Spectral line shapes modeling in laboratory and astrophysical plasmas (original) (raw)
Related papers
Laser-plasma and stellar astrophysics spectroscopy
Contributions of the Astronomical Observatory Skalnaté Pleso
This work examines time-resolved spectroscopy of the Balmer series lines in laboratory settings and applies results for interpretation of spectra from astrophysical objects. White dwarf stars reveal a variety of atomic or molecular line shapes in absorption depending on the age of these cooling stars. Laboratory investigations show emission profiles that are correlated with astrophysical records. For the hydrogen beta line, Hβ, and the hydrogen delta line, Hδ, of the Balmer series, line width and peak separation are indicators of electron density. In addition, widths of the hydrogen alpha line, Hα, and hydrogen gamma line, Hγ, can be utilized along with Hα shifts and Hβ dipshifts. Of interest are experiments and analysis of laser-and astrophysical white-dwarfplasma spectral line shapes, especially comparisons of transient laser-plasmawith gravitational white-dwarf-redshifts. Current and future research aspects include modeling of white-dwarf atmospheres for explanation of the very details of the astrophysical line shapes.
Laboratory Hydrogen-Beta Emission Spectroscopy for Analysis of Astrophysical White Dwarf Spectra
Atoms, 2018
This work communicates a review on Balmer series hydrogen beta line measurements and applications for analysis of white dwarf stars. Laser-induced plasma investigations explore electron density and temperature ranges comparable to white dwarf star signatures such as Sirius B, the companion to the brightest star observable from the earth. Spectral line shape characteristics of the hydrogen beta line include width, peak separation, and central dip-shift, thereby providing three indicators for electron density measurements. The hydrogen alpha line shows two primary line-profile parameters for electron density determination, namely, width and shift. Both Boltzmann plot and line-to-continuum ratios yield temperature. The line-shifts recorded with temporally-and spatially-resolved optical emission spectroscopy of hydrogen plasma in laboratory settings can be larger than gravitational redshifts that occur in absorption spectra from radiating white dwarfs. Published astrophysical spectra display significantly diminished Stark or pressure broadening contributions to red-shifted atomic lines. Gravitational redshifts allow one to assess the ratio of mass and radius of these stars, and, subsequently, the mass from cooling models.
Simulation of Stark-broadened Hydrogen Balmer-line Shapes for DA White Dwarf Synthetic Spectra
The Astrophysical Journal, 2022
White dwarfs (WDs) are useful across a wide range of astrophysical contexts. The appropriate interpretation of their spectra relies on the accuracy of WD atmosphere models. One essential ingredient of atmosphere models is the theory used for the broadening of spectral lines. To date, the models have relied on Vidal et al., known as the unified theory of line broadening (VCS). There have since been advancements in the theory; however, the calculations used in model atmosphere codes have only received minor updates. Meanwhile, advances in instrumentation and data have uncovered indications of inaccuracies: spectroscopic temperatures are roughly 10% higher and spectroscopic masses are roughly 0.1 M ⊙ higher than their photometric counterparts. The evidence suggests that VCS-based treatments of line profiles may be at least partly responsible. Gomez et al. developed a simulation-based line-profile code Xenomorph using an improved theoretical treatment that can be used to inform question...
Atoms
This work discusses laboratory measurements of atomic and diatomic molecular species in laser-plasma generated in gases. Noticeable self-absorption of the Balmer series hydrogen alpha line occurs for electron densities of the order of one tenth of standard ambient temperature and pressure density. Emission spectra of selected diatomic molecules in air or specific gaseous mixtures at or near atmospheric pressure reveal minimal plasma re-absorption. Abel inversion of the plasma in selected gases and gas mixtures confirm expansion dynamics that unravel regions of atomic and molecular species of different electron temperature and density. Time resolved spectroscopy diagnoses self-absorption of hydrogen alpha and hydrogen beta lines in ultra-high pure hydrogen gas. Radiation from a Nd:YAG laser device induces micro-plasma for pulse widths in the range of 6–14 ns, energies in the range of 100–800 mJ, and peak irradiances of the order 1–10 TW/cm 2 . Atomic line profiles yield electron dens...
Laboratory Measurements of White Dwarf Photospheric Spectral Lines: H Β
The Astrophysical Journal, 2015
We spectroscopically measure multiple hydrogen Balmer line profiles from laboratory plasmas to investigate the theoretical line profiles used in white dwarf atmosphere models. X-ray radiation produced at the Z Pulsed Power Facility at Sandia National Laboratories initiates plasma formation in a hydrogen-filled gas cell, replicating white dwarf photospheric conditions. Here we present timeresolved measurements of Hβ and fit this line using different theoretical line profiles to diagnose electron density, n e , and n = 2 level population, n 2. Aided by synthetic tests, we characterize the validity of our diagnostic method for this experimental platform. During a single experiment, we infer a continuous range of electron densities increasing from n e ∼ 4 to ∼ 30 × 10 16 cm −3 throughout a 120-ns evolution of our plasma. Also, we observe n 2 to be initially elevated with respect to local thermodynamic equilibrium (LTE); it then equilibrates within ∼ 55 ns to become consistent with LTE. This supports our electron-temperature determination of T e ∼ 1.3 eV (∼ 15, 000 K) after this time. At n e 10 17 cm −3 , we find that computer-simulation-based line-profile calculations provide better fits (lower reduced χ 2) than the line profiles currently used in the white dwarf astronomy community. The inferred conditions, however, are in good quantitative agreement. This work establishes an experimental foundation for the future investigation of relative shapes and strengths between different hydrogen Balmer lines.
