120,927 research outputs found
Interstellar Dust Close to the Sun
The low density interstellar medium (ISM) close to the Sun and inside of the
heliosphere provides a unique laboratory for studying interstellar dust grains.
Grain characteristics in the nearby ISM are obtained from observations of
interstellar gas and dust inside of the heliosphere and the interstellar gas
towards nearby stars. Comparison between the gas composition and solar
abundances suggests that grains are dominated by olivines and possibly some
form of iron oxide. Measurements of the interstellar Ne/O ratio by the
Interstellar Boundary Explorer spacecraft indicate that a high fraction of
interstellar oxygen in the ISM must be depleted onto dust grains. Local
interstellar abundances are consistent with grain destruction in ~150 km/s
interstellar shocks, provided that the carbonaceous component is hydrogenated
amorphous carbon and carbon abundances are correct. Variations in relative
abundances of refractories in gas suggest variations in the history of grain
destruction in nearby ISM. The large observed grains, > 1 micron, may indicate
a nearby reservoir of denser ISM. Theoretical three-dimensional models of the
interaction between interstellar dust grains and the solar wind predict that
plumes of about 0.18 micron dust grains form around the heliosphere.Comment: 2011 AGOS Taiwan meeting; accepted for publication in Earth, Planets
and Spac
Properties of interstellar wind leading to shape morphology of the dust surrounding HD 61005
A structure formed by dust particles ejected from the debris ring around HD
61005 is observed in the scattered light. The main aim here is to constrain
interstellar wind parameters that lead to shape morphology in the vicinity of
HD 61005 using currently available observational data for the debris ring.
Equation of motion of 2 10 dust particles ejected from the debris
ring under the action of the electromagnetic radiation, stellar wind, and
interstellar wind is solved. A two-dimensional (2D) grid is placed in a given
direction for accumulation of the light scattered on the dust particles in
order to determine the shape morphology. The interaction of the interstellar
wind and the stellar wind is considered. Groups of unknown properties of the
interstellar wind that create the observed morphology are determined. A
relation between number densities of gas components in the interstellar wind
and its relative velocity is found. Variations of the shape morphology caused
by the interaction with the interstellar clouds of various temperatures are
studied. When the interstellar wind velocity is tilted from debris ring axis a
simple relation between the properties of the interstellar wind and an angle
between the line of sight and the interstellar wind velocity exists. Dust
particles that are most significantly influenced by stellar radiation move on
the boundary of observed structure. Observed structure at HD 61005 can be
explained as a result of dust particles moving under the action of the
interstellar wind. Required number densities or velocities of the interstellar
wind are much higher than that of the interstellar wind entering the Solar
system.Comment: 11 pages, 7 figures, accepted to A&
Orbital evolution under the action of fast interstellar gas flow with non-constant drag coefficient
The acceleration of a spherical dust particle caused by an interstellar gas
flow depends on the drag coefficient which is, for the given particle and flow
of interstellar gas, a specific function of the relative speed of the dust
particle with respect to the interstellar gas. We investigate the motion of a
dust particle in the case when the acceleration caused by the interstellar gas
flow represent a small perturbation to the gravity of a central star. We
present the secular time derivatives of the Keplerian orbital elements of the
dust particle under the action of the acceleration from the interstellar gas
flow for arbitrary orbit orientation. The semimajor axis of the dust particle
is a decreasing function of time for an interstellar gas flow acceleration with
constant drag coefficient and also for such an acceleration with the linearly
variable drag coefficient. The decrease of the semimajor axis is slower for the
interstellar gas flow acceleration with the variable drag coefficient. The
minimal and maximal values of the decrease of the semimajor axis are
determined. In the planar case, when the interstellar gas flow velocity lies in
the orbital plane of the particle, the orbit always approaches the position
with the maximal value of the transversal component of the interstellar gas
flow velocity vector measured at perihelion.
