473 research outputs found
Neutral interstellar hydrogen in the inner heliosphere under the influence of wavelength-dependent solar radiation pressure
With the plethora of detailed results from heliospheric missions and at the
advent of the first mission dedicated IBEX, we have entered the era of
precision heliospheric studies. Interpretation of these data require precision
modeling, with second-order effects quantitatively taken into account. We study
the influence of the non-flat shape of the solar Ly-alpha line on the
distribution of neutral interstellar H in the inner heliosphere. Based on
available data, we (i) construct a model of evolution for the solar Ly-alpha
line profile with solar activity, (ii) modify an existing test-particle code
used to calculate the distribution of neutral interstellar H in the inner
heliosphere so that it takes the dependence of radiation pressure on radial
velocity into account, and (iii) compare the results of the old and new
version. Discrepancies between the classical and Doppler models appear between
~5 and ~3 AU and increase towards the Sun from a few percent to a factor of 1.5
at 1 AU. The classical model overestimates the density everywhere except for a
~60-degr cone around the downwind direction, where a density deficit appears.
The magnitude of the discrepancies appreciably depends on the phase of the
solar cycle, but only weakly on the parameters of the gas at the termination
shock. For in situ measurements of neutral atoms performed at ~1 AU, the
Doppler correction will need to be taken into account, because the
modifications include both the magnitude and direction of the local flux by a
few km/s and degrees, respectively, which, when unaccounted for, would
introduce an error of a few km/s and degrees in determination of the magnitude
and direction of the bulk velocity vector at the termination shock.Comment: 10 pages, 13 figures, accepted by A&
The Velocity Distribution of the Nearest Interstellar Gas
The bulk flow velocity for the cluster of interstellar cloudlets within about
30 pc of the Sun is determined from optical and ultraviolet absorption line
data, after omitting from the sample stars with circumstellar disks or variable
emission lines and the active variable HR 1099. Ninety-six velocity components
towards the remaining 60 stars yield a streaming velocity through the local
standard of rest of -17.0+/-4.6 km/s, with an upstream direction of l=2.3 deg,
b=-5.2 deg (using Hipparcos values for the solar apex motion). The velocity
dispersion of the interstellar matter (ISM) within 30 pc is consistent with
that of nearby diffuse clouds, but present statistics are inadequate to
distinguish between a Gaussian or exponential distribution about the bulk flow
velocity. The upstream direction of the bulk flow vector suggests an origin
associated with the Loop I supernova remnant. Groupings of component velocities
by region are seen, indicating regional departures from the bulk flow velocity
or possibly separate clouds. The absorption components from the cloudlet
feeding ISM into the solar system form one of the regional features. The
nominal gradient between the velocities of upstream and downstream gas may be
an artifact of the Sun's location near the edge of the local cloud complex. The
Sun may emerge from the surrounding gas-patch within several thousand years.Comment: Typographical errors corrected; Five tables, seven figures;
Astrophysical Journal, in pres
End-to end simulations of LINAC4
Linac4 is a new H- linear accelerator presently studied at CERN. This machine consists of normal-conducting structures operating at 352.2 MHz and 704.4 MHz re-using the RF equipment from the decommissioned LEP collider. It consists of a 95 keV H- source, a 352 MHz RFQ bringing the energy the energy to 3 MeV, a Chopper line, a 352 MHz Drift Tube Linac bringing the energy to 40 MeV, a 352 MHz Coupled Cavity Drift Tube Linac bringing the energy to 90 MeV and a 704 MHz Side Coupled Linac bringing the energy to 160 MeV. Each section is designed and optimized as stand-alone machines for a good transmission and minimum possible emittance growth. End-to-end simulations starting from the RFQ have been carried out in order to validate and compare the multiparticle simulation codes PATH Manager and TRACEWIN used for beam dynamics calculations as well as to perform a global optimization of the structures in the context of a complex machine
Deuterium Toward WD1634-573: Results from the Far Ultraviolet Spectroscopic Explorer (FUSE) Mission
We use Far Ultraviolet Spectrocopic Explorer (FUSE) observations to study
