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  • 1
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    Airborne observations of the infrared emission bands (1989)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: Earlier airborne studies of the infrared bands between 5 and 8 microns have now been extended to a sample of southern sources selected from the IRAS Low Resolution Spectra (LRS) atlas. The correlation between the strongest bands at 6.2 and 7.7 microns is now based on a total sample of 40 sources and is very strong. A new emission band at 5.2 microns, previously predicted for polycyclic aromatic hydrocarbons (PAHs), is recognized in 27 sources; it too correlates with the dominant 7.7 micron band, showing that the 5.2 micron feature also belongs to the generic spectrum of PAH features at 3.3, 5.6, 6.2, 6.2, 7.7, 8.7, 11.3, and 12.7 microns. Sufficient sources are had now to define the relative strengths of most of these bands in three separate nebular environments: planetaries, H II regions, and reflection nebulae. Significant variations are detected in the generic spectra of PAHs in these different environments which are echoed by variations in the exact wavelength of the strong 7.7 micron peak. The earlier suggestion that, in planetaries, the fraction of total emission observed by IRAS that is carried by the PAH emissions is correlated with nebular gas-phase C/O ratio is supported by the addition of newly-observed southern planetaries, including the unusually carbon-rich (WC10) nebular nuclei. These (WC10) nuclei also exhibit a strong plateau of emission linking the 6.2 and 7.7 micron features.
    Keywords: ASTRONOMY
    Type: Interstellar Dust: Contributed Papers; p 93
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  • 2
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    Airborne observations of the infrared emission bands (1989)
    In:  CASI
    Details
    Publication Date: 2013-08-29
    Description: The data concerning low resolution airborne spectra from 5 to 8 microns available for a sample of 40 sources selected from the Infrared Astronomy Satellite low resolution spectral Atlas with polycyclic aromatic hydrocarbon (PAH) emission features, are discussed. A new emission band at 5.2 microns, previously predicted for PAHs, was found in 33 sources; it also correlates with the 7.7 microns band. This extends the spectrum of narrow observed PAH features to 3.3, 5.2, 5.6, 6.2, 6.9, 7.7, 8.7, 11.3, and 12.7 microns. From the data the relative strengths of most of these bands are defined in three separate nebular environments: planetaries, H II regions, and reflection nebulae. The differences in the PAHs spectra in those environments are analyzed.
    Keywords: ASTRONOMY
    Type: ESA, Infrared Spectroscopy in Astronomy; p 149-154
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  • 3
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    High rotational CO lines in post-AGB stars and PNe (1995)
    In:  Other Sources
    Details
    Publication Date: 2013-08-29
    Description: A significant fraction of a star's initial mass is lost while it is on the Asymptotic Giant Branch (AGB). Mass loss rates range from 10(exp -7) solar mass/yr for early AGB stars to a few 10(exp -4) solar mass/yr for stars at the tip of the AGB. Dust grains condense from the outflow as the gas expands and form a dust shell around the central star. A superwind (approximately 10(exp -4) to 10(exp -3) solar mass/yr) is thought to terminate the AGB phase. In the post-AGB phase, the star evolves to a higher effective temperature, the mass loss decreases (approximately 10(exp -8) solar mass/yr), but the wind velocity increases (approximately 1000 km/s). During this evolution, dust and gas are exposed to an increasingly harsher radiation field and when T(sub eff) reaches about 30,000 K, the nebula is ionized and becomes a planetary nebula (PN). Photons from the central star can create a photodissociation region (PDR) in the expanding superwind. Gas can be heated through the photoelectric effect working on small grains and polycyclic aromatic hydrocarbons (PAH's). This gas can cool via the atomic fine structure lines of O I (63 microns and 145 microns) and C II (158 microns), as well as the rotational lines of CO. In the post-AGB phase, the fast wind from the central star will interact with the material ejected during the AGB phase. The shock caused by this interaction will dissociate and heat the gas. This warm gas will cool through atomic fine structure lines of O I and the rotational lines of (newly formed) CO.