Monthly Notices of the Royal Astronomical Society, 2015
Recently an accurate analysis of absorption spectra of molecular hydrogen, observed with the Cosmic Origins Spectrograph aboard the Hubble Space Telescope, in the photosphere of white dwarf stars GD133 and GD29-38 was published in a Letter [Phys. Rev. Lett. 113, 123002 (2014)], yielding a constraint on a possible dependence of the proton-electron mass ratio on a gravitational field of strength 10,000 times that at the Earth's surface. In the present paper further details of that study are presented, in particular a re-evaluation of the spectrum of the B 1 Σ + u − X 1 Σ + g (v ′ , v ′′) Lyman bands relevant for the prevailing temperatures (12,000-14,000 K) of the photospheres. An emphasis is on the calculation of so-called K i-coefficients, that represent the sensitivity of each individual line to a possible change in the proton-electron mass ratio. Such calculations were performed by semi-empirical methods and by ab initio methods providing accurate and consistent values. A full listing is provided for the molecular physics data on the Lyman bands (wavelengths λ i , line oscillator strengths f i , radiative damping rates Γ i , and sensitivity coefficients K i) as required for the analyses of H 2-spectra in hot dwarf stars. A similar listing of the molecular physics parameters for the C 1 Π u − X 1 Σ + g (v ′ , v ′′) Werner bands is provided for future use in the analysis of white dwarf spectra.
Hydrogen Line Shape Uncertainties in White Dwarf Model Atmospheres
Frontiers in Astronomy and Space Sciences, 2022
For isolated white dwarf (WD) stars, fits to their observed spectra provide the most precise estimates of their effective temperatures and surface gravities. Even so, recent studies have shown that systematic offsets exist between such spectroscopic parameter determinations and those based on broadband photometry. These large discrepancies (10% inTeff, 0.1 M⊙in mass) provide scientific motivation for reconsidering the atomic physics employed in the model atmospheres of these stars. Recent simulation work of ours suggests that the most important remaining uncertainties in simulation-based calculations of line shapes are the treatment of 1) the electric field distribution and 2) the occupation probability (OP) prescription. We review the work that has been done in these areas and outline possible avenues for progress.
Examples of spectroscopy of laboratory plasma with possible connection to astrophysical plasmas
New Astronomy Reviews, 2009
In this paper several examples of line spectra from five different laboratory plasma sources are presented. Polarization Stark spectroscopy using hydrogen and helium lines is used for measuring electric field strength in the discharge. Doppler shifted and excessively broadened profiles are obtained showing presence of atoms with velocities close to those in the narrow line region of AGN. Radiation from a high energy, high density plasma source features very broad profiles used for determination of plasma density. Careful interpretation of spectra is needed in the conditions where several effects are present simultaneously: electric and magnetic field, Doppler effect and plasma inhomogeneity. Examples of line of sight influence on profile are also presented. Similarity between laboratory and astrophysical profiles open a possible field for experimental simulation of astrophysical plasmas.
On Asymmetry of Hydrogen Spectral Lines in Nonequlibrium Plasmas
2008
The Standard Theory (ST) of hydrogen spectral lines Stark broadening is applied within many-body approach to detailed description of profile asymmetry simultaneously accounting for the quadrupole interaction, quadratic Stark effect shifts and corrections to oscillator strengths. The influence of electronic collision shifts and impact widths, trivial asymmetry, the Boltzmann and dipole intensity scaling factors are studied as well. The consistent inclusion of the latter two factors in ST frames requests the line contour redefinition to avoid divergence. It is demonstrated that the asymmetry of hydrogen spectral lines is the many-parametric sensitive function of broadening mechanisms. The comparison with the precision experiment on stabilized arc data for Hjg line has shown good coincidence within assumption of nonequilibrium between electrons and heavy neutral particles.
Stark broadening effect in hot DA white dwarfs: Ultraviolet lines of Fe V
Astronomische Nachrichten, 2021
Stark widths and shifts have been calculated for 17 ultraviolet lines of Fe V of astrophysical interest. The calculations have been made using semiclassical perturbation approach. The work is motivated by the importance of ultraviolet lines for the study of hot white dwarf atmospheres specially for investigations of the variation of fine structure constant in strong gravitational field. Our Stark broadening parameters are presented for a range of temperature from 50,000 to 600,000 K. Our results are used to investigate the importance of electron impact broadening in plasma conditions of hot DA white dwarfs. Electron impact Stark width is compared to Doppler width as a function of atmospheric layer temperature and as a function of logarithm of Rosseland optical depth.