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 CHIANTI spectral code consists of two parts: an atomic database and a suite of computer programs in Python and IDL. Together, they allow the calculation of the optically thin spectrum of astrophysical objects and provide spectroscopic plasma diagnostics for the analysis of astrophysical spectra. The database includes atomic energy levels, wavelengths, radiative transition probabilities, collision excitation rate coefficients, ionization, and recombination rate coefficients, as well as data to calculate free-free, free-bound, and two-photon continuum emission. Version 7.1 has been released, which includes improved data for several ions, recombination rates, and element abundances. In particular, it provides a large expansion of the CHIANTI models for key Fe ions from Fe VIII to Fe XIV to improve the predicted emission in the 50-170 A wavelength range. All data and programs are freely available at http://www.chiantidatabase.org and in SolarSoft, while the Python interface to CHIANTI can be found at http://chiantipy.sourceforge.net.

https://iopscience.iop.org/article/10.1088/0004-637X/763/2/86/pdf

Chianti—an atomic database for emission lines. xiii. soft x-ray improvements and other changes

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.

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CHIANTI – An atomic database for emission lines. Version 8

We use a sample of 45 low-metallicity H II regions to determine the primordial helium abundance Y p with a precision of better than 1%. The data includes new spectrophotometric observations of 15 blue compact galaxies (BCGs) with oxygen abundance 12 ) log (O/H) between 7.83 and 8.35 (Z _ /13 " Z " most of which were selected from the First Byurakan and the University of Michigan objective Z _ /4), prism surveys. We have included many low-metallicity BCGs in our sample, including the two most metal-de-cient galaxies known, I Zw 18 and SBS 0335(052 We have carefully investi- (Z _ /55) (Z _ /43). gated the physical e†ects that may make the He I line intensities deviate from their recombination values, such as collisional and Nuorescent enhancements, underlying He I stellar absorption, and absorp- tion by Galactic interstellar Na I. By extrapolating the Y versus O/H and Y versus N/H linear regres- sions to O/H \ N/H \ 0, we obtain and 0.245 ^ 0.001, respectively, in agreement Y p \ 0.244 ^ 0.002 with the study of Izotov, Thuan, & Lipovetsky, but higher than previous determinations (Y p \ 0.230E0.234). Part of the di†erence comes from the fact that previous investigators have used the north- west component of I Zw 18 in the determination of This component is subject to strong underlying Y p . He I stellar absorption that reduces the He I line intensities by 5%E25%. The derived Y is 0.233 ^ 0.008 from the He I j6678 line. Instead, by using the southeast component of I Zw 18, which is much less subject to underlying He I stellar absorption, we obtain Y \ 0.242 ^ 0.009. The mean Y of the two most metal-de-cient BCGs, I Zw 18 and SBS 0335(052, is in excellent agreement with the Y1 \ 0.245 ^ 0.004, derived from the linear regressions. We derive a slope dY /dZ \ 2.3 ^ 1.0, considerably smaller than Y p those derived before. With this smaller slope and taking into account the errors, chemical evolution models with an outNow of well-mixed material can be built for star-forming dwarf galaxies that satisfy all the observational constraints. Our gives consistent with the lower limit set Y p ) b h 50 0.058 ^ 0.007, by dynamical measurements and X-ray observations of clusters of galaxies. It is also consistent, within the framework of standard big bang nucleosynthesis theory, with measurements of primordial 7Li in galactic halo stars, and at the 1 p level with the D/H abundance measured in absorption systems toward quasars by Tytler & Burles. Subject headings: galaxies: abundances E galaxies: irregular E galaxies: ISM E H II regions E ISM: abundances

The Primordial Abundance of 4He Revisited

We present the results of optically thick non-LTE radiative transfer calculations of lines and continua of H, C I-IV, and O I-VI and other elements using a new one-dimensional, time-independent model corresponding to the average quiet-Sun chromosphere and transition region. The model is based principally on the Curdt et al. SUMER atlas of the extreme ultraviolet spectrum. Our model of the chromosphere is a semiempirical one, with the temperature distribution adjusted to obtain optimum agreement between calculated and observed continuum intensities, line intensities, and line profiles. Our model of the transition region is determined theoretically from a balance between (a) radiative losses and (b) the downward energy flow from the corona due to thermal conduction and particle diffusion, and using boundary conditions at the base of the transition region established at the top of the chromosphere from the semiempirical model. The quiet-Sun model presented here should be considered as a replacement of the earlier model C of Vernazza et al., since our new model is based on an energy-balance transition region, a better underlying photospheric model, a more extensive set of chromospheric observations, and improved calculations. The photospheric structure of the model given here is the same as in Table 3 of Fontenla, Avrett, Thuiller, & Harder. We show comparisons between calculated and observed continua, and between the calculated and observed profiles of all significant lines of H, C I-IV, and O I-VI in the wavelength range 67-173 nm. While some of the calculated lines are not in emission as observed, we find reasonable general agreement, given the uncertainties in atomic rates and cross sections, and we document the sources of the rates and cross sections used in the calculation. We anticipate that future improvements in the atomic data will give improved agreement with the observations.