interstellar absorption along the line of sight to the white dwarf WD1634-573
(d=37.1+/-2.6 pc). Combining our measurement of D I with a measurement of H I
from Extreme Ultraviolet Explorer data, we find a D/H ratio toward WD1634-573
of D/H=(1.6+/-0.5)e-5. In contrast, multiplying our measurements of D I/O
I=0.035+/-0.006 and D I/N I=0.27+/-0.05 with published mean Galactic ISM gas
phase O/H and N/H ratios yields D/H(O)=(1.2+/-0.2)e-5 and
D/H(N)=(2.0+/-0.4)e-5, respectively. Note that all uncertainties quoted above
are 2 sigma. The inconsistency between D/H(O) and D/H(N) suggests that either
the O I/H I and/or the N I/H I ratio toward WD1634-573 must be different from
the previously measured average ISM O/H and N/H values. The computation of
D/H(N) from D I/N I is more suspect, since the relative N and H ionization
states could conceivably vary within the LISM, while the O and H ionization
states will be more tightly coupled by charge exchange.Comment: 23 pages, 5 figures; AASTEX v5.0 plus EPSF extensions in mkfig.sty;
accepted by ApJ Supplemen
Elemental Abundances and Ionization States within the Local Interstellar Cloud Derived from HST and FUSE Observations of the Capella Line of Sight
We use ultraviolet spectra of Capella from the Hubble Space Telescope (HST)
and Far Ultraviolet Spectroscopic Explorer (FUSE) satellites to study
interstellar absorption lines from the Local Interstellar Cloud (LIC).
Measurements of these lines are used to empirically determine the ionization
states of carbon, nitrogen, and silicon in the LIC, for comparison with the
predictions of theoretical photoionization models. We find that the observed
ionization states are consistent with previously published photoionization
predictions. Total abundances are determined for the elements mentioned above,
and others, for comparison with solar abundances. Magnesium, aluminum, silicon,
and iron are all depleted by at least a factor of 10 toward Capella. The
abundances of carbon, nitrogen, and oxygen are essentially solar, although the
error bars are large enough to also allow depletions of about a factor of 2 for
these elements.Comment: 31 pages, 10 figures; AASTEX v5.0 plus EPSF extensions in mkfig.sty;
accepted by Ap
Stellar Lyman-alpha Emission Lines in the Hubble Space Telescope Archive: Intrinsic Line Fluxes and Absorption from the Heliosphere and Astrospheres
We search the Hubble Space Telescope (HST) archive for previously unanalyzed
observations of stellar H I Lyman-alpha emission lines, our primary purpose
being to look for new detections of Lyman-alpha absorption from the outer
heliosphere, and to also search for analogous absorption from the astrospheres
surrounding the observed stars. The astrospheric absorption is of particular
interest because it can be used to study solar-like stellar winds that are
otherwise undetectable. We find and analyze 33 HST Lyman-alpha spectra in the
archive. All the spectra were taken with the E140M grating of the Space
Telescope Imaging Spectrograph (STIS) instrument on board HST. The HST/STIS
spectra yield 4 new detections of heliospheric absorption (70 Oph, Xi Boo, 61
Vir, and HD 165185) and 7 new detections of astrospheric absorption (EV Lac, 70
Oph, Xi Boo, 61 Vir, Delta Eri, HD 128987, and DK UMa), doubling the previous
number of heliospheric and astrospheric detections. When combined with previous
results, 10 of 17 lines of sight within 10 pc yield detections of astrospheric
absorption. This high detection fraction implies that most of the ISM within 10
pc must be at least partially neutral, since the presence of H I within the ISM
surrounding the observed star is necessary for an astrospheric detection. In
contrast, the detection percentage is only 9.7% (3 out of 31) for stars beyond
10 pc. Our Lyman-alpha analyses provide measurements of ISM H I and D I column
densities for all 33 lines of sight, and we discuss some implications of these
results. Finally, we measure chromospheric Lyman-alpha fluxes from the observed
stars. We use these fluxes to determine how Lyman-alpha flux correlates with
coronal X-ray and chromospheric Mg II emission, and we also study how
Lyman-alpha emission depends on stellar rotation.Comment: 56 pages, 15 figures; AASTEX v5.0 plus EPSF extensions in mkfig.sty;
accepted by ApJ
Regular obstructed categories and TQFT
A proposal of the concept of -regular obstructed categories is given. The
corresponding regularity conditions for mappings, morphisms and related
structures in categories are considered. An n-regular TQFT is introduced. It is
shown the connection of time reversibility with the regularity.Comment: 22 pages in Latex. To be published in J. Math. Phy
