Special Issue "Atomic and Molecular Opacity Data for Astrophysics"

A special issue of Atoms (ISSN 2218-2004).

Deadline for manuscript submissions: closed (31 March 2018)

Special Issue Editor

Guest Editor
Dr. Jean-Christophe Pain

Commissariat à l’Energie Atomique (CEA), DAM, DIF, F-91297 Arpajon, France
E-Mail
Interests: helio- and asteroseismology; stellar spectra; multicharged-ion plasmas; local and non-local thermodynamic equilibrium plasmas; radiative opacity; atomic processes in stellar interiors and envelopes; photo-ionization; photo-excitation; inverse Bremsstrahlung; databases; radiative transfer; radiative acceleration; molecular opacity

Special Issue Information

Dear Colleagues,

The revision of the standard Los Alamos opacities thirty years ago by the Lawrence Livermore National Laboratory (OPAL) and the Opacity Project (OP) teams was an early example of collaborative big-data science, yielding reliable computed quantities (spectral and mean opacities, radiative accelerations) that were widely used to investigate many astrophysical topics. The precision of the calculated opacities is a key point of comparisons between theory, laboratory (laser or Z-pinch) plasma spectroscopy experiments, and stellar observations in different frameworks: Standard Solar Model (SSM); helio- and astero-seismology (for instance of Beta Cephei-type pulsating stars); non-local thermodynamic-equilibrium 3D hydrodynamic photospheric modeling; nuclear reaction rates, solar neutrino detections, etc. In this context, the recent revision of the solar photospheric metal abundances in 2005 spoiled the agreement between the helioseismic indicators (depth of the convection zone, sound-speed profile, and helium surface abundance) and the SSM predictions, agreement that could be recovered with a substantial opacity increase.

Spectroscopic observations of brown dwarfs and extrasolar giant planets (hot Jupiter stars and super-Earths) in the infrared to the ultraviolet ranges are now possible. The model atmospheres can be tested for atmospheric temperatures (100–3000 K) and pressures (10-6–100 atm) at which many molecules reside. Molecular opacities (accounting for rotational-vibrational and electronic bound-free, bound-bound, free-free, and collision-induced transitions) for alkali metals, iron, heavy metal oxides, metal hydrides, H2, CO, H2O, N2, CH4, NH3, CO2, HCN, H2S, PH3, etc., needed to simulate astronomical observations, can be obtained from laboratory measurements or ab initio calculations.

This Special Issue of Atoms will highlight the need for continuing research on the atomic and molecular opacity data for astrophysics. It will present recent theoretical and experimental works, as well as investigations in astrophysics where opacities have been used as a tool to investigate physical properties of celestial objects.

Dr. Jean-Christophe Pain
Guest Editor

Manuscript Submission Information

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Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 350 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • stellar spectra
  • Active-Galactic-Nuclei spectra
  • interstellar spectra
  • asteroseismology
  • pulsating stars
  • beta Cephei
  • Standard Solar Model
  • tachocline
  • exoplanets
  • extragalactic objects
  • laboratory plasma
  • Z-pinch
  • lasers
  • atomic and molecular opacity

Published Papers (6 papers)

