1,432 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
"Colliding beam" enhancement mechanism of deuteron-deuteron fusion reactions in matter
We suggest a ``ping-pong'' mechanism of enhancement for fusion reactions
between a low energy external deuteron beam and the deuterons in a condensed
matter or molecular target. The mechanism is based on the possibility of
acceleration of a target deuteron by the Coulomb field of a projectile deuteron
with its subsequent rebound from a heavy atom in matter and the following
fusion of the two deuterons moving towards each other. This effectively
converts the fixed target process into a colliding beam reaction. In a simple
limiting case this reduces the negative penetrability exponent by a factor of
. We also discuss a contribution given by ``zero oscillations'' of a
bound target deuteron. The proposed mechanism is expected to be efficient in
compounds with target deuterons localized in the vicinity of heavy atoms.Comment: 4 page
- …