104 research outputs found
OVII and OVIII line emission in the diffuse soft X-ray background: heliospheric and galactic contributions
We study the 0.57 keV (O VII triplet) and 0.65 keV (O VIII) diffuse emission
generated by charge transfer collisions between solar wind (SW) oxygen ions and
interstellar H and He neutral atoms in the inner Heliosphere. These lines which
dominate the 0.3-1.0 keV energy interval are also produced by hot gas in the
galactic halo (GH) and possibly the Local Interstellar Bubble (LB). We
developed a time-dependent model of the SW Charge-Exchange (SWCX) X-ray
emission, based on the localization of the SW Parker spiral at each instant. We
include input SW conditions affecting three selected fields, as well as
shadowing targets observed with XMM-Newton, Chandra and Suzaku and calculate
X-ray emission fot O VII and O VIII lines. We determine SWCX contamination and
residual emission to attribute to the galactic soft X-ray background. We obtain
ground level intensities and/or simulated lightcurves for each target and
compare to X-ray data. The local 3/4 keV emission (O VII and O VIII) detected
in front of shadowing clouds is found to be entirely explained by the CX
heliospheric emission. No emission from the LB is needed at these energies.
Using the model predictions we subtract the heliospheric contribution to the
measured emission and derive the halo contribution. We also correct for an
error in the preliminary analysis of the Hubble Deep Field North (HDFN).Comment: 21 pages (3 on-line), 10 figures (4 on-line), accepted for
publication in Astronomy and Astrophysic
An XMM-Newton Survey of the Soft X-ray Background. II. An All-Sky Catalog of Diffuse O VII and O VIII Emission Intensities
We present an all-sky catalog of diffuse O VII and O VIII line intensities,
extracted from archival XMM observations. The O VII and O VIII intensities are
typically ~2-11 and <~3 ph/cm^2/s/sr (LU), respectively, although much brighter
intensities were also recorded. Our data set includes 217 directions observed
multiple times by XMM. The time variation of the intensities from such
directions may be used to constrain SWCX models. The O VII and O VIII
intensities typically vary by <~5 and <~2 LU between repeat observations,
although several intensity enhancements of >10 LU were observed. We compared
our measurements with SWCX models. The heliospheric SWCX intensity is expected
to vary with ecliptic latitude and solar cycle. We found that the observed
oxygen intensities generally decrease from solar maximum to solar minimum, both
at high ecliptic latitudes (as expected) and at low ecliptic latitudes (not as
expected). The geocoronal SWCX intensity is expected to depend on the solar
wind proton flux and on the sightline's path through the magnetosheath. The
intensity variations seen in directions that have been observed multiple times
are in poor agreement with the predictions of a geocoronal SWCX model. The
oxygen lines account for ~40-50% of the 3/4 keV X-ray background that is not
due to unresolved AGN, in good agreement with a previous measurement. However,
this fraction is not easily explained by a combination of SWCX emission and
emission from hot plasma in the halo. The line intensities tend to increase
with longitude toward the inner Galaxy, possibly due to an increase in the
supernova rate in that direction or the presence of a halo of accreted material
centered on the Galactic Center. The variation of intensity with Galactic
latitude differs in different octants of the sky, and cannot be explained by a
single simple plane-parallel or constant-intensity halo model. (Abridged)Comment: Accepted for publication in the Astrophysical Journal Supplement
Series. 29 pages (main body of paper) plus 85 pages (full versions of Tables
1, 2, and 4 - these tables will be published as machine-readable tables in
the journal, and appear in abbreviated form in the main body of the paper).
