186 research outputs found
Large-scale Breit-Pauli R-matrix calculations for transition probabilities of Fe V
Ab initio theoretical calculations are reported for the electric (E1) dipole
allowed and intercombination fine structure transitions in Fe V using the
Breit-Pauli R-matrix (BPRM) method. We obtain 3865 bound fine structure levels
of Fe V and oscillator strengths, Einstein A-coefficients and
line strengths. In addition to the relativistic effects, the intermediate
coupling calculations include extensive electron correlation effects that
represent the complex configuration interaction (CI). Fe V bound levels are
obtained with angular and spin symmetries and of the (e + Fe VI)
system such that = 5,3,1, 10, . The bound levels are
obtained as solutions of the Breit-Pauli (e + ion) Hamiltonian for each ,
and are designated according to the `collision' channel quantum numbers. A
major task has been the identification of these large number of bound fine
structure levels in terms of standard spectroscopic designations. A new scheme,
based on the analysis of quantum defects and channel wavefunctions, has been
developed. The identification scheme aims particularly to determine the
completeness of the results in terms of all possible bound levels for
applications to analysis of experimental measurements and plasma modeling. An
uncertainty of 10-20% for most transitions is estimated.Comment: 31 pages, 1 figure, Physica Scripta (in press
Highly Excited Core Resonances in Photoionization of Fe XVII : Implications for Plasma Opacities
A comprehensive study of high-accuracy photoionization cross sections is
carried out using the relativistic Breit-Pauli R-matrix (BPRM) method for (hnu
+ Fe XVII --> Fe XVIII + e). Owing to its importance in high-temperature
plasmas the calculations cover a large energy range, particularly the myriad
photoexciation-of-core (PEC) resonances including the n = 3 levels not
heretofore considered. The calculations employ a close coupling wave function
expansion of 60 levels of the core ion Fe XVIII ranging over a wide energy
range of nearly 900 eV between the n = 2 and n = 3 levels. Strong coupling
effects due to dipole transition arrays 2p^5 --> 2p^4 (3s,3d) manifest
themselves as large PEC resonances throughout this range, and enhance the
effective photoionization cross sections orders of magnitude above the
background. Comparisons with the erstwhile Opacity Project (OP) and other
previous calculations shows that the currently available cross sections
considerably underestimate the bound-free cross sections. A
level-identification scheme is used for spectroscopic designation of the 454
bound fine structure levels of Fe XVII. Level-specific photoionization cross
sections are computed for all levels. In addition, partial cross sections for
leaving the core ion Fe XVII in the ground state are also obtained. These
results should be relevant to modeling of astrophysical and laboratory plasma
sources requiring (i) photoionization rates, (ii) extensive
non-local-thermodynamic-equilibrium models, (iii) total unified electron-ion
recombination rates including radiative and dielectronic recombination, and
(iv) plasma opacities. We particularly examine PEC and non-PEC resonance
strengths and emphasize their expanded role to incorporate inner-shell
excitations for improved opacities, as shown by the computed monochromatic
opacity of Fe XVII.Comment: 12 pages, 5 figures, Physical Review A (in press
The Importance of Nebular Continuum and Line Emission in Observations of Young Massive Star Clusters
In this spectroscopic study of infant massive star clusters, we find that
continuum emission from ionized gas rivals the stellar luminosity at optical
wavelengths. In addition, we find that nebular line emission is significant in
many commonly used broad-band HST filters including the F814W I-band, the F555W
V-band and the F435W B-band. Two young massive clusters (YMCs) in NGC 4449 were
targeted for spectroscopic observations after Reines et al. (2008a) discovered
an F814W I-band excess in their photometric study of radio-detected clusters in
the galaxy. The spectra were obtained with the Dual Imaging Spectrograph on the
3.5 m APO telescope. We supplement these data with HST and SDSS photometry. By
comparing our data to the Starburst99 and GALEV models, we find that nebular
continuum emission competes with the stellar light in our observations and that
the relative contribution is largest in the U- and I-bands, where the Balmer
and Paschen jumps are located. The spectra also exhibit strong line emission
including the [SIII] 9069,9532 lines in the HST F814W I-band. We find that the
combination of nebular continuum and line emission can account for the F814W
I-band excess found by Reines et al. (2008a). In an effort to provide a
benchmark for estimating the impact of ionized gas emission on photometric
observations of YMCs, we compute the relative contributions of the stellar
continuum, nebular continuum, and emission lines to the total flux of a 3
Myr-old cluster through various HST filter/instrument combinations, including
filters in the WFC3. We urge caution when comparing observations of YMCs to
evolutionary synthesis models since nebular emission can have a large impact on
magnitudes and colors of young (< 5 Myr) clusters, significantly affecting
inferred properties such as ages, masses and extinctions. (Abridged)Comment: 13 pages, 11 figures, Accepted for Publication in Ap
Nitrogen line spectroscopy of O-stars -- I. Nitrogen III emission line formation revisited
This is the first paper in a series dealing with optical Nitrogen
spectroscopy of O-type stars, aiming at the analysis of Nitrogen abundances.
