Low-density Astrophysical Plasmas Research Articles

New Ritz wavelengths and transition probabilities for parity-forbidden, singly ionized nickel [Ni ii] lines of astrophysical interest

ABSTRACT We report accurate Ritz wavelengths for parity-forbidden [Ni ii] transitions, derived from energy levels determined using high-resolution Fourier transform spectroscopy. Transitions between the 18 lowest Ni ii energy levels of even-parity produced Ritz wavelengths for 126 parity-forbidden lines. Uncertainties for the Ritz wavelengths derived in this work are up to two orders of magnitude lower than previously published values. Transition probabilities were calculated using the semi-empirical orthogonal operator method, with uncertainties ranging from approximately 1 per cent for strong M1 lines and up to 10 per cent for weak E2 lines. Accurate forbidden line wavelengths and transition probabilities, particularly for lines in the infrared, are important in the analyses of low-density astrophysical plasmas, such as supernova remnants, planetary nebulae, and active galactic nuclei.

Recombination of Hot Ionized Nebulae: The Old Planetary Nebula around V4334 Sgr (Sakurai’s Star)* * This investigation makes use of ESO data from program IDs 077.D-0394, 079.D-0256, 381.D-0117, 383.D-0427, 385.D-0292, 087.D-0223, 089.D-0080, 091.D-0209, 093.D-0195, 095.D-0113, 097.D-0146, 099.D-0045, and 0109.D-0060.

After becoming ionized, low-density astrophysical plasmas will begin a process of slow recombination. Models for this still have significant uncertainties. Recombination cannot normally be observed in isolation, because the ionization follows the evolutionary timescale of the ionizing source. Laboratory experiments are unable to reach the appropriate conditions because of the very long required timescales. The extended nebula around the very late helium pulse (VLTP) star V4334 Sgr provides a unique laboratory for this kind of study. The sudden loss of the ionizing UV radiation after the VLTP event has allowed the nebula to recombine free from other influences. More than 290 long-slit spectra taken with FORS1/2 at ESO’s Very Large Telescope between 2007 and 2022 are used to follow the time evolution of the lines of H, He, N, S, O, and Ar. Hydrogen and helium lines, representing most of the ionized mass, do not show significant changes. A small increase is seen in [N ii] (+2.8% yr−1; 2.7σ significance), while we see a decrease in [O iii] (−1.96% yr−1; 2.0σ significance). The [S ii] lines show a change of +3.0% yr−1 (1.6σ significance). The lines of [S iii] and of [Ar iii] show no significant changes. For [S iii], the measurement differs from the predicted decrease by 4.5σ. A possible explanation is that the fractions of S3+ and higher are larger than expected. Such an effect could provide a potential solution for the sulfur anomaly in planetary nebulae.

Direct observations of anomalous resistivity and diffusion in collisionless plasma

Coulomb collisions provide plasma resistivity and diffusion but in many low-density astrophysical plasmas such collisions between particles are extremely rare. Scattering of particles by electromagnetic waves can lower the plasma conductivity. Such anomalous resistivity due to wave-particle interactions could be crucial to many processes, including magnetic reconnection. It has been suggested that waves provide both diffusion and resistivity, which can support the reconnection electric field, but this requires direct observation to confirm. Here, we directly quantify anomalous resistivity, viscosity, and cross-field electron diffusion associated with lower hybrid waves using measurements from the four Magnetospheric Multiscale (MMS) spacecraft. We show that anomalous resistivity is approximately balanced by anomalous viscosity, and thus the waves do not contribute to the reconnection electric field. However, the waves do produce an anomalous electron drift and diffusion across the current layer associated with magnetic reconnection. This leads to relaxation of density gradients at timescales of order the ion cyclotron period, and hence modifies the reconnection process.

New Ritz Wavelengths and Transition Probabilities of Parity-forbidden [Mn II] Lines of Astrophysical Interest.

