364 research outputs found
The broadening of Fe II lines by neutral hydrogen collisions
Data for the broadening of 24188 Fe II lines by collisions with neutral
hydrogen atoms have been computed using the theory of Anstee & O'Mara as
extended to singly ionised species and higher orbital angular momentum states
by Barklem & O'Mara. Data have been computed for all Fe II lines between
observed energy levels in the line lists of Kurucz with log gf > -5 for which
the theory is applicable. The variable energy debt parameter Ep used in
computing the second order perturbation theory potential is chosen to be
consistent with the long range dispersion interaction constant C6 computed
using the f-values from Kurucz.Comment: Accepted for A&A. 5 pages, 5 figures, 2 electronic tables. Tables
will be available via CDS; presently also at
http://www.astro.uu.se/~barklem/papers/fe2_data.tar.g
Excitation and charge transfer in low-energy hydrogen atom collisions with neutral oxygen
Excitation and charge transfer in low-energy O+H collisions is studied; it is
a problem of importance for modelling stellar spectra and obtaining accurate
oxygen abundances in late-type stars including the Sun. The collisions have
been studied theoretically using a previously presented method based on an
asymptotic two-electron linear combination of atomic orbitals (LCAO) model of
ionic-covalent interactions in the neutral atom-hydrogen-atom system, together
with the multichannel Landau-Zener model. The method has been extended to
include configurations involving excited states of hydrogen using an estimate
for the two-electron transition coupling, but this extension was found to not
lead to any remarkably high rates. Rate coefficients are calculated for
temperatures in the range 1000 - 20000 K, and charge transfer and
(de)excitation processes involving the first excited S-states, 4s.5So and
4s.3So, are found to have the highest rates.Comment: Accepted for A&A. Data will be made available at CDS. Is available
here: https://github.com/barklem/public-data. Replaced version corrects url
and adds it to the pape
Excitation and charge transfer in low-energy hydrogen atom collisions with neutral iron
Data for inelastic processes due to hydrogen atom collisions with iron are
needed for accurate modelling of the iron spectrum in late-type stars.
Excitation and charge transfer in low-energy Fe+H collisions is studied
theoretically using a previously presented method based on an asymptotic
two-electron linear combination of atomic orbitals (LCAO) model of
ionic-covalent interactions in the neutral atom-hydrogen-atom system, together
with the multi-channel Landau-Zener model. An extensive calculation including
166 covalent states and 25 ionic states is presented and rate coefficients are
calculated for temperatures in the range 1000 - 20000 K. The largest rates are
found for charge transfer processes to and from two clusters of states around
6.3 and 6.6 eV excitation, corresponding in both cases to active 4d and 5p
electrons undergoing transfer. Excitation and de-excitation processes among
these two sets of states are also significant.Comment: Accepted by A&
Partition functions and equilibrium constants for diatomic molecules and atoms of astrophysical interest
Partition functions and dissociation equilibrium constants are presented for
291 diatomic molecules for temperatures in the range from near absolute zero to
10000 K, thus providing data for many diatomic molecules of astrophysical
interest at low temperature. The calculations are based on molecular
spectroscopic data from the book of Huber and Herzberg with significant
improvements from the literature, especially updated data for ground states of
many of the most important molecules by Irikura. Dissociation energies are
collated from compilations of experimental and theoretical values. Partition
functions for 284 species of atoms for all elements from H to U are also
presented based on data collected at NIST. The calculated data are expected to
be useful for modelling a range of low density astrophysical environments,
especially star-forming regions, protoplanetary disks, the interstellar medium,
and planetary and cool stellar atmospheres. The input data, which will be made
available electronically, also provides a possible foundation for future
improvement by the community.Comment: 13 pages, 8 figures, 8 tables. Full tables 1, 2, 4, 5, 6, 7 and 8 to
be made available in electronic form at the CDS via anonymous ftp to
cdsarc.u-strasbg.fr (130.79.128.5) or via
http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A
A unified numerical model of collisional depolarization and broadening rates due to hydrogen atom collisions
Interpretation of solar polarization spectra accounting for partial or
complete frequency redistribution requires data on various collisional
processes. Data for depolarization and polarization transfer are needed but
often missing, while data for collisional broadening are usually more readily
available. Recent work by Sahal-Br\'echot and Bommier concluded that despite
underlying similarities in the physics of collisional broadening and
depolarization processes, relationships between them are not possible to derive
purely analytically.
We aim to derive accurate numerical relationships between the collisional
broadening rates and the collisional depolarization and polarization transfer
rates due to hydrogen atom collisions. Such relationships would enable accurate
and efficient estimation of collisional data for solar applications.
Using earlier results for broadening and depolarization processes based on
general (i.e. not specific to a given atom), semi-classical calculations
employing interaction potentials from perturbation theory, genetic programming
(GP) has been used to fit the available data and generate analytical functions
describing the relationships between them. The predicted relationships from the
GP-based model are compared with the original data to estimate the accuracy of
the method.Comment: 10 pages, 7 figures, Accepted for publication in Astronomy &
Astrophysic
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