352 research outputs found
Microstructure of the Local Interstellar Cloud and the Identification of the Hyades Cloud
We analyze high-resolution UV spectra of the Mg II h and k lines for 18
members of the Hyades Cluster to study inhomogeneity along these proximate
lines of sight. The observations were taken by the Space Telescope Imaging
Spectrograph (STIS) instrument on board the Hubble Space Telescope (HST). Three
distinct velocity components are observed. All 18 lines of sight show
absorption by the Local Interstellar Cloud (LIC), ten stars show absorption by
an additional cloud, which we name the Hyades Cloud, and one star exhibits a
third absorption component. The LIC absorption is observed at a lower radial
velocity than predicted by the LIC velocity vector derived by Lallement &
Bertin (1992) and Lallement et al. (1995), (v(predicted LIC) - v(observed LIC)
= 2.9 +/- 0.7 km/s), which may indicate a compression or deceleration at the
leading edge of the LIC. We propose an extention of the Hyades Cloud boundary
based on previous HST observations of other stars in the general vicinity of
the Hyades, as well as ground-based Ca II observations. We present our fits of
the interstellar parameters for each absorption component. The availability of
18 similar lines of sight provides an excellent opportunity to study the
inhomogeneity of the warm, partially ionized local interstellar medium (LISM).
We find that these structures are roughly homogeneous. The measured Mg II
column densities do not vary by more than a factor of 2 for angular separations
of < 8 degrees, which at the outer edge of the LIC correspond to physical
separations of < 0.6 pc.Comment: 35 pages, 11 figures, AASTEX v.5.0 plus EPSF extensions in mkfig.sty;
accepted by Ap
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
The Origin of Radio Scintillation In the Local Interstellar Medium
We study three quasar radio sources (B1257-326, B1519-273, and J1819+385)
that show large amplitude intraday and annual scintillation variability
produced by the Earth's motion relative to turbulent-scattering screens located
within a few parsecs of the Sun. We find that the lines of sight to these
sources pass through the edges of partially ionized warm interstellar clouds
where two or more clouds may interact. From the gas flow vectors of these
clouds, we find that the relative radial and transverse velocities of these
clouds are large and could generate the turbulence that is responsible for the
observed scintillation. For all three sight lines the flow velocities of nearby
warm local interstellar clouds are consistent with the fits to the transverse
flows of the radio scintillation signals.Comment: 16 pages, 5 figures; Accepted for publication in Ap
The Ionization of the Local Interstellar Medium, as Revealed by FUSE Observations of N, O and Ar toward White Dwarf Stars
FUSE spectra of the white dwarf stars G191-B2B, GD 394, WD 2211-495 and WD
2331-475 cover the absorption features out of the ground electronic states of N
I, N II, N III, O I and Ar I in the far ultraviolet, providing new insights on
the origin of the partial ionization of the Local Interstellar Medium (LISM),
and for the case of G191-B2B, the interstellar cloud that immediately surrounds
the solar system. Toward these targets the interstellar abundances of Ar I, and
sometimes N I, are significantly below their cosmic abundances relative to H I.
In the diffuse interstellar medium, these elements are not likely to be
depleted onto dust grains. Generally, we expect that Ar should be more strongly
ionized than H (and also O and N whose ionizations are coupled to that of H via
charge exchange reactions) because the cross section for the photoionization of
Ar I is very high. Our finding that Ar I/H I is low may help to explain the
surprisingly high ionization of He in the LISM found by other investigators.