We report a comprehensive list of accurate Ritz wavelengths and calculated transition probabilities for parity-forbidden [Mn II] lines. Ritz wavelengths have been derived from experimentally established energy level values resulting from an extensive analysis of a high-resolution Fourier-transform emission spectrum of singly ionized manganese. Our analysis includes transitions between all known metastable and other long-lived levels of Mn II giving a total of 1130 [Mn II] Ritz wavelengths. Our entire list of derived Ritz wavelengths for [Mn II] lines ranges between 237 nm and 170 μm (42,125-58 cm-1). The accurate Ritz wavelengths and calculated transition probabilities for forbidden lines in this paper are useful in the study and diagnostics of nebulae and other low-density astrophysical plasmas.

Dielectronic satellite lines of Fe XVII

We have been measuring the L-shell x-ray emission produced by dielectronic recombination of neonlike Fe16+ ions populating doubly excitated levels of the form 1s22l73ℓn'ℓ' in Fe15+. The measurements are carried out at the Livermore electron beam ion trap facility, where we isolate dielectronic resonances by choice of the electron beam energy. We utilize crystal spectrometers to record the x-ray lines generated in the radiative deexcitation of the 1s22l73ℓn'ℓ' upper levels. The measurements aim to support the identification of such lines in low-density astrophysical plasmas.

ACCURATE RITZ WAVELENGTHS OF PARITY-FORBIDDEN [Co II] AND [V II] LINES OF ASTROPHYSICAL INTEREST

We report a comprehensive list of accurate Ritz wavelengths for parity-forbidden [Co II] and [V II] lines obtained from the analysis of energy levels measured in the laboratory with Fourier transform emission spectroscopy. Such lines, particularly those in the infrared, are in demand for the analysis of low-density astrophysical plasmas in and around objects such as planetary nebulae, star-forming regions, and active galactic nuclei. Transitions between all known metastable levels of Co II and V II are included in our analysis, producing wavelengths for 1477 [V II] lines and 782 [Co II] lines. Of these, 170 [V II] lines and 171 [Co II] lines arise from transitions with calculated transition probabilities greater than 1 × 10–2 s–1 and upper level excitations of less than 5 eV, and thus are likely to be observed in astrophysical spectra.

INTERMITTENT HEATING IN SOLAR WIND AND KINETIC SIMULATIONS

Low-density astrophysical plasmas may be described by magnetohydrodynamics at large scales, but require kinetic description at ion scales in order to include dissipative processes that terminate the cascade. Here kinetic plasma simulations and high-resolution spacecraft observations are compared to facilitate the interpretation of signatures of various dissipation mechanisms. Kurtosis of increments indicates that kinetic scale coherent structures are present, with some suggestion of incoherent activity near ion scales. Conditioned proton temperature distributions suggest heating associated with coherent structures. The results reinforce the association of intermittent turbulence, coherent structures, and plasma dissipation.

Atomic physics and ionization balance of high-Z Ions: Critical ingredients for characterizing and understanding high-temperature plasmas

A correct description of the ionization balance of high-Z ions, i.e., the fractional abundance of different charge states of a particular element, is critical for interpreting diagnostic line ratios, for describing radiation flow within and out of the plasma, and for assessing the energy balance of high-temperature plasmas. Despite the fundamental nature of this atomic physics parameter, the ionization balance as a function of plasma electron density and electron temperature is generally rather poorly known both experimentally and theoretically. This is the case irregardless of the type of plasma, i.e., low-density astrophysical and coronal plasmas, intermediate density magnetically confined fusion plasmas, or high energy density (HED) laboratory plasmas. We illustrate these points by reviewing existing measurements of the ionization balance of high-Z elements in high-temperature plasmas and discussing the difficulties associated with ionization balance calculations. We focus on the two high-Z elements tungsten (Z=74) and gold (Z=79), which play important roles in magnetic fusion and HED plasmas and for which we present calculations of the ionization energies for each charge state. We show that the accuracy of the treatment of dielectronic recombination is currently a limiting factor in proper modeling of the ionization balance and propose “differential” measurements that determine the amount of dielectronic recombination concurrently with the ionization balance as the next step for advancing ionization balance modeling. As an example of the differential measurement approach, we present recent experiments carried out at the Livermore electron beam ion trap, which investigated the ionization balance of gold in the presence of beam-resonant dielectronic recombination. These plasmas limit the immense complexity of dielectronic recombination resonances so that both approximate and reasonably complete detailed calculations can be compared to the measurements. This represents a path forward for constructing and selecting those approximations that produce the most reliable ionization balance models.

