The ionization equilibrium of astrophysically abundant elements

Shull, J. M.; Steenberg, Michael E. Van

doi:10.1086/190769

Cited by 465 publications

(375 citation statements)

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“…In H ii regions, where the electron densities are typically N e ¼ 10 2 10 3 cm À3 , collisions are therefore not the dominant mechanism governing the Si ii level populations. Also, when T $ 10 4 K and Si ii and Si iii have comparable abundances (as appropriate here), it can be shown that the recombination rate of Si iii into the excited Si ii levels is of the same order as the Si ii collisional excitation rates (Shull & van Steenberg 1982). In order to understand the origin of the Si ii* emission lines in a more systematic way, we modeled all observed LBG nebular emission lines using the CLOUDY96 software package (Ferland et al 1998).…”

Section: Si Ii* Linesmentioning

confidence: 99%

Rest‐Frame Ultraviolet Spectra of \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} \normalfont \selectfont} \DeclareTextFontCommand{\textcyr}{\cyr} \pagestyle{empty} \De

Shapley

Steidel

Pettini

et al. 2003

ApJ

1,255

148

999

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We present the results of a systematic study of the rest-frame UV spectroscopic properties of Lyman break galaxies (LBGs). The database of almost 1000 LBG spectra proves useful for constructing high signalto-noise composite spectra. The composite spectrum of the entire sample reveals a wealth of features attributable to hot stars, H ii regions, dust, and outflowing neutral and ionized gas. By grouping the database according to galaxy parameters such as Ly equivalent width, UV spectral slope, and interstellar kinematics, we isolate some of the major trends in LBG spectra that are least compromised by selection effects. We find that LBGs with stronger Ly emission have bluer UV continua, weaker low-ionization interstellar absorption lines, smaller kinematic offsets between Ly and the interstellar absorption lines, and lower star formation rates. There is a decoupling between the dependence of low-and high-ionization outflow features on other spectral properties. Additionally, galaxies with rest-frame W Ly ! 20 Å in emission have weaker than average high-ionization lines and nebular emission lines that are significantly stronger than in the sample as a whole. Most of the above trends can be explained in terms of the properties of the large-scale outflows seen in LBGs. According to this scenario, the appearance of LBG spectra is determined by a combination of the covering fraction of outflowing neutral gas, which contains dust and the range of velocities over which this gas is absorbing. In contrast, the strengths of collisionally excited nebular emission lines should not be affected by the nature of the outflow, and variations in these lines may indicate differences in the temperatures and metallicities in H ii regions of galaxies with very strong Ly emission. Higher sensitivity and spectral resolution observations are still required for a full understanding of the covering fraction and velocity dispersion of the outflowing neutral gas in LBGs and its relationship to the escape fraction of Lyman continuum radiation in galaxies at z $ 3.

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Section: Si Ii* Linesmentioning

confidence: 99%

Rest‐Frame Ultraviolet Spectra of \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} \normalfont \selectfont} \DeclareTextFontCommand{\textcyr}{\cyr} \pagestyle{empty} \De

Shapley

Steidel

Pettini

et al. 2003

ApJ

1,255

148

999

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“…The parameters C RR and η were taken from Aldrovandi & Pequignot (1973), Landini & Monsignori Fossi (1990), Shull & van Steenberg (1982), Mazzotta et al (1998), andBadnell (2006b). For the dielectronic recombination rate, the following expression, valid for any distribution function, has been used (Dzifčáková 1992;Dzifčáková & Dudík 2013) …”