We implemented a new Nitrogen model atom into the NLTE atmosphere/spectrum
synthesis code FASTWIND, and compare the resulting optical NIII lines at
4634/40/42 A with other predictions, mostly from Mihalas & Hummer (1973, ApJ
179, 827,`MH'), and from the alternative code CMFGEN.
Using similar model atmospheres as MH (not blanketed and wind-free), we are
able to reproduce their results, in particular the triplet emission lines.
According to MH, these should be strongly related to dielectronic recombination
(DR) and the drain by certain two-electron transitions. However, using
realistic, fully line-blanketed atmospheres at solar abundances, the key role
of DR controlling these emission features is superseded -- for O-star
conditions -- by the strength of the stellar wind and metallicity. In the case
of wind-free models, the resulting lower ionizing EUV-fluxes severely suppress
the emission. As the mass-loss rate is increased, pumping through the NIII
resonance line(s) in the presence of a near-photospheric velocity field results
in a net optical triplet line emission. A comparison with results from CMFGEN
is mostly satisfactory, except for the range 30 kK < Teff < 35 kK, where CMFGEN
triggers the triplet emission at lower Teff than FASTWIND. This effect could be
traced down to line overlap effects between the NIII and OIII resonance lines
that so far cannot be simulated by FASTWIND.
Since the efficiency of DR and `two electron drain' strongly depends on the
degree of line-blanketing/-blocking, we predict the emission to become stronger
in a metal-poor environment, though lower wind-strengths and Nitrogen
abundances might counteract this effect. Weak winded stars should display less
triplet emission than stars with `normal' winds.Comment: Accepted by Astronomy & Astrophysics. Main paper: 18 pages, 16
figures; Online-appendix: 6 pages, 14 figure
General consensus on multimodal functions and validation analysis of perinatal derivatives for regenerative medicine applications.
Perinatal tissues, such as placenta and umbilical cord contain a variety of somatic stem cell types, spanning from the largely used hematopoietic stem and progenitor cells to the most recently described broadly multipotent epithelial and stromal cells. As perinatal derivatives (PnD), several of these cell types and related products provide an interesting regenerative potential for a variety of diseases. Within COST SPRINT Action, we continue our review series, revising and summarizing the modalities of action and proposed medical approaches using PnD products: cells, secretome, extracellular vesicles, and decellularized tissues. Focusing on the brain, bone, skeletal muscle, heart, intestinal, liver, and lung pathologies, we discuss the importance of potency testing in validating PnD therapeutics, and critically evaluate the concept of PnD application in the field of tissue regeneration. Hereby we aim to shed light on the actual therapeutic properties of PnD, with an open eye for future clinical application. This review is part of a quadrinomial series on functional/potency assays for validation of PnD, spanning biological functions, such as immunomodulation, anti-microbial/anti-cancer, anti-inflammation, wound healing, angiogenesis, and regeneration
Irreducible tensor-form of the relativistic corrections to the M1 transition operator
The relativistic corrections to the magnetic dipole moment operator in the
Pauli approximation were derived originally by Drake (Phys. Rev. A 3(1971)908).
In the present paper, we derive their irreducible tensor-operator form to be
used in atomic structure codes adopting the Fano-Racah-Wigner algebra for
calculating its matrix elements.Comment: 26 page
CHIANTI - an Atomic Database for Emission Lines. Paper VI: Proton Rates and Other Improvements
The CHIANTI atomic database contains atomic energy levels, wavelengths,
radiative transition probabilities and electron excitation data for a large
number of ions of astrophysical interest. Version 4 has been released, and
proton excitation data is now included, principally for ground configuration
levels that are close in energy. The fitting procedure for excitation data,
both electrons and protons, has been extended to allow 9 point spline fits in
addition to the previous 5 point spline fits. This allows higher quality fits
to data from close-coupling calculations where resonances can lead to
significant structure in the Maxwellian-averaged collision strengths. The
effects of photoexcitation and stimulated emission by a blackbody radiation
field in a spherical geometry on the level balance equations of the CHIANTI
ions can now be studied following modifications to the CHIANTI software. With
the addition of H I, He I and N I, the first neutral species have been added to
CHIANTI. Many updates to existing ion data-sets are described, while several
new ions have been added to the database, including Ar IV, Fe VI and Ni XXI.
The two-photon continuum is now included in the spectral synthesis routines,
and a new code for calculating the relativistic free-free continuum has been
added. The treatment of the free-bound continuum has also been updated.Comment: CHIANTI is available at http://wwwsolar.nrl.navy.mil/chianti.htm
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