Our result favors the interpretation that the ionization of the local medium is
maintained by a strong EUV flux from nearby stars and hot gases, rather than an
incomplete recovery from a past, more highly ionized condition.Comment: 13 pages, 2 figures. To appear in a special issue of the
Astrophysical Journal Letters devoted to the first scientific results from
the FUSE missio
Organophosphorous neurotoxic antidotes : Pharmacokinetic analysis of avizafone hydrolysis and pralidoxime
Date du colloque : 04/2008</p
Studying the Pulsation of Mira Variables in the Ultraviolet
We present results from an empirical study of the Mg II h & k emission lines
of selected Mira variable stars, using spectra from the International
Ultraviolet Explorer (IUE). The stars all exhibit similar Mg II behavior during
the course of their pulsation cycles. The Mg II flux always peaks after optical
maximum near pulsation phase 0.2-0.5, although the Mg II flux can vary greatly
from one cycle to the next. The lines are highly blueshifted, with the
magnitude of the blueshift decreasing with phase. The widths of the Mg II lines
are also phase-dependent, decreasing from about 70 km/s to 40 km/s between
phase 0.2 and 0.6. We also study other UV emission lines apparent in the IUE
spectra, most of them Fe II lines. These lines are much narrower and not nearly
as blueshifted as the Mg II lines. They exhibit the same phase-dependent flux
behavior as Mg II, but they do not show similar velocity or width variations.Comment: 26 pages, 12 figures; AASTEX v5.0 plus EPSF extensions in mkfig.sty;
to appear in Ap
High-performance liquid chromatography coupled with electrospray tandem mass spectrometry (LC/MS/MS) method for the simultaneous determination of diazepam, atropine and pralidoxime in human plasma
A high-performance liquid chromatography coupled with electrospray tandem mass spectrometry (LC/MS/MS) procedure for the simultaneous determination of diazepam from avizafone, atropine and pralidoxime in human plasma is described. Sample pretreatment consisted of protein precipitation from 100 ÎŒl of plasma using acetonitrile containing the internal standard (diazepam D5). Chromatographic separation was performed on a X-TerraÂź MS C8 column (100 mm Ă 2.1 mm, i.d. 3.5 ÎŒm), with a quick stepwise gradient using a formate buffer (pH 3, 2 mM) and acetonitrile at a flow rate of 0.2 ml/min. The triple quadrupole mass spectrometer was operated in positive ion mode and multiple reaction monitoring was used for drug quantification. The method was validated over the concentration ranges of 1â500 ng/ml for diazepam, 0.25â50 ng/ml for atropine and 5â1000 ng/ml for pralidoxime. The coefficients of variation were always <15% for both intra-day and inter-day precision for each analyte. Mean accuracies were also within ±15%. This method has been successfully applied to a pharmacokinetic study of the three compounds after intramuscular injection of an avizafoneâatropineâpralidoxime combination, in healthy subjects
The Structure of the Local Interstellar Medium V: Electron Densities
We present a comprehensive survey of CII* absorption detections toward stars
within 100 pc in order to measure the distribution of electron densities
present in the local interstellar medium (LISM). Using high spectral resolution
observations of nearby stars obtained by GHRS and STIS onboard the Hubble Space
Telescope, we identify 13 sight lines with 23 individual CII* absorption
components, which provide electron density measurements, the vast majority of
which are new. We employ several strategies to determine more accurate CII
column densities from the saturated CII resonance line, including, constraints
of the line width from the optically thin CII* line, constraints from
independent temperature measurements of the LISM gas based on line widths of
other ions, and third, using measured SII column densities as a proxy for CII
column densities. The sample of electron densities appears consistent with a
log-normal distribution and an unweighted mean value of n_e(CII_SII) =
0.11^+0.10_-0.05 cm^-3. Seven individual sight lines probe the Local
Interstellar Cloud (LIC), and all present a similar value for the electron
density, with a weighted mean of n_e(LIC) = 0.12 +/- 0.04 cm^-3. The Hyades
Cloud, a decelerated cloud at the leading edge of the platoon of LISM clouds,
has a significantly higher electron density than the LIC. Observed toward
G191-B2B, the high electron density may be caused by the lack of shielding from
such a strong radiation source. Given some simple assumptions, the range of
observed electron densities translates into a range of thermal pressures, P/k =
3300^+5500_-1900 K cm^-3. This work greatly expands the number of electron
density measurements and provides important constraints on the ionization,
abundance, and evolutionary models of the local interstellar medium. (abridged)Comment: 41 pages, 9 figures; Accepted for publication in 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
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