Section: Calculation Of Synthetic X-ray Line Spectramentioning

confidence: 99%

Shock-reflected electrons and X-ray line spectra

Dzifčáková

Vandas

Karlický

2017

A&A

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Aims. The aim of this paper is to try to explain the physical origin of the non-thermal electron distribution that is able to form the enhanced intensities of satellite lines in the X-ray line spectra observed during the impulsive phases of some solar flares. Methods. Synthetic X-ray line spectra of the distributions composed of the distribution of shock reflected electrons and the background Maxwellian distribution are calculated in the approximation of non-Maxwellian ionization, recombination, excitation and de-excitation rates. The distribution of shock reflected electrons is determined analytically. Results. We found that the distribution of electrons reflected at the nearly-perpendicular shock resembles, at its highenergy part, the so called n-distribution. Therefore it could be able to explain the enhanced intensities of Si xiid satellite lines. However, in the region immediately in front of the shock its effect is small because electrons in background Maxwellian plasma are much more numerous there. Therefore, we propose a model in which the shock reflected electrons propagate to regions with smaller densities and different temperatures. Combining the distribution of the shock-reflected electrons with the Maxwellian distribution having different densities and temperatures we found that spectra with enhanced intensities of the satellite lines are formed at low densities and temperatures of the background plasma when the combined distribution is very similar to the n-distribution also in its low-energy part. In these cases, the distribution of the shock-reflected electrons controls the intensity ratio of the allowed Si xiii and Si xiv lines to the Si xiid satellite lines. The high electron densities of the background plasma reduce the effect of shock-reflected electrons on the composed electron distribution function, which leads to the Maxwellian spectra.

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“…Column 1: element, Col. 2: number of fine-structure levels solved for and the number included in the radiative transfer, Col. 3: highest state included, Col. 4: source for level energies and transition A-values, Col. 5: source for the total radiative recombination rate, Col. 6: source for the specific radiative recombination rates, and the number of levels for which these rates are included in parenthesis, Col. 7: source for the (thermal) collision strengths, and the number of levels with collision strength included in parenthesis. Shull & van Steenberg (1982); (20) Trail et al (1994); (21) Verner et al (1996); (22) Zhang & Pradhan (1995); (23) NIST (www.nist.gov); (24) TOPBASE (http://cdsweb. u-strasbg.fr/topbase/xsections.html); (25) Almog & Netzer (1989).…”

Section: Appendix A: Atomic Datamentioning

confidence: 99%

The⁴⁴Ti-powered spectrum of SN 1987A

Jerkstrand

Fransson

Kozma

2011

A&A

171

249

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SN 1987A provides a unique opportunity to study the evolution of a supernova from explosion into very late phases. Owing to the rich chemical structure, the multitude of physical processes involved and extensive radiative transfer effects, detailed modeling is needed to interpret the emission from this and other supernovae. In this paper, we analyze the late-time (about eight years) Hubble Space Telescope spectrum of the SN 1987A ejecta, where 44 Ti is the dominant power source. Based on an explosion model for a 19 M progenitor, we compute a model spectrum by calculating the degradation of positrons and gamma-rays from the radioactive decays, solving the equations governing temperature, ionization balance and NLTE level populations, and treating the radiative transfer with a Monte Carlo technique. We obtain a UV/optical/NIR model spectrum that reproduces most of the lines in the observed spectrum with good accuracy. We find non-local radiative transfer in atomic lines to be an important process also at this late stage of the supernova, with ∼30% of the emerging flux in the optical and NIR coming from scattering/fluorescence. We investigate the question of where the positrons deposit their energy, and favor the scenario where they are locally trapped in the Fe/He clumps by a magnetic field. Energy deposition into these largely neutral Fe/He clumps makes Fe I lines prominent in the emerging spectrum. With the best available estimates for the dust extinction, we determine the amount of 44 Ti produced in the explosion to be 1.5 +0.5 −0.5 × 10 −4 M .

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The ionization equilibrium of astrophysically abundant elements

Cited by 465 publications

References 0 publications

Shock-reflected electrons and X-ray line spectra

The⁴⁴Ti-powered spectrum of SN 1987A

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The ionization equilibrium of astrophysically abundant elements

Cited by 465 publications

References 0 publications

Shock-reflected electrons and X-ray line spectra

The44Ti-powered spectrum of SN 1987A

Contact Info

Product

Resources

About

The⁴⁴Ti-powered spectrum of SN 1987A