https://iopscience.iop.org/article/10.1086/523671/pdf

Models of the Solar Chromosphere and Transition Region from SUMER and HRTS Observations: Formation of the Extreme-Ultraviolet Spectrum of Hydrogen, Carbon, and Oxygen

New improved calculations are reported for transition probabilities and electron impact excitation collision strengths for the astrophysically important lines in S II. The collision strengths have been calculated in the close-coupling approximation using the B-spline Breit-Pauli R-matrix method. The multiconfiguration Hartree-Fock method with term-dependent non-orthogonal orbitals is employed for an accurate representation of the target wave functions. The close-coupling expansion includes 70 bound levels of S II covering all possible terms of the ground 3s 23p 3 and singly excited 3s3p 4, 3s 23p 23d, 3s 23p 24s, and 3s 23p 24p configurations. The present calculations are more extensive than previous ones, leading to a total 2415 transitions between fine-structure levels. The effective collision strengths are obtained by averaging the electron collision strengths over a Maxwellian distribution of velocities and these are tabulated for all fine-structure transitions at electron temperatures in the range from 5000 to 100,000 K. The present results are compared with a variety of other close-coupling calculations and available experimental data. There is an overall good agreement with the recent 18-state calculations by Ramsbottom, Bell, & Stafford and with the 19-state calculations by Tayal for the most part, but some significant differences are also noted for some transitions.

https://iopscience.iop.org/article/10.1088/0067-0049/188/1/32/pdf

Breit-Pauli Transition Probabilities and Electron Excitation Collision Strengths for Singly Ionized Sulfur

Collision strengths for the astrophysically important lines in N II have been calculated in the close-coupling approximation using the B-spline Breit-Pauli R-matrix method. The multiconfiguration Hartree-Fock method with term-dependent non-orthogonal orbitals is employed for an accurate representation of the target wave functions. The close-coupling expansion includes 58 bound levels of N II. The 58 target levels belong to the terms of the ground 2s 22p 2 and singly excited 2s2p 3, 2s 22p3s, 2s 22p3p, 2s 22p3d, 2s 22p4s, 2s 22p4p, and 2s2p 23s configurations. The effective collision strengths are obtained by averaging the electron collision strengths over a Maxwellian distribution of velocities and these are tabulated for all 1653 fine-structure transitions among the 58 levels at electron temperatures in the range from 500 to 100,000 K. The line strengths, oscillator strengths, and transition probabilities for all E1 transitions are tabulated. The present results are compared with a variety of other close-coupling calculations. There is an overall good agreement with the 23-state calculation by Hudson & Bell in most part, but some significant differences are also noted for some transitions.

http://iopscience.iop.org/article/10.1088/0067-0049/195/2/12/pdf

Electron excitation collision strengths for singly ionized nitrogen

The B-spline R-matrix approach has been used to calculate electron collisional excitation strengths and rates for transitions between the 3P, 1D, and 1S states of ground configuration and from these states to the states of the excited 2s(sup 2)2p(sup 3)ns (n = 3-5), 2s(sup 2)2p(sup 3)np (n = 3-4), 2s(sup 2)2p(sup 3)nd (n = 3-4), 2s(sup 2)2p(sup 3)4f, and 2s2p(sup 5) configurations. The nonorthogonal orbitals are used for an accurate description of both the target wave functions and the R-matrix basis functions. The thermally averaged collision strengths are obtained from the collision strengths by integrating over a Maxwellian velocity distribution of electron energies, and these are tabulated over a temperature range from 1000 to 60,000 K. The parametric functions of scaled energy have also been obtained to represent collision strengths over a wide energy range or thermally averaged collision strengths at any desired temperature.

