515 research outputs found
Line absorption of He-like triplet lines by Li-like ions. Caveats of using line ratios of triplets for plasma diagnostics
He-like ions produce distinctive series of triplet lines under various
astrophysical conditions. However, this emission can be affected by line
absorption from Li-like ions in the same medium. We investigate this absorption
of He-like triplets and present the implications for diagnostics of plasmas in
photoionisation equilibrium using the line ratios of the triplets. Our
computations were carried out for the O VI and Fe XXIV absorption of the O VII
and Fe XXV triplet emission lines, respectively. The fluorescent emission by
the Li-like ions and continuum absorption of the He-like ion triplet lines are
also investigated. We determine the absorption of the triplet lines as a
function of Li-like ion column density and velocity dispersion of the emitting
and absorbing medium. We find O VI line absorption can significantly alter the
O VII triplet line ratios in optically-thin plasmas, by primarily absorbing the
intercombination lines, and to a lesser extent, the forbidden line. Because of
intrinsic line absorption by O VI inside a photoionised plasma, the predicted
ratio of forbidden to intercombination line intensity for the O VII triplet
increases from 4 up to an upper limit of 16. This process can explain the
triplet line ratios that are higher than expected and that are seen in some
X-ray observations of photoionised plasmas. For the Fe XXV triplet, line
absorption by Fe XXIV becomes less apparent owing to significant fluorescent
emission by Fe XXIV. Without taking the associated Li-like ion line absorption
into account, the density diagnosis of photoionised plasmas using the observed
line ratios of the He-like ion triplet emission lines can be unreliable,
especially for low-Z ions.Comment: Accepted for publication in Astronomy & Astrophysics, 6 pages, 4
figure
X-ray emission from thin plasmas. Collisional ionization for atoms and ions of H to Zn
Every observation of astrophysical objects involving a spectrum requires
atomic data for the interpretation of line fluxes, line ratios and ionization
state of the emitting plasma. One of the processes which determines it is
collisional ionization. In this study an update of the direct ionization (DI)
and excitation-autoionization (EA) processes is discussed for the H to Zn-like
isoelectronic sequences. In the last years new laboratory measurements and
theoretical calculations of ionization cross sections have become available. We
provide an extension and update of previous published reviews in the
literature. We include the most recent experimental measurements and fit the
cross sections of all individual shells of all ions from H to Zn. These data
are described using an extension of Younger's and Mewe's formula, suitable for
integration over a Maxwellian velocity distribution to derive the subshell
ionization rate coefficients. These ionization rate coefficients are
incorporated in the high-resolution plasma code and spectral fitting tool SPEX
V3.0.Comment: Accepted for publication in A&A, 22 pages, 18 figure
Weak amenability of weighted measure algebras and their second duals
In this paper, we study the weak amenability of weighted measure algebras and
prove that is weakly amenable if and only if is discrete and
every bounded quasi-additive function is inner. We also study the weak
amenability of and and show that the
weak amenability of theses Banach algebras are equivalent to finiteness of .
This gives an answer to the question concerning weak amenability of and
Weak amenability of weighted group algebras
In this paper, we study weak amenability of Beurling algebras. To this end,
we introduce the notion inner quasi-additive functions and prove that for a
locally compact group , the Banach algebra is weakly
amenable if and only if every non-inner quasi-additive function in is unbounded. This provides an answer to the question concerning
weak amenability of and improve some known results in
connection with it
On centralizers of certain Banach algebras
Let be an algebra with a right identity. In this paper, we study centralizers of and show that every centralizer of is a
two-sided centralizer. In the case where, is normed algebra, we also prove
that centralizers of are bounded. Then, we apply the results for
some group algebras and verify that has a nonzero weakly compact centralizer if and only if is compact and the center of is
non-zero. Finally, we investigate Jordan centralizers of and
determine them
Cohomological properties of different types of weak amenability
In this paper, we deal with cohomological properties of weak amenability,
cyclic amenability, cyclic weak amenability and point amenability of Banach
algebras. We look at some hereditary properties of them and show that
continuous homomorphisms with dense range preserve cyclically weak amenability,
however, weak amenability and cyclically amenability are preserved under
certain conditions. We also study these cohomological properties of the
Lau product and the projective tensor product
. Finally, we investigate the cohomological properties of
and establish that cyclically weak amenability of implies
cyclically weak amenability of . This result is true for point amenability
instead of cyclically weak amenability
Products of generalized derivations on rings
In this paper, we show that if the product of generalized
derivations and on an algebra is a generalized
derivation, then and map into . Also, for
generalized derivations and on a prime ring with
characteristic different from two, we give necessary and sufficient conditions
under which is a generalized derivation as well
Chandra imaging of the kpc extended outflow in 1H 0419-577
The Seyfert 1 galaxy 1H 0419-577 hosts a kpc extended outflow that is
evident in the [\ion{O}{iii}] image and that is also detected as a warm
absorber in the UV/X-ray spectrum. Here, we analyze a 30 ks Chandra-ACIS
X-ray image, with the aim of resolving the diffuse extranuclear X-ray emission
and of investigating its relationship with the galactic outflow. Thanks to its
sub-arcsecond spatial resolution, Chandra resolves the circumnuclear X-ray
emission, which extends up to a projected distance of at least 16 kpc
from the center. The morphology of the diffuse X-ray emission is spherically
symmetrical. We could not recover a morphological resemblance between the soft
X-ray emission and the ionization bicone that is traced by the [\ion{O}{iii}]
outflow. we argue that the photoionized gas nebula must be distributed mostly
along the polar directions, outside our line of sight. In this geometry, the
X-ray/UV warm absorber must trace a different gas component, physically
disconnected from the emitting gas, and located closer to the equatorial plane.Comment: accepted for publications A&
Jordan derivations on certain Banach algebras
In this paper, we study the types of Jordan derivations of a Banach algebra
with a right identity . We show that if is commutative and
semisimple, then every Jordan derivation of is a derivation. In this
case, Jordan derivations map into the radical of . We also prove that
every Jordan triple left (right) derivation of is a Jordan left (right)
derivation. Finally, we investigate the range of Jordan left derivations and
establish that every Jordan left derivation of maps into
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