NUCLEAR REACTIONS IN HOT ASTROPHYSICAL PLASMAS WITH T > 1010 K

The importance of nuclear reactions in low-density astrophysical plasmas with ion temperatures T ≥1010 K has been recognized for more than thirty years. However, the lack of comprehensive data banks of relevant nuclear reactions and the limited computational power have not previously allowed detailed theoretical studies. Recent developments in these areas make it timely to conduct comprehensive studies on the nuclear properties of very hot plasmas formed around compact relativistic objects such as black holes and neutron stars. Such studies are of great interest in the context of scientific programs of future low-energy cosmic γ-ray spectrometry. In this work, using the publicly available code TALYS, we have built a large nuclear network relevant for temperatures exceeding 1010 K. We have studied the evolution of the chemical composition and accompanying prompt gamma-ray emission of such high-temperature plasmas. We present the results on the abundances of light elements D, T, 3 He , 4 He , 6 Li , 7 Li , 9 Be , 10 B , 11 B , and briefly discuss their implications on the astrophysical abundances of these elements.

The FERRUM project: metastable lifetimes in Cr ii

Parity forbidden radiative transitions from metastable levels are observed in spectra of low-density astrophysical plasmas. These lines are used as probes of the physical conditions, made possible due to the long lifetime of their upper level. In a joint effort, the FERRUM project aims to obtain new and accurate atomic data for the iron-group elements, and part of this project concerns forbidden lines. The radiative lifetimes of the metastable energy levels 3 d4(a 3 D)4 s c4 D 5/2 and 3 d4(a 3 D)4 s c4 D 7/2 of singly ionized chromium have been measured. The experiment has been performed at the ion storage ring CRYRING. We employed a laser-probing technique developed for measuring long lifetimes. In this article, we present the lifetimes of these levels to be t5/2= 1.28(16) s and t7/2= 1.37(7) s, respectively. A comparison with previous theoretical work shows good agreement and the result is discussed in a theoretical context.

Prediction of CME as an inverse problem

Magnetic reconnection has been invoked as the energy release mechanism for solar flares and coronal mass ejections release from the sun's lower atmosphere. Theoretical models of magnetic reconnection have been traditionally developed within the frame work of magneto-hydrodynamics. However, in low density astrophysical plasmas such as in solar atmosphere, kinetic effects are expected to play a significant role. Here we have developed a kinematic theory for the prediction of CME which is a novel approach. Based on our data analysis we have assumed a general quadratic expression for the distribution function in velocity space and have looked for the complete class of self consistent magnetic fields, potential fields as well as density distributions. In our problem the occurrence of the complex roots reveal the existence of instability which can be interpreted as the CME.

