Physical Processes in Gaseous Nebulae. X. Collisional Excitation of Nebulium.

Hebb, Malcolm H.; Menzel, Donald H.

doi:10.1086/144230

Cited by 64 publications

(13 citation statements)

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“…where T is the temperature of plasma (electron temperature), w i is the statistical weight of level i,Ω(y) is the effective collision strength (Hebb & Menzel 1940, also called the Upsilon value), E i j is the excitation energy for the transition i → j and S 0 is the constant defined as…”

Section: Radiative Loss Due To Collisional Excitation In Low-density Plasmasmentioning

confidence: 99%

New radiative loss curve from updates to collisional excitation in the low-density, optically thin plasmas in SPEX

Štofanová

Kaastra

Mehdipour

et al. 2021

A&A

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Understanding and modelling astrophysical plasmas on atomic levels while taking into account various assumptions (for example, collisional ionisation equilibrium or photoionisation equilibrium) became essential with the progress of high-resolution X-ray spectroscopy. In order to prepare for the upcoming X-ray spectroscopy missions such as XRISM or Athena, the plasma codes with their models and the atomic databases need to be up to date and accurate. One such update for the plasma code SPEX is presented in this paper where we focus on the radiative loss due to collisional excitation in the low-density, optically thin regime. We also update the atomic data for neutral hydrogen and include the contribution of the dielectronic recombination. With all these updates being implemented in SPEX we finally present the new cooling curve. We include the comparison to other plasma codes (MEKAL, APEC, Cloudy) and other atomic databases (CHIANTI, ADAS). We show how the updated cooling impacts the stability curve for photoionised plasmas and find a new stable branch.

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Section: Radiative Loss Due To Collisional Excitation In Low-density Plasmasmentioning

confidence: 99%

New radiative loss curve from updates to collisional excitation in the low-density, optically thin plasmas in SPEX

Štofanová

Kaastra

Mehdipour

et al. 2021

A&A

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“…Calculating these rates was a very complicated problem. The first realistic calculations of the excitation cross sections for O 2+ by electron impact were done only in 1940 [16].…”

Section: Determining the Electron Temperature From The Lines Of Nebuliummentioning

confidence: 99%

Plasma diagnostics of planetary nebulae

Холтыгин

2008

Astrophysics

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Diagnostics for the rarefied plasmas in gaseous nebulae are reviewed, beginning with the pioneering papers of V. A. Ambartsumian. These papers, as well as the diagnostic techniques which have been developed on the basis of ideas contained in them, are discussed. Diagnostic techniques for homogeneous, as well as inhomogeneous, plasmas are described.Keywords: planetary nebulae: interstellar medium; plasma diagnostics nuclei of planetary nebulae. At present, the number of observed planetary nebulae in our galaxy is approaching two thousand. Many planetary nebulae have also been found in other galaxies, including spiral (M31, M33, etc.) as well as irregular and elliptical galaxies.The spectra of gaseous nebulae differ significantly from those of stars. They consist of a weak continuum spectrum and a large number of intense emission lines, of which the lines of hydrogen and ionized and neutral helium dominate in the visible range. However, the brightest lines in the spectra of nebulae, with wavelengths λ5007 Å and λ4959 Å were not identified for a long time, since they did not show up in the spectra of elements studied in earthbound laboratories. For this reason they were assumed to belong to an unknown element, nebulium. They were thus denoted by N 1 and N 2 (the nebulium 1 and nebulium 2 lines).The nature of the nebular emission in these lines was understood only after the development of quantum mechanics. In 1928 the American astrophysicist Bowen showed [1] that the N 1 and N 2 lines are forbidden lines of the O 2+ ion and are transitions from metastable levels of this ion. He also showed that the bright 3729 3726 + λ Å doublet in the spectra of nebulae is associated with forbidden transitions of singly ionized oxygen O + . This discovery was an indication of the low density of both matter and radiation in nebulae. V. A. Ambartsumian's papers on gaseous nebulaeAmbartsumian's papers on the spectra of planetary and diffuse nebulae (all are collected in Volume 1 of his Scientific Papers [4]) were published in the 1930's. This was a time when theoretical astrophysics was being founded and research on gaseous nebulae was at its frontier.His first paper in this area [5] is devoted to determining the temperature of the nuclei of planetary nebulae.He proposed an original method for determining the temperature based on comparing the energy β H E emitted by the nebula in the Hβ line to the energy 4686 λ E emitted in the HeII λ4686 line. Here it is assumed that all the UV photons emitted by the central star of the nebula, and capable of ionizing hydrogen atoms and helium ions, are absorbed in the nebula. This method, known as Ambartsumian's method, yielded realistic estimates of the temperatures of the central stars that are close to their modern values.

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“…The assumption that the velocity distribution of the free electrons in gaseous nebulae are described by a M-B distribution dates back to, at least, the 1930s, when the treatments of the physical state of Planetary Nebulae (PNe) already used this distribution (e.g. Bohm & Aller 1947;Hebb & Menzel 1940). This assumption is based on the electron thermalization timescale, the timescale a free electron requires to become thermalized and described by the M-B distribution (e.g.…”

Section: Introductionmentioning

confidence: 99%

Electron Energy Distributions in the Extended Gas Nebulae associated with High-z AGN: Maxwell-Boltzmann vs. kappa distributions

Morais,

Humphrey,

Martín

et al. 2021

Preprint

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Emission line observations together with photoionization models provide important information about the ionization mechanisms, densities, temperatures, and metallicities in AGN-ionized gas. Photoionization models usually assume Maxwell-Boltzmann (M-B) electron energy distributions (EED), but it has been suggested that using κ distributions may be more appropriate and could potentially solve the discrepancies in temperatures and abundances found in HII regions and Planetary Nebulae (PNe). We consider the impact of the presence of κ distributions in photoionized nebulae associated with AGN and study how this might affect spectral modelling and abundance analyses for such regions. Using the photoionization code MAP-PINGS 1e we compute models adopting M-B and κ distributions of electron energies, and compare the behaviour of emission line ratios for different values of κ, gas metallicity, density, ionization parameter and SED slope. We find that the choice of EED can have a large impact on some UV and optical emission lines emitted by photoionized nebulae associated with AGN, and that the impact of adopting a κ distribution is strongly dependent on gas metallicity and ionization parameter. We compile a sample of line ratios for 143 type 2 AGN and compare our models against the observed line ratios. We find that for 98 objects κ distributions provide a better fit to the observed line ratios than M-B distributions. In addition, we find that adopting κ-distributed electron energies results in significant changes in the inferred gas metallicity and ionization parameter in a significant fraction of objects.

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Physical Processes in Gaseous Nebulae. X. Collisional Excitation of Nebulium.

Cited by 64 publications

References 0 publications

New radiative loss curve from updates to collisional excitation in the low-density, optically thin plasmas in SPEX

New radiative loss curve from updates to collisional excitation in the low-density, optically thin plasmas in SPEX

Plasma diagnostics of planetary nebulae

Electron Energy Distributions in the Extended Gas Nebulae associated with High-z AGN: Maxwell-Boltzmann vs. kappa distributions

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