753 research outputs found
Ion-by-Ion DEM Determination: I. Method
We describe a technique to derive constraints on the differential emission
measure (DEM) distribution, a measure of the temperature distribution, of
collisionally ionized hot plasmas from their X-ray emission line spectra. This
technique involves fitting spectra using a number of components, each of which
is the entire X-ray line emission spectrum for a single ion. It is applicable
to high-resolution X-ray spectra of any collisionally ionized plasma and
particularly useful for spectra in which the emission lines are broadened and
blended such as those of the winds of hot stars. This method does not require
that any explicit assumptions about the form of the DEM distribution be made
and is easily automated.Comment: This paper was split in two. This version is part I. Part II may be
found at astro-ph/050343
Differential Emission Measure Determination of Collisionally Ionized Plasma: II. Application to Hot Stars
In a previous paper we have described a technique to derive constraints on
the differential emission measure (DEM) distribution, a measure of the
temperature distribution, of collisionally ionized hot plasmas from their X-ray
emission line spectra. We apply this technique to the Chandra/HETG spectra of
all of the nine hot stars available to us at the time this project was
initiated. We find that DEM distributions of six of the seven O stars in our
sample are very similar but that theta Ori has an X-ray spectrum characterized
by higher temperatures. The DEM distributions of both of B stars in our sample
have lower magnitudes than those of the O stars and one, tau Sco, is
characterized by higher temperatures than the other, beta Cru. These results
confirm previous work in which high temperatures have been found for theta Ori
and tau Sco and taken as evidence for channeling of the wind in magnetic
fields, the existence of which are related to the stars' youth. Our results
demonstrate the utility of our method for deriving temperature information for
large samples of X-ray emission line spectra.Comment: The contents of this paper were formerly part of astro-ph/0403603
which was split into two paper
The column density towards LMC X-1
We measure the neutral absorption towards the black hole X-ray binary system
LMC X-1 from six archival soft X-ray spectra obtained with the gratings and/or
CCD detectors on Chandra, XMM-Newton, and Swift. Four spectral models for the
soft continuum have been investigated. While the powerlaw model may
overestimate NH considerably, the others give consistent results. Taking the
lower metalicity of the Large Magellanic Cloud into account, we find equivalent
hydrogen column densities of N_H = (1.0-1.3)*10^22 cm^-2, with a systematic
dependence on the orbital phase. This variation of the neutral absorption can
nearly explain the orbital modulation of the soft X-ray flux recently detected
with the All Sky Monitor (ASM) on the Rossi X-ray Timing Explorer (RXTE).Comment: 4 pages, accepted for publication as a Letter in Astronomy and
Astrophysic
High-Resolution X-ray Spectroscopy of the Interstellar Medium: Structure at the Oxygen Absorption Edge
(Abbrev.) We present high-resolution spectroscopy of the oxygen K-shell
interstellar absorption edge in 7 X-ray binaries using the HETGS onboard
Chandra. Using the brightest sources as templates, we found a best-fit model of
2 absorption edges and 5 Gaussian absorption lines. All of these features can
be explained by the recent predictions of K-shell absorption from neutral and
ionized atomic oxygen. We identify the K alpha and K beta absorption lines from
neutral oxygen, as well as the S=3/2 absorption edge. The expected S=1/2 edge
is not detected in these data due to overlap with instrumental features. We
also identify the K alpha absorption lines from singly and doubly ionized
oxygen. The OI K alpha absorption line is used as a benchmark with which to
adjust the absolute wavelength scale for theoretical predictions of the
absorption cross-sections. We find that shifts of 30-50 mA are required,
consistent with differences previously noticed from comparisons of the theory
with laboratory measurements. Significant oxygen features from dust or
molecular components, as suggested in previous studies, are not required by our
HETGS spectra. With these spectra, we can begin to measure the large-scale
properties of the ISM. We place a limit on the velocity dispersion of the
neutral lines of <200 km s^{-1}, consistent with measurements at other
wavelengths. We also make the first measurement of the oxygen ionization
fractions in the ISM. We constrain the interstellar ratio of OII/OI to ~0.1 and
the ratio of OIII/OI to <0.1.Comment: 12 pages, 8 figures, accepted for publication in the Astrophysical
Journal (Vol. 612, September 1 issue
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