The FERRUM project: transition probabilities for forbidden lines in [Fe II] and experimental metastable lifetimes

Accurate transition probabilities for forbidden lines are important diagnostic parameters for low-density astrophysical plasmas. In this paper we present experimental atomic data for forbidden [FeII] transitions that are observed as strong features in astrophysical spectra. Aims: To measure lifetimes for the 3d^6(^3G)4s a ^4G_{11/2} and 3d^6(^3D)4s b ^4D_{1/2} metastable levels in FeII and experimental transition probabilities for the forbidden transitions 3d^7 a ^4F_{7/2,9/2}- 3d^6(^3G)4s a ^4G_{11/2}. Methods: The lifetimes were measured at the ion storage ring facility CRYRING using a laser probing technique. Astrophysical branching fractions were obtained from spectra of Eta Carinae, obtained with the Space Telescope Imaging Spectrograph onboard the Hubble Space Telescope. The lifetimes and branching fractions were combined to yield absolute transition probabilities. Results: The lifetimes of the a ^4G_{11/2} and the b ^4D_{1/2} levels have been measured and have the following values, 0.75(10) s and 0.54(3) s respectively. Furthermore, we have determined the transition probabilities for two forbidden transitions of a ^4F_{7/2,9/2}- a ^4G_{11/2} at 4243.97 and 4346.85 A. Both the lifetimes and the transition probabilities are compared to calculated values in the literature.

Accurate Ritz wavelengths of parity-forbidden [$\ion{Fe}{ii}$], [$\ion{Ti}{ii}$], and [$\ion{Cr}{ii}$] infrared lines of astrophysical interest

Context.With new astronomical infrared spectrographs the demands of accurate atomic data in the infrared have increased. In this region there is a large amount of parity-forbidden lines, which are of importance in diagnostics of low-density astrophysical plasmas.

Electron-impact rotational excitation of : relevance for thermalization and dissociation dynamics

Electrons are known to be efficient in rotationally exciting molecular ions in low-density astrophysical plasmas. Rotational excitation of molecular ions has also been shown to affect the measured values of dissociative recombination (DR) rate coefficients. Thus, electron collisions with H3+ are expected to play a significant role in thermalization and dissociation dynamics of this ion, both in the laboratory and in space. Using the molecular R-matrix method combined with the adiabatic-nuclei-rotation approximation, we have computed new rate coefficients for the rotational excitation of H3+ by electrons at temperatures from 10 to 10,000 K. De-excitation rates are found to amount to a few 10(-7) cm3 s(-1) below 1000 K, i.e. comparable in magnitude to that of DR. In astrophysical environments where the electron fraction exceeds 10(-4), electron collisions are thus expected to contribute to the non-thermal rotational distribution of H3+. The competition between electron and neutral collisions is discussed in the context of recent observations of H3+ towards Galactic centre sources.

The role of Hall currents on incompressible magnetic reconnection

Magnetic reconnection is one of the most important energy conversion processes in space plasmas. Theoretical models of magnetic reconnection have been traditionally developed within the framework of magnetohydrodynamics (MHD). However, in low density astrophysical plasmas as those found in the magnetopause and the magnetotail, the current sheet thickness can be comparable to the ion inertial scale and therefore the Hall electric field becomes non-negligible. The role of the Hall current is to increase the reconnection rate with respect to MHD predictions, which therefore poses a promising mechanism for fast reconnection. We present results from parallel simulations of the incompressible Hall MHD equations in 2 1 2 dimensions. We quantitatively evaluate the relevance of the Hall current in the reconnection process by performing a set of simulations with different values of the Hall parameter. We compute the corresponding reconnection rates as a function of time, and explore the spatial structure of the fields in the surroundings of the diffusion region. We quantify the increase of the reconnection rate as a function of the Hall parameter, and confirm the presence of a quadrupolar structure for the out-of-plane magnetic field.