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Research

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Open AccessFeature PaperArticle A New Implementation of the STA Method for the Calculation of Opacities of Local Thermodynamic Equilibrium Plasmas
Received: 10 April 2018 / Revised: 15 June 2018 / Accepted: 15 June 2018 / Published: 21 June 2018
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Abstract
We present opacity calculations with the newly developed STAR code, which implements the Super-Transition-Array (STA), with various improvements. The model is used to calculate and analyze local thermodynamic equilibrium opacities of mid and high Z elements and of the solar interior plasma. We
[...] Read more.
We present opacity calculations with the newly developed STAR code, which implements the Super-Transition-Array (STA), with various improvements. The model is used to calculate and analyze local thermodynamic equilibrium opacities of mid and high Z elements and of the solar interior plasma. We briefly review the underlying computational model and present calculations for iron and neodymium over a wide range of temperature and density. Full article
(This article belongs to the Special Issue Atomic and Molecular Opacity Data for Astrophysics)
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Open AccessFeature PaperArticle New Los Alamos Opacity Calculations
Received: 5 April 2018 / Revised: 2 May 2018 / Accepted: 3 May 2018 / Published: 4 June 2018
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Abstract
In 2015 Los Alamos National Laboratory (LANL) released a new set of OPLIB opacity tables for the elements hydrogen through zinc. The new LANL opacities are publicly available via our website and are already in use by the astrophysics community. In this contribution,
[...] Read more.
In 2015 Los Alamos National Laboratory (LANL) released a new set of OPLIB opacity tables for the elements hydrogen through zinc. The new LANL opacities are publicly available via our website and are already in use by the astrophysics community. In this contribution, we discuss the extension of our opacity calculations to elements beyond zinc. Such calculations are motivated by potential industrial applications (for elements such as Sn) as well as available experimental data with which to compare our calculations (for Ge and Br). After a short outline of our method for computing opacities for these elements, we make comparisons to available experimental data and find good agreement. Future plans are briefly discussed. Full article
(This article belongs to the Special Issue Atomic and Molecular Opacity Data for Astrophysics)
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Open AccessFeature PaperArticle Opacity Effects on Pulsations of Main-Sequence A-Type Stars
Received: 10 April 2018 / Revised: 10 May 2018 / Accepted: 11 May 2018 / Published: 4 June 2018
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Abstract
Opacity enhancements for stellar interior conditions have been explored to explain observed pulsation frequencies and to extend the pulsation instability region for B-type main-sequence variable stars. For these stars, the pulsations are driven in the region of the opacity bump of Fe-group elements
[...] Read more.
Opacity enhancements for stellar interior conditions have been explored to explain observed pulsation frequencies and to extend the pulsation instability region for B-type main-sequence variable stars. For these stars, the pulsations are driven in the region of the opacity bump of Fe-group elements at ∼200,000 K in the stellar envelope. Here we explore effects of opacity enhancements for the somewhat cooler main-sequence A-type stars, in which p-mode pulsations are driven instead in the second helium ionization region at ∼50,000 K. We compare models using the new LANL OPLIB vs. LLNL OPAL opacities for the AGSS09 solar mixture. For models of two solar masses and effective temperature 7600 K, opacity enhancements have only a mild effect on pulsations, shifting mode frequencies and/or slightly changing kinetic-energy growth rates. Increased opacity near the bump at 200,000 K can induce convection that may alter composition gradients created by diffusive settling and radiative levitation. Opacity increases around the hydrogen and 1st He ionization region (∼13,000 K) can cause additional higher-frequency p modes to be excited, raising the possibility that improved treatment of these layers may result in prediction of new modes that could be tested by observations. New or wider convective zones and higher convective velocities produced by opacity increases could also affect angular momentum transport during evolution. More work needs to be done to quantify the effects of opacity on the boundaries of the pulsation instability regions for A-type stars. Full article
(This article belongs to the Special Issue Atomic and Molecular Opacity Data for Astrophysics)
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Open AccessFeature PaperArticle The ExoMol Atlas of Molecular Opacities
Received: 25 February 2018 / Revised: 3 May 2018 / Accepted: 4 May 2018 / Published: 10 May 2018
Cited by 2 | PDF Full-text (5828 KB) | HTML Full-text | XML Full-text
Abstract
The ExoMol project is dedicated to providing molecular line lists for exoplanet and other hot atmospheres. The ExoMol procedure uses a mixture of ab initio calculations and available laboratory data. The actual line lists are generated using variational nuclear motion calculations. These line
[...] Read more.
The ExoMol project is dedicated to providing molecular line lists for exoplanet and other hot atmospheres. The ExoMol procedure uses a mixture of ab initio calculations and available laboratory data. The actual line lists are generated using variational nuclear motion calculations. These line lists form the input for opacity models for cool stars and brown dwarfs as well as for radiative transport models involving exoplanets. This paper is a collection of molecular opacities for 52 molecules (130 isotopologues) at two reference temperatures, 300 K and 2000 K, using line lists from the ExoMol database. So far, ExoMol line lists have been generated for about 30 key molecular species. Other line lists are taken from external sources or from our work predating the ExoMol project. An overview of the line lists generated by ExoMol thus far is presented and used to evaluate further molecular data needs. Other line lists are also considered. The requirement for completeness within a line list is emphasized and needs for further line lists discussed. Full article
(This article belongs to the Special Issue Atomic and Molecular Opacity Data for Astrophysics)
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Open AccessFeature PaperArticle Detailed Opacity Calculations for Astrophysical Applications
Received: 30 January 2017 / Revised: 2 May 2017 / Accepted: 16 May 2017 / Published: 30 May 2017
Cited by 1 | PDF Full-text (4718 KB) | HTML Full-text | XML Full-text
Abstract
Nowadays, several opacity codes are able to provide data for stellar structure models, but the computed opacities may show significant differences. In this work, we present state-of-the-art precise spectral opacity calculations, illustrated by stellar applications. The essential role of laboratory experiments to check
[...] Read more.
Nowadays, several opacity codes are able to provide data for stellar structure models, but the computed opacities may show significant differences. In this work, we present state-of-the-art precise spectral opacity calculations, illustrated by stellar applications. The essential role of laboratory experiments to check the quality of the computed data is underlined. We review some X-ray and XUV laser and Z-pinch photo-absorption measurements as well as X-ray emission spectroscopy experiments involving hot dense plasmas produced by ultra-high-intensity laser irradiation. The measured spectra are systematically compared with the fine-structure opacity code SCO-RCG. The focus is on iron, due to its crucial role in understanding asteroseismic observations of β Cephei-type and Slowly Pulsating B stars, as well as of the Sun. For instance, in β Cephei-type stars, the iron-group opacity peak excites acoustic modes through the “kappa-mechanism”. Particular attention is paid to the higher-than-predicted iron opacity measured at the Sandia Z-machine at solar interior conditions. We discuss some theoretical aspects such as density effects, photo-ionization, autoionization or the “filling-the-gap” effect of highly excited states. Full article
(This article belongs to the Special Issue Atomic and Molecular Opacity Data for Astrophysics)
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Review

