200 research outputs found
X-ray narrow line region variability as a geometry probe: The case of NGC 5548
We study the long time scale variability of the gas responsible for the X-ray
narrow emission lines in the Seyfert 1 galaxy NGC 5548, in order to constrain
the location and geometry of the emitting gas. Using X-ray spectra taken with
the Chandra-LETGS and HETGS instruments and with XMM-Newton RGS and combining
them with long-term monitoring observations of the Rossi X-ray Timing Explorer
(RXTE), we perform a correlation analysis in order to try constrain the time
scale on which the narrow line emitting gas responds to variations of the
continuum flux. With the inclusion of the 2007 Chandra-LETGS observation we
have an additional observation at an historically low flux level. We conclude
that the NLR in NGC 5548 is in the form of an ionization cone, compact in size,
and located between 1 and 15 pc from the central source, depending on the exact
geometry of the NLR.Comment: 6 pages, 4 figures, accepted for publication in A&
The outflow in Mrk 509: A method to calibrate XMM-Newton EPIC-pn and RGS
We have analyzed three XMM-Newton observations of the Seyfert 1 galaxy Mrk
509, with the goal to detect small variations in the ionized outflow
properties. Such measurements are limited by the quality of the
cross-calibration between RGS, the best instrument to characterize the
spectrum, and EPIC-pn, the best instrument to characterize the variability. For
all three observations we are able to improve the relative calibration of RGS
and pn consistently to 4 %. In all observations we detect three different
outflow components and, thanks to our accurate cross-calibration we are able to
detect small differences in the ionization parameter and column density in the
highest ionized component of the outflow. This constrains the location of this
component of the outflow to within 0.5 pc of the central source. Our method for
modeling the relative effective area is not restricted to just this source and
can in principle be extended to other types of sources as well.Comment: 11 pages, 9 figure
Light elements in massive single and binary stars
We highlight the role of the light elements (Li, Be, B) in the evolution of
massive single and binary stars, which is largely restricted to a diagnostic
value, and foremost so for the element boron. However, we show that the boron
surface abundance in massive early type stars contains key information about
their foregoing evolution which is not obtainable otherwise. In particular, it
allows to constrain internal mixing processes and potential previous mass
transfer event for binary stars (even if the companion has disappeared). It may
also help solving the mystery of the slowly rotating nitrogen-rich massive main
sequence stars.Comment: 10 pages, 8 figures, to appear in proc. IAU-Symp. 268. C. Charbonnel
et al., eds
Multiwavelength campaign on Mrk 509. V. Chandra-LETGS observation of the ionized absorber
We present here the results of a 180 ks Chandra-LETGS observation as part of
a large multi-wavelength campaign on Mrk 509. We study the warm absorber in Mrk
509 and use the data from a simultaneous HST-COS observation in order to assess
whether the gas responsible for the UV and X-ray absorption are the same. We
analyzed the LETGS X-ray spectrum of Mrk 509 using the SPEX fitting package. We
detect several absorption features originating in the ionized absorber of the
source, along with resolved emission lines and radiative recombination
continua. The absorption features belong to ions with, at least, three distinct
ionization degrees. The lowest ionized component is slightly redshifted (v =
+73 km/s) and is not in pressure equilibrium with the others, and therefore it
is not likely part of the outflow, possibly belonging to the interstellar
medium of the host galaxy. The other components are outflowing at velocities of
-196 and -455 km/s, respectively. The source was observed simultaneously with
HST-COS, finding 13 UV kinematic components. At least three of them can be
kinematically associated with the observed X-ray components. Based on the
HST-COS results and a previous FUSE observation, we find evidence that the UV
absorbing gas might be co-located with the X-ray absorbing gas and belong to
the same structure.Comment: 12 pages, 7 figures, 9 tables. Accepted for publication in Astronomy
& Astrophysic
The warm absorber in NGC 5548: The lean years
We study the variability of the warm absorber and the gas responsible for the
emission lines in the Seyfert 1 galaxy NGC 5548, in order to constrain the
location and physical properties of these components. Using X-ray spectra taken
with the \textit{Chandra}LETGS in 2002 and 2005, we study variability in the
ionic column densities and line intensities. We find a lower \ion{O}{vii}
forbidden emission line flux in 2005, while the Fe K line flux stays
constant. The warm absorber is less ionized in 2005, allowing us to constrain
its location to within 7 pc of the central source. Using both the observed
variability and the limit on the FWHM of the \ion{O}{vii} f line, we have
constrained the location of the narrow line region to a distance of 1 pc from
the central source. The apparent lack of variability of the Fe K line
flux does not allow for a unique explanation.Comment: 6 pages, 6 figures, accepted by A&
Gamma-Ray Bursts from tidally spun-up Wolf-Rayet stars?