Electron Collisional Excitation Rates for O I Using the B-Spline R-Matrix Approach

Electron scattering with atomic oxygen has been studied using the $B$-spline $R$-matrix-with-pseudostates method. Cross sections for elastic scattering, excitation, emission, and ionization processes are presented. The excitation cross sections have been calculated for transitions between the $2{s}^{2}2{p}^{4}$ and $2{s}^{2}2{p}^{3}3l$ states of oxygen in the energy range from threshold to 200 eV. The present work differs from numerous previous studies due to the inclusion of a large number of pseudostates in the calculation. We included a total of 1116 spectroscopic bound, core-excited autoionizing, and target continuum states in the close-coupling expansion. The atomic oxygen structure model has been described by combining the multiconfiguration Hartree-Fock and the $B$-spline box-based multichannel methods. The inclusion of a large number of pseudostates representing the target continuum has a major impact, especially on the theoretical prediction of the excitation cross sections for many transitions at intermediate energies. A large reduction in excitation and emission cross sections has been noted due to the inclusion of coupling to the ionization continuum. The calculated cross sections are now in better agreement with available experimental results. The ionization cross sections for the ground $2{s}^{2}\phantom{\rule{0.16em}{0ex}}2{p}^{4}{\phantom{\rule{0.16em}{0ex}}}^{3}P$ and metastable $2{s}^{2}2{p}^{4}{\phantom{\rule{0.16em}{0ex}}}^{1}D$ and $^{1}S$ states are also presented. The electron-impact-induced emission cross sections for the $(2{s}^{2}2{p}^{3}3s){\phantom{\rule{0.16em}{0ex}}}^{3}{S}^{o}--(2{s}^{2}2{p}^{4}){\phantom{\rule{0.16em}{0ex}}}^{3}P$ (130.4 nm), $(2{s}^{2}2{p}^{3}3d){\phantom{\rule{0.16em}{0ex}}}^{3}{D}^{o}--(2{s}^{2}2{p}^{4}){\phantom{\rule{0.16em}{0ex}}}^{3}P$ (102.7 nm), $(2{s}^{2}2{p}^{3}3{s}^{\ensuremath{'}}){\phantom{\rule{0.16em}{0ex}}}^{3}{D}^{o}--(2{s}^{2}2{p}^{4}){\phantom{\rule{0.16em}{0ex}}}^{3}P$ (98.9 nm), and $(2{s}^{2}2{p}^{3}3{s}^{\ensuremath{'}\ensuremath{'}}){\phantom{\rule{0.16em}{0ex}}}^{3}{D}^{o}--(2{s}^{2}2{p}^{4}){\phantom{\rule{0.16em}{0ex}}}^{3}P$ (87.8 nm) transitions have been calculated and compared with the available experimental results.

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B -spline R -matrix-with-pseudostates approach for excitation and ionization of atomic oxygen by electron collisions

Electron impact excitation collision strengths and rates for transitions between fine-structure levels of the 3s2np (n = 3–6), 3s3p2, 3s2ns (n = 4–6), 3s2nd (n = 3–5), 3s2nf (n = 4–5), and 3s3p3d configurations in Si II are calculated by using the Breit-Pauli B-spline R-matrix approach. The 31 target levels have been included in the close-coupling expansion in our collision calculation. The multiconfiguration Hartree-Fock method with term-dependent nonorthogonal orbitals is employed for an accurate representation of the target wave functions. The target levels have been described by using both spectroscopic and correlation radial functions. The atomic wave functions yield excitation energies that are in excellent agreement with experiment and other reliable calculations. The relativistic corrections are included through the one-body mass correction, Darwin, and spin-orbit operators in the Breit-Pauli Hamiltonian. The effective collision strengths have been calculated by integrating total resonant and nonresonant collision strengths over a Maxwellian distribution of electron energies, and these are presented over a wide temperature range suitable for modeling of astrophysical plasmas. Significant differences are noted with the previous eight-state R-matrix calculation, particularly for transitions involving higher excitation levels.

http://iopscience.iop.org/article/10.1086/591849/pdf

S. S. Tayal

Papers

Breit-Pauli Transition Probabilities and Electron Excitation Collision Strengths for Singly Ionized Sulfur

Electron excitation collision strengths for singly ionized nitrogen

Electron Collisional Excitation Rates for O I Using the B-Spline R-Matrix Approach

B -spline R -matrix-with-pseudostates approach for excitation and ionization of atomic oxygen by electron collisions

Collision Strengths for Electron Scattering from Si II