Simulations of the Small‐Scale Turbulent Dynamo

We report the results of an extensive numerical study of the small-scale turbulent dynamo. The primary focus is on the case of large magnetic Prandtl numbers Prm, which is relevant for hot low-density astrophysical plasmas. A Prm parameter scan is given for the model case of viscosity-dominated (low Reynolds number) turbulence. We concentrate on three topics: magnetic energy spectra and saturation levels, the structure of the magnetic field lines, and intermittency of the field strength distribution. The main results are as follows: (1) the folded structure of the field (direction reversals at the resistive scale, field lines curved at the scale of the flow) persists from the kinematic to the nonlinear regime; (2) the field distribution is self-similar and appears to be lognormal during the kinematic regime and exponential in the saturated state; and (3) the bulk of the magnetic energy is at the resistive scale in the kinematic regime and remains there after saturation, although the magnetic energy spectrum becomes much shallower. We propose an analytical model of saturation based on the idea of partial two-dimensionalization of the velocity gradients with respect to the local direction of the magnetic folds. The model-predicted saturated spectra are in excellent agreement with numerical results. Comparisons with large-Re, moderate-Prm runs are carried out to confirm the relevance of these results and to test heuristic scenarios of dynamo saturation. New features at large Re are elongation of the folds in the nonlinear regime from the viscous scale to the box scale and the presence of an intermediate nonlinear stage of slower than exponential magnetic energy growth accompanied by an increase of the resistive scale and partial suppression of the kinetic energy spectrum in the inertial range. Numerical results for the saturated state do not support scale-by-scale equipartition between magnetic and kinetic energies, with a definite excess of magnetic energy at small scales. A physical picture of the saturated state is proposed. Subject heading gs: magnetic fields — methods: numerical — MHD — plasmas — turbulence

Metastatic breast cancer (19 years later) mimicking obstructing primary colon cancer

A correct description of the ionization balance of high-Z ions, i.e., the fractional abundance of different charge states of a particular element, is critical for interpreting diagnostic line ratios, for describing radiation flow within and out of the plasma, and for assessing the energy balance of high-temperature plasmas. Despite the fundamental nature of this atomic physics parameter, the ionization balance as a function of plasma electron density and electron temperature is generally rather poorly known both experimentally and theoretically. This is the case irregardless of the type of plasma, i.e., low-density astrophysical and coronal plasmas, intermediate density magnetically confined fusion plasmas, or high energy density (HED) laboratory plasmas. We illustrate these points by reviewing existing measurements of the ionization balance of high-Z elements in high-temperature plasmas and discussing the difficulties associated with ionization balance calculations. We focus on the two high-Z elements tungsten (Z = 74) and gold (Z = 79), which play important roles in magnetic fusion and HED plasmas and for which we present calculations of the ionization energies for each charge state. We show that the accuracy of the treatment of dielectronic recombination is currently a limiting factor in proper modeling of the ionization balance and propose “differential” measurements that determine the amount of dielectronic recombination concurrently with the ionization balance as the next step for advancing ionization balance modeling. As an example of the differential measurement approach, we present recent experiments carried out at the Livermore electron beam ion trap, which investigated the ionization balance of gold in the presence of beam-resonant dielectronic recombination. These plasmas limit the immense complexity of dielectronic recombination resonances so that both approximate and reasonably complete detailed calculations can be compared to the measurements. This represents a path forward for constructing and selecting those approximations that produce the most reliable ionization balance models.

X-ray spectropolarimetry of high-temperature plasmas

X-ray spectropolarimetry is a powerful new tool for investigating the anisotropy of high-temperature plasmas. It is sensitive to the energetic electron distribution function and magnetic field, which, in general, have not been measured adequately. This diagnostic is based on the theoretical modeling of x-ray line polarization-dependent spectra measured simultaneously by spectrometers with different sensitivities to polarization. The increasing sophistication of spectroscopic monitoring of high-temperature plasmas has led to the necessity to account for both non-Maxwellian electron distribution functions and polarization properties of lines. This diagnostic can be applied to a broad range of plasmas, from low-density astrophysical plasmas to dense z-pinch plasmas. This work shows how x-ray spectropolarimetry complements the usual spectroscopic monitoring of hot plasmas and demonstrates the importance of accounting for x-ray line polarization in plasma diagnostics.

