813 research outputs found
Atomic Data for Permitted Resonance Lines of Atoms and Ions from H to Si, and S, Ar, Ca and Fe
We list vacuum wavelengths, energy levels, statistical weights, transition
probabilities and oscillator strengths for permitted resonance spectral lines
of all ions of 18 astrophysically important elements (H through Si, S, Ar, Ca,
Fe). Using a compilation of experimental energy levels, we derived accurate
wavelengths for 5599 lines of 1828 ground-term multiplets which have gf-values
calculated in the Opacity Project. We recalculated the Opacity Project
multiplet gf-values to oscillator strengths and transition probabilities of
individual lines. For completeness, we added 372 resonance lines of NeI, ArI,
FeI and FeII ions which are not covered by the Opacity Project.
Intercombination and forbidden lines are not included in the present
compilation.Comment: 6 pages of text, latex, 1 figure, 4 tables; tables in ASCII format
available at ftp://asta.pa.uky.edu/dima/lines/ or at
http://www.pa.uky.edu/~verner/atom.html Accepted by Atomic Data Nucl. Data
Table
Atomic Data for Astrophysics. II. New Analytic Fits for Photoionization Cross Sections of Atoms and Ions
We present a complete set of analytic fits to the non-relativistic
photoionization cross sections for the ground states of atoms and ions of
elements from H through Si, and S, Ar, Ca, and Fe. Near the ionization
thresholds, the fits are based on the Opacity Project theoretical cross
sections interpolated and smoothed over resonances. At higher energies, the
fits reproduce calculated Hartree-Dirac-Slater photoionization cross sections.Comment: 24 pages including Postscript figures and tables, uses aaspp4.sty,
accepted for publication in Astrophysical Journal. Misprint in Eq.(1) is
correcte
Continuum Pumping of [Fe II] in the Orion Nebula
This paper presents detailed comparisons between numerical simulations of Fe II emission spectra and recent high-resolution and signal-to-noise spectra of the Orion Nebula. We have identified 40 [Fe II] lines in the spectrum, allowing extensive comparisons between theory and observations. The identifications are based on predictions of a realistic model of the Fe II atom, which includes the lowest 371 levels (all levels up to 11.6 eV). We investigate the dependence of the spectrum on electron density and on pumping by the stellar continuum. Orion is important because it provides a relatively simple environment in which to test complex simulations. We have identified the pumping routes that are responsible for the observed emission. Our theoretical model of Fe II emission is in good agreement with the observational data
The Molecular Structure of Cyclopropene, C_3C_4
Cyclopropene, C_3H_4, has been investigated by the electron diffraction method. The cyclic structure is confirmed and the following interatomic distances and angles are found: CâC, 1.525±0.02 A; C=C, 1.286±0.04 A; ăCâHă, 1.087±0.04 A; â HâCâH, 118° (assumed); â C=CâH, 152±12°
Scattering by Interstellar Dust Grains. II. X-Rays
Scattering and absorption of X-rays by interstellar dust is calculated for a
model consisting of carbonaceous grains and amorphous silicate grains. The
calculations employ realistic dielectric functions with structure near X-ray
absorption edges, with resulting features in absorption, scattering, and
extinction.
Differential scattering cross sections are calculated for energies between
0.3 and 10 keV. The median scattering angle is given as a function of energy,
and simple but accurate approximations are found for the X-ray scattering
properties of the dust mixture, as well as for the angular distribution of the
scattered X-ray halo for dust with simple spatial distributions. Observational
estimates of the X-ray scattering optical depth are compared to model
predictions. Observations of X-ray halos to test interstellar dust grain models
are best carried out using extragalactic point sources.Comment: ApJ, accepted. 27 pages, 12 figures. Much of this material was
previously presented in astro-ph/0304060v1,v2,v3 but has been separated into
the present article following recommendation by the refere
XMM-Newton and INTEGRAL observations of the black hole candidate XTE J1817-330
The galactic black hole candidate XTE J1817-330 was discovered in outburst by
RXTE in January 2006. We present here the results of an XMM-Newton Target of
opportunity observation (TOO), performed on 13 March 2006 (44 days after the
maximum), and an INTEGRAL observation performed on 15-18 February 2006 (18 days
after the maximum). The EPIC-pn camera on-board XMM-Newton was used in the fast
read-out Burst mode to avoid photon pile-up, while the RGSs were used in
Spectroscopy high count-rate mode. We fit both the XMM-Newton and the INTEGRAL
spectra with a two-component model consisting of a thermal accretion disk and a
comptonizing hot corona. The soft X-ray spectrum is dominated by an accretion
disk component, with a maximum temperature decreasing from 0.96+/-0.04 keV at
the time of the INTEGRAL observation to 0.70+/-m0.01 keV on 13 March. The
Optical Monitors on board INTEGRAL and XMM-Newton showed the source with
magnitudes V: 11.3-11.4, U:15.0-15.1 and UVW1:14.7-14.8. The soft X-ray
spectrum, together with the optical and UV data, show a low hydrogen column
density towards the source, and several absorption lines, most likely of
interstellar origin, are detected in the RGS spectrum: OI K-alpha, OI K-beta,
OII, OIII and OVII, which trace both cold and hot components of the ISM. The
soft X-ray spectrum indicates the presence of a black hole, with an estimate
for the upper limit of the mass of 6.0(+4.0/-2.5) Msun.Comment: Accepted for publication in A&
Luminosity indicators in dusty photoionized environments
The luminosity of the central source in ionizing radiation is an essential
parameter in a photoionized environment, and one of the most fundamental
physical quantities one can measure. We outline a method of determining
luminosity for any emission-line region using only infrared data. In dusty
environments, grains compete with hydrogen in absorbing continuum radiation.
Grains produce infrared emission, and hydrogen produces recombination lines. We
have computed a very large variety of photoionization models, using ranges of
abundances, grain mixtures, ionizing continua, densities, and ionization
parameters. The conditions were appropriate for such diverse objects as H II
regions, planetary nebulae, starburst galaxies, and the narrow and broad line
regions of active nuclei. The ratio of the total thermal grain emission
relative to H (IR/H) is the primary indicator of whether the
cloud behaves as a classical Str\"{o}mgren sphere (a hydrogen-bounded nebula)
or whether grains absorb most of the incident continuum (a dust-bounded
nebula). We find two global limits: when infrared recombination
lines determine the source luminosity in ionizing photons; when
the grains act as a bolometer to measure the luminosity.Comment: 12 pages 3 figures. Accepted ASP Sept.9
Physical Conditions in Low Ionization Regions of the Orion Nebula
We reexamine the spectroscopic underpinnings of recent suggestions that [O I]
and [Fe II] lines from the Orion H II region are produced in gas where the
iron-carrying grains have been destroyed and the electron density is
surprisingly high. Our new observations show that previous detections of [O I]
5577 were dominated by telluric emission. Our limits are consistent with a
moderate density (10^4 cm^{-3}) photoionized gas. We show that a previously
proposed model of the Orion H II region reproduces the observed [O I] and [Fe
II] spectrum. These lines are fully consistent with formation in a dusty region
of moderate density.Comment: 12 pages, latex (aaspp4.sty), 1 figure. To appear in ApJ Letter
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