510 research outputs found
[O II] line ratios
Based on new calculations we reconfirm the low and high density limits on the
forbidden fine structure line ratio [O II] I(3729)/I(3726): lim_{N_ e} --> 0} =
1.5 and lim_{N_ e} --> \infty} = 0.35. Employing [O II] collision strengths
calculated using the Breit-Pauli R-matrix method we rule out any significant
deviation due to relativistic effects from these canonical values. The present
results are in substantial agreement with older calculations by Pradhan (1976)
and validate the extensive observational analysis of gaseous nebulae by Copetti
and Writzel (2002) and Wang et al (2004) that reach the same conclusions. The
present theoretical results and the recent observational analyses differ
significantly from the calculations by MacLaughlin and Bell (1998) and Keenan
et al (1999). The new maxwellian averaged effective collision strengths are
presented for the 10 transitions among the first 5 levels to enable
computations of [O II] line ratios.Comment: Submitted to MNRAS (Letters), 4 pages, 2 figures, 1 tabl
Improved collision strengths and line ratios for forbidden [O III] far-infrared and optical lines
Far-infrared and optical [O III] lines are useful temeprature-density
diagnostics of nebular as well as dust obscured astrophysical sources. Fine
structure transitions among the ground state levels 1s^22s^22p^3 \ ^3P_{0,1,2}
give rise to the 52 and 88 micron lines, whereas transitions among the
levels yield the well-known optical lines 4363,
4959 and 5007 Angstroms. These lines are excited primarily by electron impact
excitation. But despite their importance in nebular diagnostics collision
strengths for the associated fine structure transitions have not been computed
taking full account of relativistic effects. We present Breit-Pauli R-matrix
calculations for the collision strengths with highly resolved resonance
structures. We find significant differences of up to 20% in the Maxwellian
averaged rate coefficients from previous works. We also tabulate these to lower
temperatures down to 100 K to enable determination of physical conditions in
cold dusty environments such photo-dissociation regions and ultra-luminous
infrared galaxies observed with the Herschel space observatory. We also examine
the effect of improved collision strengths on temperature and density sensitive
line ratios.Comment: Letter in press, Monthly Notices of Royal Astronomical Society, 5
pages, 6 figure
Atomic data from the Iron Project. LIII. Relativistic allowed and forbidden transition probabilities for Fe XVII
An extensive set of fine structure levels and corresponding transition
probabilities for allowed and forbidden transitions in Fe XVII is presented. A
total of 490 bound energy levels of Fe XVII of total angular momenta 0 <= J <=
7 of even and odd parities with 2 <= n <= 10, 0 <= l <= 8, 0 <= L <= 8, and
singlet and triplet multiplicities, are obtained. They translate to over 2.6 x
10^4 allowed (E1) transitions that are of dipole and intercombination type, and
about 3000 forbidden transitions that include electric quadrupole (E2),
magnetic dipole (M1), electric octopole (E3), and magnetic quadrupole (M2) type
representing the most detailed calculations to date for the ion. Oscillator
strengths f, line strengths S, and coefficients A of spontaneous emission for
the E1 type transitions are obtained in the relativistic Breit-Pauli R-matrix
approximation. A valus for the forbidden transitions are obtained from atomic
structure calculations using codes SUPERSTRUCTURE and GRASP. The energy levels
are identified in spectroscopic notation with the help of a newly developed
level identification algorithm. Nearly all 52 spectroscopically observed levels
have been identified, their binding energies agreeing within 1% with our
calculation. Computed transition probabilities are compared with other
calculations and measurement. The effect of 2-body magnetic terms and other
interactions is discussed. Present data set enhances by more than an order of
magnitude the heretofore available data for the transition probabilities of Fe
XVII.Comment: Submitted to Astron. Astrophys., 13 pages : Radiative data for
Ne-like Iron for X-ray and EUV application
R-Matrix calculations for opacities: I. Methodology and computations
An extended version of the R-matrix methodology is presented for calculation
of radiative parameters for improved plasma opacities. Contrast and comparisons
with existing methods primarily relying on the Distorted Wave (DW)
approximation are discussed to verify accuracy and resolve outstanding issues,
particularly with reference to the Opacity Project (OP). Among the improvements
incorporated are: (i) large-scale Breit-Pauli R-matrix (BPRM) calculations for
complex atomic systems including fine structure, (ii) convergent close coupling
wave function expansions for the (e+ion) system to compute oscillator strengths
and photoionization cross sections, (iii) open and closed shell iron ions of
interest in astrophysics and experiments, (iv) a treatment for plasma
broadening of autoionizing resonances as function of energy-temperature-density
dependent cross sections, (v) a "top-up" procedure to compare convergence with
R-matrix calculations for highly excited levels, and (vi) spectroscopic
identification of resonances and bound \eion levels. The present R-matrix
monochromatic opacity spectra are fundamentally different from OP and lead to
enhanced Rosseland and Planck mean opacities. An outline of the work reported
