1,000 research outputs found
Revisited abundance diagnostics in quasars: Fe II/Mg II ratios
Both the Fe II UV emission in the 2000- 3000 A region [Fe II (UV)] and
resonance emission line complex of Mg II at 2800 A are prominent features in
quasar spectra. The observed Fe II UV/ Mg II emission ratios have been proposed
as means to measure the buildup of the Fe abundance relative to that of the
alpha-elements C, N, O, Ne and Mg as a function of redshift. The current
observed ratios show large scatter and no obvious dependence on redshift. Thus,
it remains unresolved whether a dependence on redshift exists and whether the
observed Fe II UV/ Mg II ratios represent a real nucleosynthesis diagnostic. We
have used our new 830-level model atom for Fe+ in photoionization calculations,
reproducing the physical conditions in the broad line regions of quasars. This
modeling reveals that interpretations of high values of Fe II UV/ Mg II are
sensitive not only to Fe and Mg abundance, but also to other factors such as
microturbulence, density, and properties of the radiation field. We find that
the Fe II UV/ Mg II ratio combined with Fe II (UV)/ Fe II (Optical) emission
ratio, where Fe II (Optical) denotes Fe II emission in 4000 - 6000 A can be
used as a reliable nucleosynthesis diagnostic for the Fe/Mg abundance ratios
for the physical conditions relevant to the broad-line regions (BLRs) of
quasars. This has extreme importance for quasar observations with the Hubble
Space Telescope and also with the future James Webb Space Telescope.Comment: kverner.gzip, 9 pages, f1-5.eps; aastex.cls; aastexug.sty, ApJL in
pres
THE USE OF DISCRETE VARIABLES TO ESTIMATE PRICE AND INCOME ELASTICITIES FOR PRODUCTS WITH SEASONAL CONSUMPTION PATTERNS
Food Consumption/Nutrition/Food Safety,
Fe II Diagnostic Tools for Quasars
The enrichment of Fe, relative to alpha-elements such as O and Mg, represents
a potential means to determine the age of quasars and probe the galaxy
formation epoch.
To explore how \ion{Fe}{2} emission in quasars is linked to physical
conditions and abundance, we have constructed a 830-level \ion{Fe}{2} model
atom and investigated through photoionization calculations how \ion{Fe}{2}
emission strengths depend on non-abundance factors. We have split \ion{Fe}{2}
emission into three major wavelength bands, \ion{Fe}{2} (UV),
\ion{Fe}{2}(Opt1), and \ion{Fe}{2}(Opt2), and explore how the
\ion{Fe}{2}(UV)/\ion{Mg}{2}, \ion{Fe}{2}(UV)/\ion{Fe}{2}(Opt1) and
\ion{Fe}{2}(UV)/\ion{Fe}{2}(Opt2) emission ratios depend upon hydrogen density
and ionizing flux in broad-line regions (BLR's) of quasars. Our calculations
show that: 1) similar \ion{Fe}{2}(UV)/\ion{Mg}{2} ratios can exist over a wide
range of physical conditions; 2) the \ion{Fe}{2}(UV)/\ion{Fe}{2}(Opt1) and
\ion{Fe}{2}(UV)/\ion{Fe}{2}(Opt2) ratios serve to constrain ionizing luminosity
and hydrogen density; and 3) flux measurements of \ion{Fe}{2} bands and
knowledge of ionizing flux provide tools to derive distances to BLR's in
quasars. To derive all BLR physical parameters with uncertainties, comparisons
of our model with observations of a large quasar sample at low redshift ()
is desirable.
