161 research outputs found
Infrared Imaging of Planetary Nebulae from the Ground Up
New ground-based telescopes and instruments, the return of the NICMOS
instrument on the Hubble Space Telescope (HST), and the recent launch of the
Spitzer Space Telescope have provided new tools that are being utilized in the
study of planetary nebulae. Multiwavelength, high spatial resolution
ground-based and HST imaging have been used to probe the inner regions of young
PNe to determine their structure and evaluate formation mechanisms.
Spitzer/IRAC and MIPS have been used to image more evolved PNe to determine the
spatial distribution of molecular hydrogen, ionized gas, and dust in the
nebulae and halos.Comment: 8 pages, 3 figures, invited review given at IAU Symp. 234, to appear
in "Planetary Nebulae in Our Galaxy and Beyond", eds. M. J. Barlow & R. H.
Mende
The Near-Infrared Structure and Spectra of the Bipolar Nebulae M 2--9 and Afgl 2688: The Role of UV-Pumping and Shocks in Molecular Hydrogen Excitation
High-resolution near-infrared images and moderate resolution spectra were
obtained of the bipolar nebulae M~2--9 and AFGL 2688. The ability to spatially
and spectrally resolve the various components of the nebulae has proved to be
important in determining their physical structure and characteristics. In
M~2--9, the lobes are found to have a double-shell structure. Analysis of \h2\
line ratios indicates that the \h2\ emission is radiatively excited. A
well-resolved photodissociation region is observed in the lobes. The spectrum
of the central source is dominated by H recombination lines and a strong
continuum rising towards longer wavelengths consistent with a K
blackbody. In AFGL 2688, the emission from the bright lobes is mainly continuum
reflected from the central star. Several molecular features from C and CN
are present. In the extreme end of the N lobe and in the E equatorial region,
the emission is dominated by lines of \h2 in the 2--2.5 \microns region. The
observed \h2 line ratios indicate that the emission is collisionally excited,
with an excitation temperature K.Comment: 28 pages, 13 figures,uuencoded compressed postscript, printed version
available by request from [email protected], IfA-94/3
A Semi-Automated Computational Approach for Infrared Dark Cloud Localization: A Catalog of Infrared Dark Clouds
The field of computer vision has greatly matured in the past decade, and many
of the methods and techniques can be useful for astronomical applications. One
example is in searching large imaging surveys for objects of interest,
especially when it is difficult to specify the characteristics of the objects
being searched for. We have developed a method using contour finding and
convolution neural networks (CNNs) to search for Infrared Dark Clouds (IRDCs)
in the Spitzer Galactic plane survey data. IRDCs can vary in size, shape,
orientation, and optical depth, and are often located near regions with complex
emission from molecular clouds and star formation, which can make the IRDCs
difficult to reliably identify. False positives can occur in regions where
emission is absent, rather than from a foreground IRDC. The contour finding
algorithm we implemented found most closed figures in the mosaic and we
developed rules to filter out some of the false positive before allowing the
CNNs to analyze them. The method was applied to the Spitzer data in the
Galactic plane surveys, and we have constructed a catalog of IRDCs which
includes additional parts of the Galactic plane that were not included in
earlier surveys.Comment: 17 pages, 18 figures, one machine-readable table. Accepted for
publication in the PAS
The nebulae around LBVs: a multiwavelength approach
We present first results of our study of a sample of Galactic LBV, aimed to
contribute to a better understanding of the LBV phenomenon, by recovering the
mass-loss history of the central object from the analysis of its associated
nebula. Mass-loss properties have been derived by a synergistic use of
different techniques, at different wavelengths, to obtain high-resolution,
multi-wavelength maps, tracing the different emitting components coexisting in
the stellar ejecta: the ionized/neutral gas and the dust. Evidence for
asymmetric mass-loss and observational evidence of possible mutual interaction
between gas and dust components have been observed by the comparison of mid-IR
(Spitzer/IRAC, VLT/VISIR) and radio (VLA) images of the nebulae, while
important information on the gas and dust composition have been derived from
Spitzer/IRS spectra.Comment: 5 pages, 4 figures. To appear in proceedings of 39th Liege
International Astrophysical Colloquium: The multi-wavelength view of Hot,
Massive Star
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