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Open AccessFeature PaperReview Computation of Atomic Astrophysical Opacities
Received: 26 February 2018 / Revised: 9 May 2018 / Accepted: 9 May 2018 / Published: 18 May 2018
PDF Full-text (963 KB) | HTML Full-text | XML Full-text
Abstract
The revision of the standard Los Alamos opacities in the 1980–1990s by a group from the Lawrence Livermore National Laboratory (OPAL) and the Opacity Project (OP) consortium was an early example of collaborative big-data science, leading to reliable data deliverables (atomic databases, monochromatic
[...] Read more.
The revision of the standard Los Alamos opacities in the 1980–1990s by a group from the Lawrence Livermore National Laboratory (OPAL) and the Opacity Project (OP) consortium was an early example of collaborative big-data science, leading to reliable data deliverables (atomic databases, monochromatic opacities, mean opacities, and radiative accelerations) widely used since then to solve a variety of important astrophysical problems. Nowadays the precision of the OPAL and OP opacities, and even of new tables (OPLIB) by Los Alamos, is a recurrent topic in a hot debate involving stringent comparisons between theory, laboratory experiments, and solar and stellar observations in sophisticated research fields: the standard solar model (SSM), helio and asteroseismology, non-LTE 3D hydrodynamic photospheric modeling, nuclear reaction rates, solar neutrino observations, computational atomic physics, and plasma experiments. In this context, an unexpected downward revision of the solar photospheric metal abundances in 2005 spoiled a very precise agreement between the helioseismic indicators (the radius of the convection zone boundary, the sound-speed profile, and helium surface abundance) and SSM benchmarks, which could be somehow reestablished with a substantial opacity increase. Recent laboratory measurements of the iron opacity in physical conditions similar to the boundary of the solar convection zone have indeed predicted significant increases (30–400%), although new systematic improvements and comparisons of the computed tables have not yet been able to reproduce them. We give an overview of this controversy, and within the OP approach, discuss some of the theoretical shortcomings that could be impairing a more complete and accurate opacity accounting. Full article
(This article belongs to the Special Issue Atomic and Molecular Opacity Data for Astrophysics)
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