Influence of atomic radiative and collisional processes on the plasma modeling of Mg^{10+} at low electron densities

In this paper, we report on theoretical calculations of electron-impact excitation cross sections and radiative transition rates for ${\mathrm{Mg}}^{10+}.$ The excitation cross sections were calculated using semirelativistic close-coupling and fully relativistic distorted-wave theory and the radiative rates were determined using semirelativistic and fully relativistic atomic-structure theory. After the solution of the corresponding collisional-radiative equations, the $K{\ensuremath{\alpha}}_{2}/K{\ensuremath{\alpha}}_{1}$ $(1s2p{ }^{3}{P}_{1}\ensuremath{\rightarrow}{1s}^{2}{ }^{1}{S}_{0}$ over $1s2p{ }^{1}{P}_{1}\ensuremath{\rightarrow}{1s}^{2}{ }^{1}{S}_{0})$ emission line ratio and the $K{\ensuremath{\beta}}_{2}/K{\ensuremath{\beta}}_{1}$ $(1s3p{ }^{3}{P}_{1}\ensuremath{\rightarrow}{1s}^{2}{ }^{1}{S}_{0}$ over $1s3p{ }^{1}{P}_{1}\ensuremath{\rightarrow}{1s}^{2}{ }^{1}{S}_{0})$ emission line ratio were calculated as a function of electron temperature and density. The various scattering calculations involving different numbers of levels enabled us to study the influence of resonance structures and cascades from highly excited levels on the collisional-radiative modeling and we found that they have little effect on the level populations. However, even in this ten-times ionized species, the effects of orbital relaxation are found to be important in the determination of accurate electric-dipole radiative transition rates. Both line ratios were found to be strongly affected by whether the magnetic-dipole radiative transition from the $1s2s$ ${}^{3}{S}_{1}$ level to the ground state was included or not. At very low electron densities, the $1s2s$ ${}^{1}{S}_{0}$ two-photon transition to the ground state also has an effect on the $K{\ensuremath{\alpha}}_{2}/K{\ensuremath{\alpha}}_{1}$ line ratio. In addition, we found that the line ratios are enhanced at high temperatures by radiative and dielectronic recombination from the hydrogenic ${\mathrm{Mg}}^{11+}$ ion. However, the dielectronic satellite lines have no effect on the line ratios for the low-density astrophysical, solar, and magnetic-fusion plasmas considered in this paper.

Cooling functions for low-density astrophysical plasmas

view Abstract Citations (2094) References (80) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Cooling Functions for Low-Density Astrophysical Plasmas Sutherland, Ralph S. ; Dopita, M. A. Abstract The cooling functions for a plasma slab are investigated under equilibrium and nonequilibrium conditions, over a range of 10 exp 4 - 10 exp 8.5 K and for a range of abundances. Radiative transfer and diffuse field are calculated in the isobaric nonequilibrium models using a one-dimensional cooling flow model, and the plasma is not assumed to be optically thin to all radiation. Limiting cases of the plasma diffuse field coupling are calculated, and the resulting cooling functions are presented. Some functions are terminated before reaching 10 exp 4 K when the internal photoionization halts the cooling. The functions represent a self-consistent set of curves covering a wide grid of temperature and metallicities using recently published atomic data and processes. The results have implications for phenomena such as cooling flows and for hydrodynamic modeling which include gas components. Publication: The Astrophysical Journal Supplement Series Pub Date: September 1993 DOI: 10.1086/191823 Bibcode: 1993ApJS...88..253S Keywords: Cooling Flows (Astrophysics); Cosmic Plasma; Nonequilibrium Ionization; One Dimensional Flow; Plasma Slabs; Radiative Transfer; Charge Exchange; Electron Impact; Grid Generation (Mathematics); Hydrogen Recombinations; Ionization; Mathematical Models; Metallicity; Photoionization; Radiative Recombination; Rarefied Plasmas; Resonance Lines; Astrophysics; ATOMIC PROCESSES; GALAXIES: COOLING FLOWS; PLASMAS; RADIATIVE TRANSFER full text sources ADS |