in other papers in this series and those in progress is presented. Based on the
present re-examination of the OP work, it is evident that opacities of heavy
elements require revisions in high temperature-density plasma sources.Comment: 16 pages, 2 figure
A comprehensive set of UV and x-ray radiative transition rates for Fe XVI
Sodium-like Fe XVI is observed in collisionally ionized plasmas such as stellar coronae and coronal line regions of active galactic nuclei including black hole-accretion disc environments. Given its recombination edge from neon-like Fe XVII at ~25 Å, the Fe XVI bound-bound transitions lie in the soft x-ray and EUV (extreme ultraviolet) range. We present a comprehensive set of theoretical transition rates for radiative dipole allowed E1 transitions including fine structure for levels with nℓ(SLJ) ≤ 10, ℓ ≤ 9 using the relativistic Breit-Pauli R-matrix (BPRM) method. In addition, forbidden transitions of electric quadrupole (E2), electric octupole (E3), magnetic dipole (M1) and magnetic quadrupole (M2) type are presented for levels up to 5g(SLJ) from relativistic atomic structure calculations in the Breit-Pauli approximation using code SUPERSTRUCTURE. Some of the computed levels are autoionizing, and oscillator strengths among those are also provided. BPRM results have been benchmarked with the relativistic coupled cluster method and the atomic structure Dirac-Fock code GRASP. Levels computed with the electron collision BPRM codes in bound state mode were identified with a procedure based on the analysis of quantum defects and asymptotic wavefunctions. The total number of Fe XVI levels considered is 96, with 822 E1 transitions. Tabulated values are presented for the oscillator strengths f, line strengths S and Einstein radiative decay rates A. This extensive dataset should enable spectral modelings up to highly excited levels, including recombination-cascade matrices.This work was partially supported by the NASA Astronomy and Physics Research Program and the Astrophysical Theory Program. The computational work was carried out at the Ohio Supercomputer Center in Columbus, Ohio. CS acknowledges discussions with Professor B P Das, Professor D Mukherjee and Professor R K Chaudhuri
Absorption spectra of Fe L-lines in Seyfert 1 galaxies
Absorption L-lines of iron ions are observed, in absorption, in spectra of
Seyfert 1 galaxies by the new generation of X-ray satellites: Chandra (NASA)
and XMM-Newton (ESA). Lines associated to Fe23+ to Fe17+ are well resolved.
Whereas, those corresponding to Fe16+ to Fe6+ are unresolved. Forbidden
transitions of the Fe16+ to Fe6+ ions were previously observed, for the same
objects, in the visible and infra-red regions, showing that the plasma had a
low density. To interpret X-ray, visible and infra-red data, astrophysical
models assume an extended absorbing medium of very low density surrounding an
intense X-ray source. We have calculated atomic data (wavelengths, radiative
and autoionization rates) for n=2 to n'=3-4 transitions and used them to
construct refined synthetic spectra of the unresolved part of the L-line
spectra.Comment: 17 pages, 5 figures, Journal of Quantitative Spectroscopy and
Radiative Transfer, in pres
Kommunikative Erreichbarkeit - Lust oder Frust?
Die Arbeit handelt davon, wie im Raum Wien lebende, erwachsene Personen die neuen Medien interpersonaler Kommunikation wahrnehmen, in Bezug auf die Erreichbarkeit beurteilen und mit ihnen umgehen. Die Fragestellungen wurden anhand einer Tagebuch-Studie und einer Gruppendiskussion, die im Anschluss im Rahmen einer qualitativen Inhaltsanalyse ausgewertet wurden, untersucht. Als Ergebnis kann zusammengefasst werden, dass die Teilnehmer diverse Medien interpersonaler Kommunikation nutzen, sowohl positiv als auch negativ beurteilen und anhand verschiedener Strategien ihre Erreichbarkeit steuern. Der Druckversion wird ein CD-Anhang beigefügt, der neben den Tagebuch-Eintragungen, demographischen Daten, Frage- und Feedback-Bögen auch eine Audio-Datei (Gruppendiskussion) enthält.This paper focuses on how people living in Vienna think about new communications media and how the are used. The main interest ist to find out about their opinions, attitudes, strategies, rules of courtesy and how they feel about availability and time. Therefore two methods are used: diaries and focus groups that are afterwards analysed by a qualitative content analysis. To summarize the results, it can be said that people use different kinds of media, they judge them as well positively as negatively and apply strategies not to be available anytime and anywhere
Advancing Racial Equity Through Community Land Trusts
Community land trusts are nonprofit organizations designed to preserve housing affordability. This brief describes the design and operation of such trusts, illustrating the concept by spotlighting the Columbia Community Land Trust of Columbia, Missouri.
The contents of this brief evolved from a presentation given in the Colloquium on Inclusive Housing Policy for the St. Louis Region. Held in the Brown School at Washington University on December 15, 2022, the event was organized by the Center for Social Development in partnership with Women’s Voices Raised for Social Justice and the Alliance for Interracial Dignity. The contents may also be found in Welcome Home: A Policy Briefing Book for Housing Opportunity in St. Louis County, edited by Molly Metzger
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