The STIS and NICMOS spectrographs aboard the Hubble Space Telescope (HST)
offer the best means to provide such observations.Comment: ApJ accepte
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
An Atlas of Computed Equivalent Widths of Quasar Broad Emission Lines
We present graphically the results of several thousand photoionization
calculations of broad emission line clouds in quasars, spanning seven orders of
magnitude in hydrogen ionizing flux and particle density. The equivalent widths
of 42 quasar emission lines are presented as contours in the particle density -
ionizing flux plane for a typical incident continuum shape, solar chemical
abundances, and cloud column density of . Results are
similarly given for a small subset of emission lines for two other column
densities ( and ), five other incident
continuum shapes, and a gas metallicity of 5 \Zsun. These graphs should prove
useful in the analysis of quasar emission line data and in the detailed
modeling of quasar broad emission line regions. The digital results of these
emission line grids and many more are available over the Internet.Comment: 16 pages, LaTeX (AASTeX aaspp4.sty); to appear in the 1997 ApJS: full
contents of the 9 photoionization grids presented in this paper may be found
at http://www.pa.uky.edu/~korista/grids/grids.htm
Identification of Emission Lines in the Low-Ionization Strontium Filament Near Eta Carinae
We have obtained deep spectra from 1640 to 10100A with the Space Telescope
Imaging Spectrograph (STIS) of the Strontium Filament, a largely neutral
emission nebulosity lying close to the very luminous star Eta Carinae and
showing an uncommon spectrum. Over 600 emission lines, both permitted and
forbidden, have been identified. The majority originates from neutral or
singly-ionized iron group elements (Sc, Ti, V, Cr, Mn, Fe, Co, Ni). Sr is the
only neutron capture element detected. The presence of Sr II, numerous strong
Ti II and V II lines and the dominance of Fe I over Fe II are notable
discoveries. While emission lines of hydrogen, helium, and nitrogen are
associable with other spatial structures at other velocities within the
Homunculus, no emission lines from these elements correspond to the spatial
structure or velocity of the Sr Filament. Moreover, no identified Sr Filament
emission line requires an ionization or excitation energy above approximately 8
eV. Ionized gas extends spatially along the aperture, oriented along the polar
axis of the Homunculus, and in velocity around the Strontium Filament. We
suggest that the Strontium Filament is shielded from ultraviolet radiation at
energies above 8 eV, but is intensely irradiated by the central star at
wavelengths longward of 1500A.Comment: 28 pages, 5 figures, 4 tables. Accepted by A&A. High resolution
pictures can be found at http://www.astro.lu.se/~henrikh/srpaper/srpaper.pd
Deposing the Cool Corona of KPD 0005+5106
The ROSAT PSPC pulse height spectrum of the peculiar He-rich hot white dwarf
KPD 0005+5106 provided a great surprise when first analysed by Fleming, Werner
& Barstow (1993). It defied the best non-LTE modelling attempts in terms of
photospheric emission from He-dominated atmospheres including C, N and O and
was instead interpreted as the first evidence for a coronal plasma around a
white dwarf. We show here that a recent high resolution Chandra LETGS spectrum
has more structure than expected from a thermal bremsstrahlung continuum and
lacks the narrow lines of H-like and He-like C expected from a coronal plasma.
Moreover, a coronal model requires a total luminosity more than two orders of
magnitude larger than that of the star itself. Instead, the observed 20-80 AA
flux is consistent with photospheric models containing trace amounts of heavier
elements such as Fe. The soft X-ray flux is highly sensitive to the adopted
metal abundance and provides a metal abundance diagnostic. The weak X-ray
emission at 1 keV announced by O'Dwyer et al (2003) instead cannot arise from
the photosphere and requires alternative explanations. We echo earlier
speculation that such emission arises in a shocked wind. Despite the presence
of UV-optical O VIII lines from transitions between levels n=7-10, no X-ray O
VIII Ly alpha flux is detected. We show that O VIII Lyman photons can be
trapped by resonant scattering within the emitting plasma and destroyed by
photoelectric absorption.Comment: 15 Pages, 4 figures. Accepted for the Astrophysical Journa
Numerical Simulations of Fe II Emission Spectra
This paper describes the techniques that we have used to incorporate a large-scale model of the Fe+ ion and resulting Fe IIemission into CLOUDY, a spectral synthesis code designed to simulate conditions within a plasma and model the resulting spectrum. We describe the numerical methods we use to determine the level populations, mutual line overlap fluorescence, collisional effects, and the heating-cooling effects of the atom on its environment. As currently implemented, the atom includes the lowest 371 levels (up to 11.6 eV) and predicts intensities of 68,635 lines. We describe our data sources, which include the most recent transition probabilities and collision strengths. Although we use detailed fits to temperature-dependent collision strengths where possible, in many cases the uncertain g approximation is the only source for collision data. The atom is designed to be readily expanded to include more levels and to incorporate more accurate sets of collision and radiative data as computers grow faster and the atomic databases expand. We present several test cases showing that the atom goes to LTE in the limits of high particle and radiation densities. We give an overview of general features of the Fe II spectra as their dependencies on the basic parameters of our models (density, flux, microturbulent velocity, the Fe abundance, and Lyα pumping). Finally, we discuss several applications to active galactic nuclei to illustrate the diagnostic power of the Fe II spectrum and make some predictions for UV observations
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