We present a new model for computing the spectral evolution of stellar populations at ages between 100,000 yr and 20 Gyr at a resolution of 3 A across the whole wavelength range from 3200 to 9500 A for a wide range of metallicities. These predictions are based on a newly available library of observed stellar spectra. We also compute the spectral evolution across a larger wavelength range, from 91 A to 160 micron, at lower resolution. The model incorporates recent progress in stellar evolution theory and an observationally motivated prescription for thermally-pulsing stars on the asymptotic giant branch. The latter is supported by observations of surface brightness fluctuations in nearby stellar populations. We show that this model reproduces well the observed optical and near-infrared colour-magnitude diagrams of Galactic star clusters of various ages and metallicities. Stochastic fluctuations in the numbers of stars in different evolutionary phases can account for the full range of observed integrated colours of star clusters in the Magellanic Clouds. The model reproduces in detail typical galaxy spectra from the Early Data Release (EDR) of the Sloan Digital Sky Survey (SDSS). We exemplify how this type of spectral fit can constrain physical parameters such as the star formation history, metallicity and dust content of galaxies. Our model is the first to enable accurate studies of absorption-line strengths in galaxies containing stars over the full range of ages. Using the highest-quality spectra of the SDSS EDR, we show that this model can reproduce simultaneously the observed strengths of those Lick indices that do not depend strongly on element abundance ratios [abridged].

https://hal.archives-ouvertes.fr/hal-00012948/document

Stellar population synthesis at the resolution of 2003

The solar chemical composition is an important ingredient in our understanding of the formation, structure, and evolution of both the Sun and our Solar System. Furthermore, it is an essential refer ...

The Chemical Composition of the Sun

Starburst99 is a comprehensive set of model predictions for spectrophotometric and related properties of galaxies with active star formation. The models are an improved and extended version of the data set previously published by Leitherer & Heckman. We have upgraded our code by implementing the latest set of stellar evolution models of the Geneva group and the model atmosphere grid compiled by Lejeune et al. Several predictions which were not included in the previous publication are shown here for the first time. The models are presented in a homogeneous way for five metallicities between Z = 0.040 and 0.001 and three choices of the initial mass function. The age coverage is 106—109 yr. We also show the spectral energy distributions which are used to compute colors and other quantities. The full data set is available for retrieval at a Web site, which allows users to run specific models with nonstandard parameters as well. We also make the source code available to the community.

https://iopscience.iop.org/article/10.1086/313233/pdf

Starburst99: Synthesis Models for Galaxies with Active Star Formation

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

羟氨苄青霉素引起大疱性类天疱疮样疹

Assuming Case B of Baker and Menzel (1938), the relative intensities of H I and He II recombination lines are determined for a larger range of temperature and density than previously considered and with the upper principle quantum number up to 50 and the lower number up to 29. Full collisional effects are included, and new collision strengths for the n = 1, 2, and 3 states of He(+) are presented. Case B theory is found to be invalidated for collisional excitation of the n = 3 levels from both n = 1 and n = 2 states under certain conditions which depend upon electron density and the Lyman-alpha escape probability, and the regimes of temperature and density for which Case B is valid are also considered.

/pdf/recombination-line-intensities-for-hydrogenic-ions-i-case-b-1puj7p0dm8.pdf

Recombination-line intensities for hydrogenic ions – I. Case B calculations for H I and He II

An equation of state for material in stellar envelopes, subject to the limits of temperature less than about 10 to the 7th K and density less than about .01 g/cu cm is presented. The equation makes it possible to express free energy as the sum of several terms representing effects such as partial degeneracy of the electron, Coulomb interactions among charged particles, finite-volume, hard sphere repulsion, and van der Waals attraction. An occupation probability formalism is used to represent the effects of the plasma in establishing a finite partition function. It is shown that the use of the static screened Coulomb potential to calculate level shifts and to estimate the cutoff of the internal partition function is invalid. For most of the parameter space relevant to stellar envelopes, perturbations arising from the plasma ions are shown to be dominant in establishing the internal partition function.

The equation of state for stellar envelopes. I - An occupation probability formalism for the truncation of internal partition functions

A free-energy-minimization method for computing the dissociation and ionization equilibrium of a multicomponent gas is discussed. The adopted free energy includes terms representing the translational free energy of atoms, ions, and molecules; the internal free energy of particles with excited states; the free energy of a partially degenerate electron gas; and the configurational free energy from shielded Coulomb interactions among charged particles. Internal partition functions are truncated using an occupation probability formalism that accounts for perturbations of bound states by both neutral and charged perturbers. The entire theory is analytical and differentiable to all orders, so it is possible to write explicit analytical formulas for all derivatives required in a Newton-Raphson iteration; these are presented to facilitate future work. Some representative results for both Saha and free-energy-minimization equilibria are presented for a hydrogen-helium plasma with N(He)/N(H) = 0.10. These illustrate nicely the phenomena of pressure dissociation and ionization, and also demonstrate vividly the importance of choosing a reliable cutoff procedure for internal partition functions.

