1,203 research outputs found
Circumstellar dust
The presence of dust in the general interstellar medium is inferred from the extinction, polarization, and scattering of starlight; the presence of dark nebulae; interstellar depletions; the observed infrared emission around certain stars and various types of interstellar clouds. Interstellar grains are subject to various destruction mechanisms that reduce their size or even completely destroy them. A continuous source of newly formed dust must therefore be present for dust to exist in the various phases of the interstellar medium (ISM). The working group has the following goals: (1) review the evidences for the formation of dust in the various sources; (2) examine the clues to the nature and composition of the dust; (3) review the status of grain formation theories; (4) examine any evidence for the processing of the dust prior to its injection into the interstellar medium; and (5) estimate the relative contribution of the various sources to the interstellar dust population
On the detectability of infrared echo arcs around supernova 1987A
The ring-like interstellar visual echoes of radii 33 and 54 arcsec detected around SN 1987A should coincide with infrared echoes (thermal reradiation) from dust at T approximately equal to 15 to 30 K. Whether these infrared echoes are detectable at present is considered. They will be brightest at approximately 100 microns, the range of the Texas infrared photometer. Detectability depends on the ratio zeta congruent to tan(sub a)/tan(sub s)P(theta), where tan(sub a) and tan(sub s) are the visual absorption and scattering optical thicknesses of the echo layer, and P is the phase function function for small-angle scattering (theta approximately equal to 2 to 4 degrees). Zeta approximately greater than 1 is needed for a detectable signal (approximately 0.3 Jy), but zeta cannot be much less than 1; otherwise the visual echoes could not be as bright as they are. Typical dust mixtures of Mathis-Rumpl-Nordsieck type have zeta much less than 1. Zeta remains small even if a population of very small grains with power-law index as steep as approximately 5.5 is added. A population with even more small grains and/or fewer large grains could have a zeta similar to 1 and be detectable at present, but this seems unlikely. The echoes will move, but should remain accessible for many years and should be detected eventually
Infrared studies of supernova remnants with the IRAS
A comparative study of the infrared and X-ray fluxes and morphologies of supernova remnants (SNR) can yield valuable information on their evolution and on their interaction with the smbient interstellar medium (ISM)
Constraints to Energy Spectra of Blazars based on Recent EBL Limits from Galaxy Counts
We combine the recent estimate of the contribution of galaxies to the 3.6
micron intensity of the extragalactic background light (EBL) with optical and
near-infrared (IR) galaxy counts to set new limits on intrinsic spectra of some
of the most distant TeV blazars 1ES 0229+200, 1ES 1218+30.4, and 1ES 1101-232,
located at redshifts 0.1396, 0.182, and 0.186, respectively. The new lower
limit on the 3.6 micron EBL intensity is significantly higher than the previous
one set by the cumulative emission from resolved Spitzer galaxies. Correcting
for attenuation by the revised EBL, we show that the differential spectral
index of the intrinsic spectrum of the three blazars is 1.28 +- 0.20 or harder.
These results present blazar emission models with the challenge of producing
extremely hard intrinsic spectra in the sub-TeV to multi-TeV regime. These
results also question the reliability of recently derived upper limits on the
near-IR EBL intensity that are solely based on the assumption that intrinsic
blazar spectra should not be harder than 1.5.Comment: 13 pages, 2 figures, submitted to the Astrophysical Journa
The large scale gas and dust distribution in the galaxy: Implications for star formation
Infrared Astronomy Observations are presented for the diffuse infrared (IR) emissions from the galactic plane at wavelengths of 60 and 100 microns and the total far infrared intensity and its longitudinal variations in the disk were derived. Using available CO, 5 GHz radio-continuum, and HI data, the IR luminosity per hydrogen mass and the ingrared excess (IRE) ratio in the Galaxy were derived. The longitudinal profiles of the 60 and 100 micron emission were linearly decomposed into three components that are associated with molecular (H2), neutral (HI), and ionized (HII) phases in the interstellar medium (ISM), and the relevant dust properties were derived in each phase. Implications of the findings for various models of the diffuse IR emisison and for star formation in the galactic disk are discussed
A Tentative Detection of the Cosmic Infrared Background at 3.5 microns from COBE/DIRBE Observations
Foreground emission and scattered light from interplanetary dust (IPD)
particles and emission from Galactic stellar sources are the greatest obstacles
for determining the cosmic infrared background (CIB) from diffuse sky
measurements in the ~ 1 to 5 micron range. We use ground-based observational
limits on the K-band intensity of the CIB in conjunction with skymaps obtained
by the Diffuse Infrared Background Experiment (DIRBE) on the COBE satellite to
reexamine the limits on the CIB at 1.25, 3.5, and 4.9 microns. Adopting a CIB
intensity of 7.4 nW m-2 sr-1 at 2.2 microns, and using the 2.2 micron DIRBE
skymap from which the emission from IPD cloud has been subtracted, we create a
spatial template of the Galactic stellar contribution to the diffuse infrared
sky. This template is then used to subtract the contribution of the diffuse
Galactic stellar emission from the IPD-emission-subtracted DIRBE skymaps. The
DIRBE 100 micron data are used to estimate the small contribution of emission
from interstellar dust at 3.5 and 4.9 microns. Our method significantly reduces
the errors associated with the subtraction of Galactic starlight, leaving only
the IPD emission component as the primary obstacle for the detection of the CIB
at these wavelengths. This analysis leads to a tentative detection of the CIB
at 3.5 microns. The cosmological implications of these results are discussed in
the paper.Comment: 8 pages, AASTeX, 2 embedded EPS figures. Accepted for publication in
ApJ Letter
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