CLOUDY is a large‐scale spectral synthesis code designed to simulate fully physical conditions within an astronomical plasma and then predict the emitted spectrum. Here we describe version 90 (C90) of the code, paying particular attention to changes in the atomic database and numerical methods that have affected predictions since the last publicly available version, C84. The computational methods and uncertainties are outlined together with the direction future development will take. The code is freely available and is widely used in the analysis and interpretation of emission‐line spectra. Web access to the Fortran source for CLOUDY, its documentation Hazy, and an independent electronic form of the atomic database is also described.

https://iopscience.iop.org/article/10.1086/316190/pdf

CLOUDY 90: Numerical Simulation of Plasmas and Their Spectra

This is a comprehensive and richly illustrated textbook on the astrophysics of the interstellar and intergalactic medium--the gas and dust, as well as the electromagnetic radiation, cosmic rays, and magnetic and gravitational fields, present between the stars in a galaxy and also between galaxies themselves. Topics include radiative processes across the electromagnetic spectrum; radiative transfer; ionization; heating and cooling; astrochemistry; interstellar dust; fluid dynamics, including ionization fronts and shock waves; cosmic rays; distribution and evolution of the interstellar medium; and star formation. While it is assumed that the reader has a background in undergraduate-level physics, including some prior exposure to atomic and molecular physics, statistical mechanics, and electromagnetism, the first six chapters of the book include a review of the basic physics that is used in later chapters. This graduate-level textbook includes references for further reading, and serves as an invaluable resource for working astrophysicists. * Essential textbook on the physics of the interstellar and intergalactic medium * Based on a course taught by the author for more than twenty years at Princeton University * Covers radiative processes, fluid dynamics, cosmic rays, astrochemistry, interstellar dust, and more * Discusses the physical state and distribution of the ionized, atomic, and molecular phases of the interstellar medium * Reviews diagnostics using emission and absorption lines * Features color illustrations and detailed reference materials in appendices * Instructor's manual with problems and solutions (available only to teachers)

Physics of the Interstellar and Intergalactic Medium

The Earth's ultraviolet airglow contains fundamental diagnostic information about the state of its upper atmosphere and ionosphere. Our understanding of the excitation and emission processes which are responsible for the airglow has undergone dramatic evolution from the earliest days of space research through the past several years during which a wealth of new information has been published from high-resolution spectroscopy and imaging experiments. This review of the field begins with an overview of the phenomenology: how the Earth looks in the ultraviolet. Next the basic processes leading to excitation of atomic and molecular energy states are discussed. These concepts are developed from first principles and applied to selected examples of day and night airglow; a detailed review of radiation transport theory is included. This is followed by a comprehensive examination of the current status of knowledge of individual emission features seen in the airglow, in which atomic physics issues as well as relevant atmospheric observations of major and minor neutral and ionic constituents are addressed. The use of airglow features as remote sensing observables is then examined for the purpose of selecting those species most useful as diagnostics of the state of the thermosphere and ionosphere. Imaging of the plasmasphere and magnetosphere is also briefly considered. A summary of upcoming UV remote sensing missions is provided.

Ultraviolet spectroscopy and remote sensing of the upper atmosphere

We present version 8 of the CHIANTI database. This version includes a large amount of new data and ions, which represent a significant improvement in the soft X-ray, extreme UV (EUV) and UV spectral regions, which several space missions currently cover. New data for neutrals and low charge states are also added. The data are assessed, but to improve the modelling of low-temperature plasma the effective collision strengths for most of the new datasets are not spline-fitted as previously, but are retained as calculated. This required a change of the format of the CHIANTI electron excitation files. The format of the energy files has also been changed. Excitation rates between all the levels are retained for most of the new datasets, so the data can in principle be used to model high-density plasma. In addition, the method for computing the differential emission measure used in the CHIANTI software has been changed.

/pdf/chianti-an-atomic-database-for-emission-lines-version-8-3c637uz4bs.pdf

CHIANTI – An atomic database for emission lines. Version 8

We use high signal-to-noise ratio spectra of 20 H II regions in the giant spiral galaxy M101 to derive electron temperatures for the H II regions and robust metal abundances over radii R = 019-125R0 (6-41 kpc) We compare the consistency of electron temperatures measured from the [O III] ?4363, [N II] ?5755, [S III] ?6312, and [O II] ?7325 auroral lines Temperatures from [O III], [S III], and [N II] are correlated with relative offsets that are consistent with expectations from nebular photoionization models However, the temperatures derived from the [O II] ?7325 line show a large scatter and are nearly uncorrelated with temperatures derived from other ions We tentatively attribute this result to observational and physical effects, which may introduce large random and systematic errors into abundances derived solely from [O II] temperatures Our derived oxygen abundances are well fitted by an exponential distribution over six disk scale lengths, from approximately 13 (O/H)? in the center to 1/15 (O/H)? in the outermost region studied [for solar 12 + log(O/H) = 87] We measure significant radial gradients in N/O and He/H abundance ratios, but relatively constant S/O and Ar/O Our results are in approximate agreement with previously published abundances studies of M101 based on temperature measurements of a few H II regions However, our abundances are systematically lower by 02-05 dex than those derived from the most widely used strong-line empirical abundance indicators, again consistent with previous studies based on smaller H II region samples Independent measurements of the Galactic interstellar oxygen abundance from ultraviolet absorption lines are in good agreement with the Te-based nebular abundances We suspect that most of the disagreement with the strong-line abundances arises from uncertainties in the nebular models that are used to calibrate the empirical scale, and that strong-line abundances derived for H II regions and emission-line galaxies are as much as a factor of 2 higher than the actual oxygen abundances However, other explanations, such as the effects of temperature fluctuations on the auroral line based abundances, cannot be completely ruled out These results point to the need for direct abundance determinations of a larger sample of extragalactic H II regions, especially for objects more metal-rich than solar

