10 research outputs found
Silicon nanoparticles and interstellar extinction
To examine a recently proposed hypothesis that silicon nanoparticles are the
source of extended red emission (ERE) in the interstellar medium, we performed
a detailed modeling of the mean Galactic extinction in the presence of silicon
nanoparticles. For this goal we used the appropriate optical constants of
nanosized Si, essentially different from those of bulk Si due to quantum
confinement. It was found that a dust mixture of silicon nanoparticles, bare
graphite grains, silicate core-organic refractory mantle grains and three-layer
silicate-water ice-organic refractory grains works well in explaining the
extinction and, in addition, results in the acceptable fractions of UV/visible
photons absorbed by silicon nanoparticles: 0.071-0.081. Since these fractions
barely agree with the fraction of UV/visible photons needed to excite the
observed ERE, we conclude that the intrinsic photon conversion efficiency of
the photoluminescence by silicon nanoparticles must be near 100%, if they are
the source of the ERE.Comment: Latex2e, uses emulateapj.sty (included), multicol.sty, epsf.sty, 6
pages, 3 figures (8 Postscript files), accepted for publication in ApJ
Letters, complete Postscript file is also available at
http://physics.technion.ac.il/~zubko/eb.html#SNP
The Spectral Signature of Dust Scattering and Polarization in the Near IR to Far UV. I. Optical Depth and Geometry Effects
Spectropolarimetry from the near IR to the far UV of light scattered by dust
provides a valuable diagnostic of the dust composition, grain size distribution
and spatial distribution. To facilitate the use of this diagnostic, we present
detailed calculations of the intensity and polarization spectral signature of
light scattered by optically thin and optically thick dust in various
geometries. The polarized light radiative transfer calculations are carried out
using the adding-doubling method for a plane-parallel slab, and are extended to
an optically thick sphere by integrating over its surface. The calculations are
for the Mathis, Rumple & Nordsieck Galactic dust model, and cover the range
from 1 to 500 \AA. We find that the wavelength dependence of the
scattered light intensity provides a sensitive probe of the optical depth of
the scattering medium, while the polarization wavelength dependence provides a
probe of the grain scattering properties, which is practically independent of
optical depth. We provide a detailed set of predictions, including polarization
maps, which can be used to probe the properties of dust through imaging
spectropolarimetry in the near IR to far UV of various Galactic and
extragalactic objects. In a following paper we use the codes developed here to
provide predictions for the dependence of the intensity and polarization on
grain size distribution and composition.Comment: 29 pages + 21 figures, accepted for the Astrophysical Journal
Supplement February 2000 issue. Some revision, mostly in the introduction and
the conclusions, and a couple of correction
Water and Dust Emission from W Hydrae
We construct a self-consistent model for the wind around W Hya by solving the
coupled equations describing the hydrodynamics and dust radiative transfer
problems. The model matches simultaneously the observed continuum radiation and
wind velocity profile. The water line emission is calculated next using the
water abundance as the only free parameter, fitted from the ISO observations of
Neufeld et al. (1996) and Barlow et al. (1996). The gas temperature is
determined from a thermal balance calculation that includes water as one of its
main components. Our model successfully fits all the observed water lines,
resolving a major discrepancy between the modeling results of the two observing
teams. The mass loss rate is 2.3 x 10^{-6} M_solar yr^{-1}, the water abundance
is 1.0 x 10^{-4} and the ortho:para ratio is 1:1.3.Comment: 5 pages, 3 figures, uses aastex.cls and emulateapj5.sty, accepted by
ApJ Letter