35 research outputs found
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
Infrared Period-Luminosity Relations of Evolved Variable Stars in the Large Magellanic Cloud
We combine variability information from the MAssive Compact Halo Objects
(MACHO) survey of the Large Magellanic Cloud (LMC) with infrared photometry
from the Spitzer Space Telescope Surveying the Agents of a Galaxy's Evolution
(SAGE) survey to create a dataset of ~30 000 variable red sources. We
photometrically classify these sources as being on the first ascent of the Red
Giant Branch (RGB), or as being in one of three stages along the Asymptotic
Giant Branch (AGB): oxygen-rich, carbon-rich, or highly reddened with
indeterminate chemistry ("extreme" AGB candidates). We present linear
period-luminosity relationships for these sources using 8 separate infrared
bands (J, H, K, 3.6, 4.5, 5.8, 8.0, and 24 micron) as proxies for the
luminosity. We find that the wavelength dependence of the slope of the
period-luminosity relationship is different for different photometrically
determined classes of AGB stars. Stars photometrically classified as O-rich
show the least variation of slope with wavelength, while dust enshrouded
extreme AGB stars show a pronounced trend toward steeper slopes with increasing
wavelength. We find that O-rich AGB stars pulsating in the fundamental mode
obey a period-magnitude relation with a slope of -3.41 +/- 0.04 when magnitude
is measured in the 3.6 micron band, in contrast to C-rich AGB stars, which obey
a relation of slope -3.77 +/- 0.05
The Red Rectangle: Its Shaping Mechanism and its Source of Ultraviolet Photons
The proto-planetary Red Rectangle nebula is powered by HD 44179, a
spectroscopic binary (P = 318 d), in which a luminous post-AGB component is the
primary source of both luminosity and current mass loss. Here, we present the
results of a seven-year, eight-orbit spectroscopic monitoring program of HD
44179, designed to uncover new information about the source of the
Lyman/far-ultraviolet continuum in the system as well as the driving mechanism
for the bipolar outflow producing the current nebula. Our observations of the
H-alpha line profile around the orbital phase of superior conjunction reveal
the secondary component to be the origin of the fast (max. v~560^{-1}\sun_{max} \ge 17,0002 -
5\times10^{-5}\sun^{-1}\sun$, about 5% of the
luminosity of the entire system. (abridged)Comment: Accepted for publication in Ap
A COMPLETE SPECTROSCOPIC MAP AND NARROW-BAND IMAGING OF SMALL PAHS IN THE RED RECTANGLE NEBULA
Author Institution: Ritter Astrophysical Research Center, Univeristy of Toledo, Toledo, OH 43606; University of Chicago, Chicago, IL 60637; NASA Goddard Space Flight Center, Greenbelt, MD 20771; McDonald Observatory, University of Texas at Austin, Austin, TX 78712Electronic flurescence spectra (peak 375 nm) in reflection nebulae have helped to identify the largest molecules that have been detected so far in the interstellar medium: 3-4 ringed polycyclic aromatic hydrocarbons (PAHs). This detection of blue luminescence (BL) by small, neutral PAHs was first made in the peculiar, proto-planetary nebula, the Red Rectangle. This first detection and subsequent observations in other reflection nebulae reveal spatial variations in the BL spectrum indicating a change in the size distribution/ionisation state of the emitters. Data from an ongoing, complete spectroscopic survey and narrow-band imaging of the Red Rectangle will be presented. This study sheds light on the spatial distribution, ionization state and the size distributions of the small PAHs in this nebula
Optical Emission Band Morphologies of the Red Rectangle
We present narrow-band images of the Red Rectangle (RR) nebula which reveal
the distinct morphologies of this intriguing nebula in different optical
emission bands. The morphology of the RR nebula in blue luminescence (BL) and
extended red emission (ERE) are almost mutually exclusive. We also present the
optical detection of the circum-binary disk of the RR in the light of the BL.
The total intensities from the two optical band emissions (BL and ERE) when
summed over the nebula are of comparable magnitude. Their spatial distributions
with respect to the embedded illumination sources lead us to suggest that they
may be attributed to different ionization stages of the same family of
carriers.Comment: Accepted to Ap
On the Origins of the High-Latitude H-alpha Background
The diffuse high-latitude H-alpha background is widely believed to be
predominantly the result of in-situ recombination of ionized hydrogen in the
warm interstellar medium of the Galaxy. Instead, we show that both a
substantial fraction of the diffuse high-latitude H-alpha intensity in regions
dominated by Galactic cirrus dust and much of the variance in the high-latitude
H-alpha background are the result of scattering by interstellar dust of H-alpha
photons originating elsewhere in the Galaxy. We provide an empirical relation,
which relates the expected scattered H-alpha intensity to the IRAS 100um
diffuse background intensity, applicable to about 81% of the entire sky. The
assumption commonly made in reductions of CMB observations, namely that the
observed all-sky map of diffuse H-alpha light is a suitable template for
Galactic free-free foreground emission, is found to be in need of
reexamination.Comment: 26 pages, 5 figures, Accepted for publication in Ap