The collapsar model requires rapidly rotating Wolf-Rayet stars as progenitors
of long gamma-ray bursts. However, Galactic Wolf-Rayet stars rapidly lose
angular momentum due to their intense stellar winds. We investigate whether the
tidal interaction of a Wolf-Rayet star with a compact object in a binary system
can spin up the Wolf-Rayet star enough to produce a collapsar. We compute the
evolution of close Wolf-Rayet binaries, including tidal angular momentum
exchange, differential rotation of the Wolf-Rayet star, internal magnetic
fields, stellar wind mass loss, and mass transfer. The Wolf-Rayet companion is
approximated as a point mass. We then employ a population synthesis code to
infer the occurrence rates of the various relevant binary evolution channels.
We find that the simple scenario -- i.e., the Wolf-Rayet star being tidally
spun up and producing a collapsar -- does not occur at solar metallicity and
may only occur with low probability at low metallicity. It is limited by the
widening of the binary orbit induced by the strong Wolf-Rayet wind or by the
radius evolution of the Wolf-Rayet star that most often leads to a binary
merger. The tidal effects enhance the merger rate of Wolf-Rayet stars with
black holes such that it becomes comparable to the occurrence rate of long
gamma-ray bursts.Comment: 9 pages, 11 figures, accepted for publication in A&
A phenomenological model for the X-ray spectrum of Nova V2491 Cygni
The X-ray flux of Nova V2491 Cyg reached a maximum some forty days after
optical maximum. The X-ray spectrum at that time, obtained with the RGS of
XMM-Newton, shows deep, blue-shifted absorption by ions of a wide range of
ionization. We show that the deep absorption lines of the X-ray spectrum at
maximum, and nine days later, are well described by the following
phenomenological model with emission from a central blackbody and from a
collisionally ionized plasma (CIE). The blackbody spectrum (BB) is absorbed by
three main highly-ionized expanding shells; the CIE and BB are absorbed by cold
circumstellar and interstellar matter that includes dust. The outflow density
does not decrease monotonically with distance. The abundances of the shells
indicate that they were ejected from an O-Ne white dwarf. We show that the
variations on time scales of hours in the X-ray spectrum are caused by a
combination of variation in the central source and in the column density of the
ionized shells. Our phenomenological model gives the best description so far of
the supersoft X-ray spectrum of nova V2491 Cyg, but underpredicts, by a large
factor, the optical and ultraviolet flux. The X-ray part of the spectrum must
originate from a very different layer in the expanding envelope, presumably
much closer to the white dwarf than the layers responsible for the
optical/ultraviolet spectrum. This is confirmed by absence of any correlation
between the X-ray and UV/optical observed fluxes.Comment: 11 pages, 6 figure
Опухоли с невыявленным первичным очагом: современные подходы к лечению
Представлены современные методы и схемы лечения разных видов рака с невыясненным очагом и получаемые результаты.Contemporary methods of treatment of various types of cancer with unrevealed focus as well as the obtained results are described
Isolation of a novel aquaglyceroporin from a marine teleost (Sparus auratus) Function and tissue distribution
The aquaporins (formerly called the major intrinsic
protein family) are transmembrane channel proteins. The
family includes the CHIP group, which are functionally
characterised as water channels and the GLP group,
which are specialised for glycerol transport. The present
study reports the identification and characterisation of a
novel GLP family member in a teleost fish, the sea bream
Sparus auratus. A sea bream aquaporin (sbAQP) cDNA of
1047·bp and encoding a protein of 298·amino acids was
isolated from a kidney cDNA library. Functional
characterization of the sbAQP using a Xenopus oocyte
assay revealed that the isolated cDNA stimulated osmotic
water permeability in a mercury-sensitive manner and
also stimulated urea and glycerol uptake. Northern
blotting demonstrated that sbAQP was expressed at high
levels in the posterior region of the gut, where two transcripts were identified (1.6·kb and 2·kb), and in
kidney, where a single transcript was present (2·kb). In
situ hybridisation studies with a sbAQP riboprobe
revealed its presence in the lamina propria and smooth
muscle layer of the posterior region of the gut and in
epithelial cells of some kidney tubules. sbAQP was also
present in putative chloride cells of the gill. Phylogenetic
analysis of sbAQP, including putative GLP genes from
Fugu rubripes, revealed that it did not group with any of
the previously isolated vertebrate GLPs and instead
formed a separate group, suggesting that it may be a novel
GLP member.This work was supported by project PRAXIS
XXI/2/2.1/BIA/211/94 from the Portuguese National Science
and Technology Foundation (FCT), co-financed by EU
structural funds, DG-Fisheries Project Q5RS-2002-00784
(CRYOCYTE) and an EU Biotech grant (QLRT2000-00778).
C.R.A.S., J.C.R.C. and J.F. were in receipt of FCT
fellowships PRAXIS XXI/BPD/22040/99, PRAXIS
XXI/BD/19925/99BPD/22033/99, respectively
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