The properties of the orbital evolution derived from the secular time
derivatives are consistent with numerical integrations of the equation of
motion. If the interstellar gas flow speed is much larger than the speed of the
dust particle, then the linear approximation of dependence of the drag
coefficient on the relative speed of the dust particle with respect to the
interstellar gas is usable for practically arbitrary (no close to zero) values
of the molecular speed ratios (Mach numbers).Comment: 12 pages, 6 figures, 2 equations added in v
Assessment of detectability of neutral interstellar deuterium by IBEX observations
The abundance of deuterium in the interstellar gas in front of the Sun gives
insight into the processes of filtration of neutral interstellar species
through the heliospheric interface and potentially into the chemical evolution
of the Galactic gas. We investigate the possibility of detection of neutral
interstellar deuterium at 1 AU from the Sun by direct sampling by the
Interstellar Boundary Explorer (IBEX). We simulate the flux of neutral
interstellar D at IBEX for the actual measurement conditions. We assess the
number of interstellar D atom counts expected during the first three years of
IBEX operation. We also simulate observations expected during an epoch of high
solar activity. In addition, we calculate the expected counts of D atoms from
the thin terrestrial water layer, sputtered from the IBEX-Lo conversion surface
by neutral interstellar He atoms. Most D counts registered by IBEX-Lo are
expected to originate from the water layer, exceeding the interstellar signal
by 2 orders of magnitude. However, the sputtering should stop once the Earth
leaves the portion of orbit traversed by interstellar He atoms. We identify
seasons during the year when mostly the genuine interstellar D atoms are
expected in the signal. During the first 3 years of IBEX operations about 2
detectable interstellar D atoms are expected. This number is comparable with
the expected number of sputtered D atoms registered during the same time
intervals. The most favorable conditions for the detection occur during low
solar activity, in an interval including March and April each year. The
detection chances could be improved by extending the instrument duty cycle,
e.g., by making observations in the special deuterium mode of IBEX-Lo.Comment: Accepted for Astronomy & Astrophysic
Centrosymmetric molecules as possible carriers of diffuse interstellar bands
In this paper, we present new data with interstellar C2 (Phillips bands A-X),
from observations made with the Ultraviolet-Visual Echelle Spectrograph of the
European Southern Observatory. We have determined the interstellar column
densities and excitation temperatures of C2 for nine Galactic lines. For seven
of these, C2 has never been observed before, so in this case the still small
sample of interstellar clouds (26 lines of sight), where a detailed analysis of
C2 excitation has been made, has increased significantly. This paper is a
continuation of previous works where interstellar molecules (C2 and diffuse
interstellar bands) have been analysed. Because the sample of interstellar
clouds with C2 has increased, we can show that the width and shape of the
profiles of some diffuse interstellar bands (6196 and 5797 A) apparently depend
on the gas kinetic and rotational temperatures of C2; the profiles are broader
because of the higher values of the gas kinetic and rotational temperatures of
C2. There are also diffuse interstellar bands (4964 and 5850 A) for which this
effect does not exist.Comment: 8 pages, 4 figures, accepted to MNRAS 201
Dust in the Local Interstellar Wind
The gas-to-dust mass ratios found for interstellar dust within the Solar
System, versus values determined astronomically for the cloud around the Solar
System, suggest that large and small interstellar grains have separate
histories, and that large interstellar grains preferentially detected by
spacecraft are not formed exclusively by mass exchange with nearby interstellar
gas. Observations by the Ulysses and Galileo satellites of the mass spectrum
and flux rate of interstellar dust within the heliosphere are combined with
information about the density, composition, and relative flow speed and
direction of interstellar gas in the cloud surrounding the solar system to
derive an in situ value for the gas-to-dust mass ratio, . Hubble observations of the cloud surrounding the solar system
yield a gas-to-dust mass ratio of Rg/d=551+61-251 when B-star reference
abundances are assumed. The exclusion of small dust grains from the heliosheath
and heliosphere regions are modeled, increasing the discrepancy between
interstellar and in situ observations. The shock destruction of interstellar
grains is considered, and comparisons are made with interplanetary and presolar
dust grains.Comment: 87 pages, 9 figures, 6 tables, accepted for publication in
Astrophysical Journal. Uses AASTe
Perspectives on Interstellar Dust Inside and Outside of the Heliosphere
Measurements by dust detectors on interplanetary spacecraft appear to
indicate a substantial flux of interstellar particles with masses exceeding
10^{-12}gram. The reported abundance of these massive grains cannot be typical
of interstellar gas: it is incompatible with both interstellar elemental
abundances and the observed extinction properties of the interstellar dust
population. We discuss the likelihood that the Solar System is by chance
located near an unusual concentration of massive grains and conclude that this
is unlikely, unless dynamical processes in the ISM are responsible for such
concentrations. Radiation pressure might conceivably drive large grains into
"magnetic valleys". If the influx direction of interstellar gas and dust is
varying on a ~10 yr timescale, as suggested by some observations, this would
have dramatic implications for the small-scale structure of the interstellar
medium.Comment: 13 pages. To appear in Space Science Review
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