279 research outputs found
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
Investigating the Near-Infrared Properties of Planetary Nebulae. I. Narrowband Images
We present the results of a near-infrared narrowband imaging survey of
planetary nebulae. Objects were selected in a way that complements similar
surveys done at visible and near-infrared wavelengths. No new detections of
molecular hydrogen emission were made. The H2 is frequently found to be
extended, except in young, visibly compact objects. Our results are consistent
with the already determined correlation of H2 emission with planetary nebula
morphological type. Filamentary and other kinds of structures are clearly
resolved in many nebulae.Comment: 21 pages text+tables and 38 figures, full preprint available at
http://www.cv.nrao.edu/html/library/nrao_preprints.html, report #9571 (4.4MB
gzipped file), or email [email protected]. Accepted ApJS, scheduled
Sept. 199
The Herschel-SPIRE instrument and its in-flight performance
The Spectral and Photometric Imaging REceiver (SPIRE), is the Herschel Space Observatory`s submillimetre camera and spectrometer. It contains a three-band imaging photometer operating at 250, 350 and 500 ÎŒm, and an imaging Fourier-transform spectrometer (FTS) which covers simultaneously its whole operating range of 194â671 ÎŒm (447â1550 GHz). The SPIRE detectors are arrays of feedhorn-coupled bolometers cooled to 0.3 K. The photometer has a field of view of 4ÂŽĂ 8ÂŽ, observed simultaneously in the three spectral bands. Its main operating mode is scan-mapping, whereby the field of view is scanned across the sky to achieve full spatial sampling and to cover large areas if desired. The spectrometer has an approximately circular field of view with a diameter of 2.6ÂŽ. The spectral resolution can be adjusted between 1.2 and 25 GHz by changing the stroke length of the FTS scan mirror. Its main operating mode involves a fixed telescope pointing with multiple scans of the FTS mirror to acquire spectral data. For extended source measurements, multiple position offsets are implemented by means of an internal beam steering mirror to achieve the desired spatial sampling and by rastering of the telescope pointing to map areas larger than the field of view. The SPIRE instrument consists of a cold focal plane unit located inside the Herschel cryostat and warm electronics units, located on the spacecraft Service Module, for instrument control and data handling. Science data are transmitted to Earth with no on-board data compression, and processed by automatic pipelines to produce calibrated science products. The in-flight performance of the instrument matches or exceeds predictions based on pre-launch testing and modelling: the photometer sensitivity is comparable to or slightly better than estimated pre-launch, and the spectrometer sensitivity is also better by a factor of 1.5â2
Is the Cepheus E Outflow driven by a Class 0 Protostar?
New early release observations of the Cepheus E outflow and its embedded
source, obtained with the Spitzer Space Telescope, are presented. We show the
driving source is detected in all 4 IRAC bands, which suggests that traditional
Class 0 classification, although essentially correct, needs to accommodate the
new high sensitivity infrared arrays and their ability to detected deeply
embedded sources. The IRAC, MIPS 24 and 70 microns new photometric points are
consistent with a spectral energy distribution dominated by a cold, dense
envelope surrounding the protostar. The Cep E outflow, unlike its more famous
cousin the HH 46/47 outflow, displays a very similar morphology in the near and
mid-infrared wavelengths, and is detected at 24 microns. The interface between
the dense molecular gas (where Cep E lies) and less dense interstellar medium,
is well traced by the emission at 8 and 24 microns, and is one of the most
exotic features of the new IRAC and MIPS images. IRS observations of the North
lobe of the flow confirm that most of the emission is due to the excitation of
pure H2 rotational transitions arising from a relatively cold (Tex~700 K) and
dense (N{H}~9.6E20 cm-2 molecular gas.Comment: 14 pages (pre-print format), including 6 figures. Published in ApJ
Special Spitzer Issue (2004
Infrared Observations of the Helix Planetary Nebula
We have mapped the Helix (NGC 7293) planetary nebula (PN) with the IRAC instrument on the Spitzer Space Telescope. The Helix is one of the closest bright PNs and therefore provides an opportunity to resolve the small-scale structure in the nebula. The emission from this PN in the 5.8 and 8 Όm IRAC bands is dominated by the pure rotational lines of molecular hydrogen, with a smaller contribution from forbidden line emission such as [Ar III] in the ionized region. The IRAC images resolve the "cometary knots," which have been previously studied in this PN. The "tails" of the knots and the radial rays extending into the outer regions of the PN are seen in emission in the IRAC bands. IRS spectra on the main ring and the emission in the IRAC bands are consistent with shock-excited H_2 models, with a small (~10%) component from photodissociation regions. In the northeast arc, the H_2 emission is located in a shell outside the Hα emission
- âŠ