https://iopscience.iop.org/article/10.1086/375398/pdf

The Composition Gradient in M101 Revisited. II. Electron Temperatures and Implications for the Nebular Abundance Scale

Electron collisional excitation strengths for transitions between the 3s23p2 3P0,1,2, 1D2, and 1S0 levels and from these levels to the fine-structure levels of the excited 3s3p3, 3s23p3d, 3s23p4s, 3s23p4p, and 3s23p4d configurations of S III are calculated in R-matrix approach. We considered 49 fine-structure levels arising from the 27 LS 3s23p2 3P, 1D, 1S, 3s3p3 5, 3So, 1, 3Do, 1, 3Po, 3s23p3d 1, 3Po, 1,3Do, 1, 3Fo, 3s23p4s 1,3Po, 3s23p4p 1,3S, 1,3P, 1,3D, 3s23p4d 1,3Po, and 1,3Do states. These target levels are represented by fairly extensive configuration-interaction wave functions. The collision strengths for transitions between fine-structure levels are calculated by transforming the LS-coupled K-matrices to K-matrices in an intermediate coupling scheme. Complicated resonance structures converging to excited state thresholds are explicitly included in collision strengths. The effective collision strengths are obtained from the total collision strengths by integrating over a Maxwellian velocity distribution. These are tabulated over a wide electron temperature range (0.5-10) × 104 K.

Collision Strengths for Electron Collision Excitation of Fine-Structure Levels in S III

Electron collision excitation strengths of inelastic transitions among the 52 fine-structure levels of the ground 3s23p and excited 3s3p2, 3s23d, 3s24s, 3p3, 3s24p, 3s3p3d, 3s24d, 3s24f, and 3s3p4s configurations in S IV are calculated using full Breit-Pauli R-matrix method. The target levels are represented by configuration-interaction wave functions, and the mass, Darwin, and spin-orbit relativistic terms are included in the scattering equations. The collision strengths in the threshold energy regions are dominated by the complicated resonance structures. Our collision strengths are compared with earlier available calculations and significant differences are noted. The collision strengths are integrated over a Maxwellian distribution of electron energies to obtain effective collision strengths over a wide temperature range.

http://iopscience.iop.org/article/10.1086/308406/pdf

Electron Collision Excitation of Fine-Structure Levels in S IV

The Dirac-based $B$-spline $R$-matrix method is used to investigate the photoionization of atomic potassium from the $4s$ ground and $4p$, $5s$-$7s$, $3d$-$5d$ excited states. The effect of the core polarization by the outer electron is included through the polarized pseudostates. Besides the dipole core polarization, we also found a noticeable influence of the quadrupole core polarization. We obtained excellent agreement with experiment for cross sections of the $4s$ photoionization, including accurate description of the near-threshold Cooper-Seaton minimum. We also obtained close agreement with experiment for the $4p$ photoionization, but there are unexpectedly large discrepancies with available experimental data for photoionization of the $5d$ and $7s$ excited states.

Photoionization of potassium atoms from the ground and excited states

Electron excitation of fine-structure transitions within the ground 3s2 3p3 configuration in Fe XII

Electron-excitation cross sections are reported for the 3s 2S yields 3p 2P(h, k) resonance transition in Mg(+) at energies from threshold (4.43 eV) to approximately 9 times threshold (40.0 eV). The electron-energy-loss merged-beams technique used in these measurements is described in detail. In addition, the method of separating contributions of the elastically scattered (Coulomb) and the inelastically scattered electrons in the present Mg(+) case and previously reported Zn(+) results is described. Comparisons in the experimental energy range are made for Mg(+) with the two five-state close-coupling theoretical calculations carried out herein, and with other published close-coupling, distorted-wave, and semiempirical calculations. The present Mg(+) cross sections and Zn(+) cross sections from earlier measurements are tabulated.

Excitation cross sections for the ns 2S yields np 2P resonance transitions in Mg(+) (n = 3) and Zn(+) (n = 4) using electron-energy-loss and merged-beams methods

Swaraj Tayal

Papers

Collision Strengths for Electron Collision Excitation of Fine-Structure Levels in S III

Electron Collision Excitation of Fine-Structure Levels in S IV

Photoionization of potassium atoms from the ground and excited states

Electron excitation of fine-structure transitions within the ground 3s2 3p3 configuration in Fe XII

Excitation cross sections for the ns 2S yields np 2P resonance transitions in Mg(+) (n = 3) and Zn(+) (n = 4) using electron-energy-loss and merged-beams methods