Local ISM 3D Distribution and Soft X-ray Background Inferences for Nearby Hot Gas
Three-dimensional (3D) interstellar medium (ISM) maps can be used to locate not only interstellar (IS) clouds, but also IS bubbles between the clouds that are blown by stellar winds and supernovae, and are filled by hot gas. To demonstrate this, and to derive a clearer picture of the local ISM, we compare our recent 3D IS dust distribution maps to the ROSAT diffuse Xray background maps after removal of heliospheric emission. In the Galactic plane, there is a good correspondence between the locations and extents of the mapped nearby cavities and the soft (0.25 keV) background emission distribution, showing that most of these nearby cavities contribute to this soft X-ray emission. Assuming a constant dust to gas ratio and homogeneous 106 K hot gas filling the cavities, we modeled in a simple way the 0.25 keV surface brightness along the Galactic plane as seen from the Sun, taking into account the absorption by the mapped clouds. The data-model comparison favors the existence of hot gas in the solar neighborhood, the so-called Local Bubble (LB). The inferred mean pressure in the local cavities is found to be approx.9,400/cu cm K, in agreement with previous studies, providing a validation test for the method. On the other hand, the model overestimates the emission from the huge cavities located in the third quadrant. Using CaII absorption data, we show that the dust to CaII ratio is very small in those regions, implying the presence of a large quantity of lower temperature (non-X-ray emitting) ionized gas and as a consequence a reduction of the volume filled by hot gas, explaining at least part of the discrepancy. In the meridian plane, the two main brightness enhancements coincide well with the LB's most elongated parts and chimneys connecting the LB to the halo, but no particular nearby cavity is found towards the enhancement in the direction of the bright North Polar Spur (NPS) at high latitude. We searched in the 3D maps for the source regions of the higher energy (0.75 keV) enhancements in the fourth and first quadrants. Tunnels and cavities are found to coincide with the main bright areas, however no tunnel nor cavity is found to match the low-latitude b > or approx. 8deg, brightest part of the NPS. In addition, the comparison between the 3D maps and published spectral data favors a NPS central source region location beyond 230 pc, i.e. at larger distance than usually considered. Those examples illustrate the potential use of more detailed 3D distributions of the nearby ISM for the interpretation of the diffuse soft X-ray background
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
The D/H Ratio in Interstellar Gas Towards G191-B2B
We reinvestigate the question of spatial variation of the local D/H
abundance, using both archival GHRS spectra, and new echelle spectra of
G191-B2B obtained with the Space Telescope Imaging Spectrograph (STIS) aboard
HST. Our analysis uses stratified line-blanketed non-LTE model atmosphere
calculations to determine the shape of the intrinsic WD Lyman-alpha profile and
estimate the WD photospheric contamination of the interstellar lines. Although
three velocity components were reported previously towards G191-B2B, we detect
only two velocity components. The first component is at V(hel) ~ 8.6 km/s and
the second at V(hel) ~ 19.3 km/s, which we identify with the Local Interstellar
Cloud (LIC). From the STIS data we derive D/H = 1.60(+0.39,-0.27)X10^-5 for the
LIC component, and D/H > 1.26X10^-5 for the 8.6 km/s component (uncertainties
denote 2-sigma or 95% confidence limits). The STIS data provide no evidence for
local or component-to-component variation in the D/H ratio. Despite using two
velocity components for the profile fitting and using a more physically
realistic WD Lyman-alpha profile for G191-B2B, our re-analysis of the GHRS data
indicates a component-to-component variation as well as a variation of the D/H
ratio in the LISM, neither of which are supported by the newer STIS data. We
believe the most probable cause for this difference is the characterization of
the background due to scattered light in the GHRS and STIS spectrographs. The
two-dimensional MAMA detectors of STIS measure both the spatial and wavelength
dependences of scattered light, allowing more accurate scattered light
corrections than was possible with GHRS.Comment: Accepted for publication in Astrophysical Journal Letters. 10 pages +
3 figures. (Abstract is abridged.
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