12 figures. v2: Minor corrections, conclusions unaltere
SWCX Emission from the Helium Focusing Cone - Model to Data Comparison
A model for heliospheric solar wind charge exchange (SWCX) X-ray emission is applied to a series of XMM-Newton observations of the interplanetary focusing cone of interstellar helium. The X-ray data are from three coupled observations of the South Ecliptic Pole (SEP, to observe the cone) and the Hubble Deep Field-North (HDFN. to monitor global variations of the SWCX emission due to variations in the solar wind) from the period 24 November to 15 December 2003. There is good qualitative agreement between the model predictions and thc data with the maximum SWCX flux observed at an ecliptic longitude of approx. 72deg, consistent with the central longitude of the He cone. We observe a total excess of 2.1 +/- 1.3 LU in the O VII line and 2.0 +/- 0.9 LU in the 0 VIII line. However. the SWCX emission model, which was adjusted for solar wind conditions appropriate for late 2003, predicts an excess from the He cone of only 0.5 LU and 0.2 LU, respectively, in the O VII and O VIII lines. We discuss thc model to data comparison and provide possible explanations for the discrepancies. We also qualitatively reexamine our SWCX n~ocicl predictions in the 1/4 keV band with data from the ROSAT All-Sky Survey towards the North and South Ecliptic Poles, when the He cone was probably first detected in soft X-rays
OVII and OVIII line emission in the diffuse soft X-ray background: heliospheric and galactic contributions
We study the 0.57 keV (O VII triplet) and 0.65 keV (O VIII) diffuse emission
generated by charge transfer collisions between solar wind (SW) oxygen ions and
interstellar H and He neutral atoms in the inner Heliosphere. These lines which
dominate the 0.3-1.0 keV energy interval are also produced by hot gas in the
galactic halo (GH) and possibly the Local Interstellar Bubble (LB). We
developed a time-dependent model of the SW Charge-Exchange (SWCX) X-ray
emission, based on the localization of the SW Parker spiral at each instant. We
include input SW conditions affecting three selected fields, as well as
shadowing targets observed with XMM-Newton, Chandra and Suzaku and calculate
X-ray emission fot O VII and O VIII lines. We determine SWCX contamination and
residual emission to attribute to the galactic soft X-ray background. We obtain
ground level intensities and/or simulated lightcurves for each target and
compare to X-ray data. The local 3/4 keV emission (O VII and O VIII) detected
in front of shadowing clouds is found to be entirely explained by the CX
heliospheric emission. No emission from the LB is needed at these energies.
Using the model predictions we subtract the heliospheric contribution to the
measured emission and derive the halo contribution. We also correct for an
error in the preliminary analysis of the Hubble Deep Field North (HDFN).Comment: 21 pages (3 on-line), 10 figures (4 on-line), accepted for
publication in Astronomy and Astrophysic
Two-component model of the interaction of an interstellar cloud with surrounding hot plasma
We present a two-component gasdynamic model of an interstellar cloud embedded
in a hot plasma. It is assumed that the cloud consists of atomic hydrogen gas,
interstellar plasma is quasineutral. Hydrogen atoms and plasma protons interact
through a charge exchange process. Magnetic felds and radiative processes are
ignored in the model. The influence of heat conduction within plasma on the
interaction between a cloud and plasma is studied. We consider the extreme case
and assume that hot plasma electrons instantly heat the plasma in the
interaction region and that plasma flow can be described as isothermal. Using
the two-component model of the interaction of cold neutral cloud and hot
plasma, we estimate the lifetime of interstellar clouds. We focus on the clouds
typical for the cluster of local interstellar clouds embedded in the hot Local
Bubble and give an estimate of the lifetime of the Local interstellar cloud
where the Sun currently travels. The charge transfer between highly charged
plasma ions and neutral atoms generates X-ray emission. We assume typical
abundance of heavy ions for the Local Bubble plasma and estimate the X-ray
emissivity due to charge exchange from the interface between cold neutral cloud
and hot plasma. Our results show that charge exchange X-ray emission from the
neutral-plasma interfaces can be a non-negligible fraction of the observed
X-ray emission.Comment: 9 pages, 7 figure
Deformations at Earth's dayside magnetopause during quasi-radial IMF conditions: Global kinetic simulations and soft X-ray imaging
The Solar wind Magnetosphere Ionosphere Link Explorer (SMILE) is an ESA-CAS
joint mission. Primary goals are investigating the dynamic response of the
Earth's magnetosphere to the solar wind (SW) impact via simultaneous in situ
magnetosheath (MS) plasma and magnetic field measurements, X-Ray images of the
magnetosheath and magnetic cusps, and UV images of global auroral
distributions. Magnetopause (MP) deformations associated with MS high speed
jets (HSJs) under a quasi-parallel interplanetary magnetic field condition are
studied using a three-dimensional (3-D) global hybrid simulation. Soft X-ray
intensity calculated based on both physical quantities of solar wind proton and
oxygen ions is compared. We obtain key findings concerning deformations at the