The equation of state for stellar envelopes. II - Algorithm and selected results

Section 1..- Recent Advances in Computational Methods.- Acceleration of Convergence.- Fast Solution of Radiative Transfer Problems with a Multi-Grid Method.- Line Blanketing without LTE: Simple and Complex Spectra.- Global and Local Methods for 1-D Problems Implementation Aspects and CPU-Time and Memory Scalings.- 2-D Axisymmetric Line Transport.- NLTE Spectral Line Formation in Three Dimensions.- Iteration with Approximate Lambda Operators, and its Application to the Expanding Atmospheres of WR Stars.- Analytical Methods of Line Formation Theory: Are They Still Alive?.- Iteration Factors in the Solution of the NLTE Line Transfer Problem.- Analysis of Ultraviolet P Cygni Profiles in the Spectra of O-Type Stars.- Computer Codes for Stellar Atmospheric Modeling.- Section 2..- The Quest for Physical Realism in Stellar Atmospheric Modeling.- Unified NLTE Model Atmospheres Including Spherical Extension and Stellar Winds: Euv-Fluxes and the HE II Discrepancy in Central Stars of Planetary Nebulae.- Non-LTE Model Atmosphere Calculations with Approximate Lambda Operators.- NLTE Model Atmospheres for Hot Stars.- Radiative Transfer in Expanding Atmospheres - Radiative Acceleration of Wolf-Rayet Envelopes?.- Non-LTE Analysis of Hot Stars Including Line Blanketing.- Time-Dependent Two-Dimensional Radiation Hydrodynamics of Accreting Matter onto Highly Magnetized Neutron Stars: The Evolution of Photon Bubbles.- The Origin and Development of Instabilities in Radiatively- Driven Stellar Winds.- A Smooth Source Function Method for Including Scattering in Radiatively Driven Wind Simulations.- 2-D Radiation Hydrodynamics Models of the Solar Photosphere.- Dynamics of and Radiative Transfer in Inhomogeneous Media.- Atmospheres of Late-Type Giants.- Fe II Emission Line Diagnostics of the Sun and Stars.- Chromospheric Inhomogeneities in Cool Stars: Possible Effect on Hydrogen Line Profiles.- Numerical Simulation of Photospheric Convection: Hydrodynamical Test Calculations.- Section 3..- Stellar Atmosphere Theory as a Spectroscopic Tool. The Example of Hot Stars.- The Winds of O-Stars. V: Tests of the Accuracy of the Radiation Driven Wind Models.- Diagnostics of Wolf-Rayet Atmospheres.- Central Stars of PN: Spectral Diagnostics Based on Model Atmospheres VS. Diagnostics Based on the Classical Nebular Approach.- Spectral Diagnostics of Hot Subdwarfs: Successes and Problems.- Temperatures, Gravities and Abundances of B Stars: Recent Progress and Remaining Problems.- Line Blanketing Without LTE: The Effect on Diagnostics for B-Type Stars.- Particle Transport in Magnetic Stellar Atmospheres.- Spectroscopic Tests of Late-Type Model Atmospheres of Dwarf Stars.- Dust in the Shells of Cool Giants and Supergiants.- NLTE Analysis of Massive OB Stars.- Formation of the K I 7699 A Line in Sunspots.- On the Influence of Multi-Dimensional Radiative Transfer on the Energetic Contribution of the Ca K Line.- Special Session.- The Opacity Project and the Practical Utilization of Atomic Data.- New Opacity Calculations.- 40 Years Numerical Stellar Atmospheres: Concluding Remarks and Personal Considerations.

Stellar Atmospheres: Beyond Classical Models

The redistribution in frequency of radiation scattered from moving atoms is examined in some generality, allowing for the different types of scattering that occur in the atom's rest frame under different circumstances. Some general formulas are obtained and a number of explicit results are given. Finally some attention is devoted to the properties of the redistribution functions and to the methods that may be used for computing them. (auth)

/pdf/non-coherent-scattering-i-the-redistribution-function-with-2ouslfpset.pdf

D. G. Hummer

Papers

Recombination-line intensities for hydrogenic ions – I. Case B calculations for H I and He II

The equation of state for stellar envelopes. I - An occupation probability formalism for the truncation of internal partition functions

The equation of state for stellar envelopes. II - Algorithm and selected results

Stellar Atmospheres: Beyond Classical Models

Non-Coherent Scattering: I. The Redistribution Function with Doppler Broadening