190 research outputs found
The High-Velocity Outflow of PG1211+143 May Not be That Fast
We analyze the X-ray spectrum of the quasar PG1211+143 observed with the CCD
and grating spectrometers on board XMM-Newton. Using an ion by ion fitting
model we find an outflow component of about 3000 km/s that includes absorption
lines of K-shell and L-shell ions of the astrophysically abundant elements. We
also identify and include in our model broad (FWHM = 6000 km/s) emission lines
from H-like ions of C, N, O, and Ne, and He-like ions of O, Ne, and Mg. The
outflow velocity we find is an alternative interpretation of the data and is in
contrast with the ultra high velocity of ~24000 km/s reported previously for
this object. Nevertheless, we can not completely rule out the presence of a
high velocity component due to the poor signal-to-noise ratio of the data.Comment: 7 pages, 2 figures, emulateapj, accepted for publication in The
Astrophysical Journa
Is The Fe M-shell Absorber Part of The Outflow in Active Galactic Nuclei?
The X-ray emission of many active galactic nuclei (AGNs) is absorbed between
15 and 17 Angstrom by means of unresolved (inner-shell) transition arrays
(UTAs) of Fe M-shell ions. The outflow velocities implied by the Doppler shifts
of the individual UTAs in the spectrum have never before been measured. Thus,
the Fe-M absorber has been commonly assumed to be part of the ionized AGN
outflow, whose velocities are readily obtained from more easily measured
spectral lines. The best spectrum of Fe-M absorption is available from the
integrated 900 ks Chandra HETGS observations of NGC 3783, in which some Fe-M
ions are clearly resolved. We measure the velocities of the individual Fe-M
ions in NGC 3783 for the first time. Surprisingly, we find that the Fe-M
absorber, most noticeably Fe, Fe, and Fe, is not
outflowing at the same velocity as the previously known wind. In fact, it
appears to be stationary and therefore not part of the outflow at all. It
could, alternatively, be ascribed to the skin of the dusty torus. This reduces
appreciably the mass loss rate estimated for the NGC 3783 outflow and perhaps
for other similar sources as well, in which the various Fe-M ions are not
resolved.Comment: To be published in Ap
Coronae of Stars with Super Solar Elemental Abundances
Coronal elemental abundances are known to deviate from the photospheric
values of their parent star, with the degree of deviation depending on the
First Ionization Potential (FIP). This study focuses on the coronal composition
of stars with super-solar photospheric abundances. We present the coronal
abundances of six such stars: 11 LMi, Hor, HR 7291, Boo, and
Cen A and B. These stars all have high-statistics X-ray spectra, three
of which are presented for the first time. The abundances measured in this
paper are obtained using the line-resolved spectra of the Reflection Grating
Spectrometer (RGS) in conjunction with the higher throughput EPIC-pn camera
spectra on board the XMM-Newton observatory. A collisionally ionized plasma
model with two or three temperature components is found to represent the
spectra well. All elements are found to be consistently depleted in the coronae
compared to their respective photospheres. For 11 LMi and Boo no FIP
effect is present, while Hor, HR 7291, and Cen A and B show a
clear FIP trend. These conclusions hold whether the comparison is made with
solar abundances or the individual stellar abundances. Unlike the solar corona
where low FIP elements are enriched, in these stars the FIP effect is
consistently due to a depletion of high FIP elements with respect to actual
photospheric abundances. Comparing to solar abundances (instead of stellar)
yields the same fractionation trend as on the Sun. In both cases a similar FIP
bias is inferred, but different fractionation mechanisms need to be invoked.Comment: 11 pages, 7 figures, submitted to A&A. Comments are welcom
X-Ray Emission from Planetary Nebulae Calculated by 1D Spherical Numerical Simulations
We calculate the X-ray emission from both constant and time evolving shocked
fast winds blown by the central stars of planetary nebulae (PNs) and compare
with observations. Using spherically symmetric numerical simulations with
radiative cooling, we calculate the flow structure, and the X-ray temperature
and luminosity of the hot bubble formed by the shocked fast wind. We find that
a constant fast wind gives results that are very close to those obtained from
the self-similar solution. We show that in order for a fast shocked wind to
explain the observed X-ray properties of PNs, rapid evolution of the wind is
essential. More specifically, the mass loss rate of the fast wind should be
high early on when the speed is ~300-700 km/s, and then it needs to drop
drastically by the time the PN age reaches ~1000 yr. This implies that the
central star has a very short pre-PN (post-AGB) phase.Comment: accepted to MNRA
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