MP: (1) MP deformations are highly coherent with the MS HSJs generated at the
quasiparallel region of the bow shock, (2) X-ray intensities estimated using
solar wind H+ and self-consistent O7+ ions are consistent with each other, (3)
Visual spacecraft are employed to check the discrimination ability for
capturing MP deformations on Lunar and polar orbits, respectively. The SMILE
spacecraft on the polar orbit could be expected to provide opportunities for
capturing the global geometry of the magnetopause in the equatorial plane. A
striking point is that SMILE has the potential to capture small-scale MP
deformations and MS transients, such as HSJs, at medium altitudes on its orbit
Distance to the northern high-latitude HI shells
A detailed 3D distribution of interstellar matter in the solar neighborhood
is increasingly necessary. As part of a 3D mapping program, we aim at assigning
a precise distance to the high-latitude HI gas in particular the northern part
(b \geq 55^{circ}) of the shell associated with the conspicuous radio continuum
Loop I. This shell is thought to be the expanding boundary of an interstellar
bubble inflated and recently reheated by the strong stellar winds of the nearby
Scorpius-Centaurus OB. We recorded high-resolution spectra of 30 A-type target
stars located at various distances in the direction of the northern part of
Loop I. Interstellar NaI 5889-5895 and CaII K-H 3934-3968 {\AA} are modeled and
compared with the HI emission spectra from the LAB Survey. About two-thirds of
our stellar spectra possess narrow interstellar lines. Narrow lines are located
at the velocity of the main, low-velocity Loop 1 HI shell ([-6,+1] km/s in the
LSR). Using Hipparcos distances to the target stars, we show that the closest
boundary of the b geq+70^{\circ} part of this low-velocity Loop I arch is
located at of 98 \pm 6 pc. The corresponding interval for the lower-latitude
part (55^{\circ} \leq b \leq 70^{\circ}) is 95-157 pc. However, since the two
structures are apparently connected, the lower limit is more likely. At
variance with this shell, the second HI structure, which is characterized by
LSR Doppler velocities centered at -30 km/s, is NOT detected in any of the
optical spectra. It is located beyond 200 parsecs or totally depleted in NaI
and CaII. We discuss these results in the light of spherical expanding shells
and show that they are difficult to reconcile with simple geometries and a
nearby shell center close to the Plane. Instead, this high-latitude gas seems
to extend the inclined local chimney wall to high distances from the Plane.Comment: Astronomy & Astrophysics (A&A in press
High ions towards white dwarfs: circumstellar line shifts and stellar temperature
Based on a compilation of OVI, CIV, SiIV and NV data from IUE, FUSE, GHRS,
STIS, and COS, we derive an anti- correlation between the stellar temperature
and the high ion velocity shift w.r.t. to the photosphere, with positive (resp.
negative) velocity shifts for the cooler (resp. hotter) white dwarfs. This
trend probably reflects more than a single process, however such a dependence
on the WD's temperature again favors a CS origin for a very large fraction of
those ion absorptions, previously observed with IUE, HST-STIS, HST-GHRS, FUSE,
and now COS, selecting objects for which absorption line radial velocities,
stellar effective temperature and photospheric velocity can be found in the
literature. Interestingly, and gas in near-equilibrium in the star vicinity. It
is also probably significant that the temperature that corresponds to a null
radial velocity, i.e. \simeq 50,000K, also corresponds to the threshold below
which there is a dichotomy between pure or heavy elements atmospheres as well
as some temperature estimates for and a form of balance between radiation
pressure and gravitation. This is consistent with ubiquitous evaporation of
orbiting dusty material. Together with the fact that the fraction of stars with
(red-or blue-) shifted lines and the fraction of stars known to possess heavy
species in their atmosphere are of the same order, such a velocity-temperature
relationship is consistent with quasi-continuous evaporation of orbiting CS
dusty material, followed by accretion and settling down in the photosphere. In
view of these results, ion measurements close to the photospheric or the IS
velocity should be interpreted with caution, especially for stars at
intermediate temperatures. While tracing CS gas, they may be erroneously
attributed to photospheric material or to the ISM, explaining the difficulty of
finding a coherent pattern of the high ions in the local IS 3D distribution.Comment: Accepted by A&A. Body of paper identical to v1. This submission has a
more appropriate truncation of the original abstrac
DXL: a sounding rocket mission for the study of solar wind charge exchange and local hot bubble X-ray emission
The Diffuse X-rays from the Local galaxy (DXL) mission is an approved
sounding rocket project with a first launch scheduled around December 2012. Its
goal is to identify and separate the X-ray emission generated by solar wind
charge exchange from that of the local hot bubble to improve our understanding
of both. With 1,000 cm2 proportional counters and grasp of about 10 cm2 sr both
in the 1/4 and 3/4 keV bands, DXL will achieve in a 5-minute flight what cannot
be achieved by current and future X-ray satellites.Comment: 15 Pages, 5 figures. Accepted for publication on Experimental
Astronom
- …