88 research outputs found
Dust Scattering In Turbulent Media: Correlation Between The Scattered Light and Dust Column Density
Radiative transfer models in a spherical, turbulent interstellar medium (ISM)
in which the photon source is situated at the center are calculated to
investigate the correlation between the scattered light and the dust column
density. The medium is modeled using fractional Brownian motion structures that
are appropriate for turbulent ISM. The correlation plot between the scattered
light and optical depth shows substantial scatter and deviation from simple
proportionality. It was also found that the overall density contrast is
smoothed out in scattered light. In other words, there is an enhancement of the
dust-scattered flux in low-density regions, while the scattered flux is
suppressed in high-density regions. The correlation becomes less significant as
the scattering becomes closer to be isotropic and the medium becomes more
turbulent. Therefore, the scattered light observed in near-infrared wavelengths
would show much weaker correlation than the observations in optical and
ultraviolet wavelengths. We also find that the correlation plot between
scattered lights at two different wavelengths shows a tighter correlation than
that of the scattered light versus the optical depth.Comment: 6 pages, 5 figure, accepted for publication in the ApJ Letter
The size distribution of interstellar grains
Three major areas involving interstellar grains were investigated. First, studies were performed of scattering in reflection nebulae with the goal of deriving scattering characteristics of dust grains such as the albedo and the phase function asymmetry throughout the visible and the ultraviolet. Secondly, studies were performed of the wavelength dependence of interstellar extinction designed to demonstrate the wide range of grain size distributions naturally occurring in individual clouds in different parts of the galaxy. And thirdly, studies were also performed of the ultraviolet powered emission of dust grains in the 0.5 to 1.0 micron wavelength range in reflection nebulae. Findings considered of major importance are highlighted
Discovery of Blue Luminescence in the Red Rectangle: Possible Fluorescence from Neutral Polycyclic Aromatic Hydrocarbon Molecules?
Here we report our discovery of a band of blue luminescence (BL) in the Red
Rectangle (RR) nebula. This enigmatic proto-planetary nebula is also one of the
brightest known sources of extended red emission as well as of unidentified
infra-red (UIR) band emissions. The spectrum of this newly discovered BL is
most likely fluorescence from small neutral polycyclic aromatic hydrocarbon
(PAH) molecules. PAH molecules are thought to be widely present in many
interstellar and circumstellar environments in our galaxy as well as in other
galaxies, and are considered likely carriers of the UIR-band emission. However,
no specific PAH molecule has yet been identified in a source outside the solar
system, as the set of mid-infra-red emission features attributed to these
molecules between the wavelengths of 3.3 micron and 16.4 micron is largely
insensitive to molecular sizes. In contrast, near-UV/blue fluorescence of PAHs
is more specific as to size, structure, and charge state of a PAH molecule. If
the carriers of this near-UV/blue fluorescence are PAHs, they are most likely
neutral PAH molecules consisting of 3-4 aromatic rings such as anthracene
(C14H10) and pyrene (C16H10). These small PAHs would then be the largest
molecules specifically identified in the interstellar medium.Comment: 4 pages, 4 figures, Accepted for publication in ApJL (LaTeX, uses
emulateapj.sty
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