that are formed out of LTE. It is computationally prohibitive to solve the full equations of radiative transfer and statistical equilibrium in 3D time dependent MHD simulations. Aims. We look for simple recipes to compute the radiative energy balance in the dominant lines under solar chromospheric conditions. Methods. We use detailed calculations in time-dependent and 2D MHD snapshots to derive empirical formulae for the radiative cooling and heating. Results. The radiative cooling in neutral hydrogen lines and the Lyman continuum, the H and K and intrared triplet lines of singly ionized calcium and the h and k lines of singly ionized magnesium can be written as a product of an optically thin emission (dependent on temperature), an escape probability (dependent on column mass) and an ionization fraction (dependent on temperature). In the cool pockets of the chromosphere the same transitions contribute to the heating of the gas and similar formulae can be derived for these processes. We finally derive a simple recipe for the radiative heating of the chromosphere from incoming coronal radiation. We compare our recipes with the detailed results and comment on the accuracy and applicability of the recipes.

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“…Given the model atmosphere the levels up to 2 may be affected but at the optical depths ∼0.1 for the Lyman continuum the effect to level populations may also come from the (log) column mass points <−5 (e.g. Milkey & Mihalas 1973). We considered the computations in both detailed balance and with properly recomputed radiative rates but the gross effect on the hydrogen alpha transition is very small.…”

Section: Lyman-lines Balance and Level Populationsmentioning

confidence: 99%

An atmospheric model for UZ Librae from mean Hα-line profiles

Zboril¹,

Strassmeier²,

Avrett³

2004

A&A

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Abstract. We present the results from fitting a semi-empirical atmospheric model including a chromosphere and a transition region to the mean (seasonal) Balmer Hα line profiles of the RS CVn-type K0-giant UZ Librae. As a first step, a static 1D spherical model was applied to the mean component of the Hα-emission core and its profile. The main result of the fitting is that the transition region begins at a log mass depth of −1.8 g cm −2 at a temperature of 7400 K (approximately 3000 K warmer than the photosphere) and then has a steep increase to the peak temperature of ≈10 6 K. A stellar model in plane-parallel mode with "partial-frequency redistribution" option in the line transfer gave roughly the best fit. Subsequently, two-Gaussian fitting of the phase-dependent Hα-line profiles yields a complex velocity field. The radial velocities, from both the absorption reversal and the main emission component, display rotational and/or orbital modulation. The largest differences between consecutive line profiles occur mostly in the red line wings, suggesting the existence of both an inward-pointed velocity field and sporadic radiation events possibly related to flares. The total Hα emission, as derived from the equivalent width, possibly also displays rotational modulation. Indirect evidence is presented for the existence of circumstellar matter in form of an Hα absorption shell. Finally, a preliminary elemental abundance analysis suggests sub-solar metallicity of [M/H] ≈ −0.5 dex based on ATLAS models, or −0.7 dex based on PHOENIX models.

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Resonance-Line Transfer with Partial Redistribution: a Preliminary Study of Lyman a in the Solar Chromosphere

Cited by 63 publications

References 0 publications

Radiative hydrodynamic modelling and observations of the X-class solar flare on 2011 March 9

Radiative hydrodynamic modelling and observations of the X-class solar flare on 2011 March 9

Approximations for radiative cooling and heating in the solar chromosphere

An atmospheric model for UZ Librae from mean Hα-line profiles

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