    Keywords: ASTRONOMY
    Type: Astronomical Society of the Pacific, Airborne Astronomy Symposium on the Galactic Ecosystem: From Gas to Stars to Dust, Volume 73; p 429-432
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  • 4
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    Infrared spectra of protostellar collapse (1995)
    In:  Other Sources
    Details
    Publication Date: 2013-08-29
    Description: Theoretical models of the formation of low mass stars by cloud collapse predict that OI(63 micrometers) and IR rotational lines of CO and H2O dominate the cooling in the freefalling region 10-1000 AU from the protostar. The freefalling gas supersonically hits the protoplanetary disk orbiting the protostar, forming an accretion shock with strong IR emission in rotational lines of H2O and OH, and OI(63 microns). The accretion shock spectra and line profiles depend on the mass flux through the shock and the typical distance r-bar at which the freefalling gas strikes the disk. The line widths are of order the Keplerian speed, or approx. 10(r-bar/10AU)(exp -0.5) km/s, for the accretion shock lines, and less for the lines from the infalling gas. Measurements of the IR line fluxes and profiles from the freefalling gas and the accretion shock diagnoses how a protostar and disk are formed and requires high sensitivity and high spectral and spatial resolving power. SOFIA will be the optimum observatory for many of these lines, although ISO will contribute and the KAO may make a few pioneering detections.
    Keywords: ASTRONOMY
    Type: Astronomical Society of the Pacific, Airborne Astronomy Symposium on the Galactic Ecosystem: From Gas to Stars to Dust, Volume 73; p 243-250
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  • 5
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    IR line emission from dense photodissociation regions (1989)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The results of the study on the molecular and fine structure line emission, from dense photodissociation regions, are discussed. The work is focused on the prediction of the line emission from CO and H2 molecules. It is found that, when the gas density is sufficiently high, self-shielding of the molecules can move the C(+)/CO and H/H2 transitions close to the surfaces of the molecular cloud where they can feel the full effect of heating by the ultraviolet radiation field. Collisional de-excitation of the H2 can move the lower levels towards low temperature emission producing an apparently shocked line ratio for two low-J levels, while the high-J levels retain a fluorescent value. Appreciable emission in high-J CO molecules originates in this warm molecular gas. Comparison with observation suggests that high density clumps are a common phenomena in photodissociation regions.
    Keywords: ASTRONOMY
    Type: ESA, Infrared Spectroscopy in Astronomy; p 141-147
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  • 6
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    The Unidentified Emission Features: a Study of the Orion Bar and Planetary Nebulae (1984)
    In:  CASI
    Details
    Publication Date: 2014-09-17
    Description: The unidentified emission features which are a group of broad emission bands found between 3.3 and 11.3 micro m in many objects which emit UV radiation and are associated with dust were studied. The features emit a substantial fraction of the energy in this wavelength range, and must therefore be an important constituent of the material around these objects. A two phase approach to the problem to better define the factors affecting the features was undertaken. The number of objects with good spectra between 3 and 13 micro m to look for correlations of the features with each other and with chemical and physical conditions were expanded and several positions in a single region, the Orion Bar, where the chemical composition was homogeneous, but the physical conditions varied are examined.
    Keywords: ASTRONOMY
    Type: Airborne Astron. Symp.; p 140-147
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  • 7
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    The Diffuse Interstellar Bands: Contributed papers (1994)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Drawing a coherent picture of the observational characteristics of the Diffuse Interstellar Bands (DIB's) and the physical and chemical properties of its proposed carriers was the focus of this NASA sponsored conference. Information relating to absoption spectra, diffuse radiation carriers, carbon compounds, stellar composition, and interstellar extinction involving T-Tauri stars, Reflection Nebulae, Red Giants, and accretion discs are discussed from those papers presented at the conference, which are included in this analytic.
    Keywords: ASTRONOMY
    Type: NASA-CP-10144 , A-94107 , NAS 1.55:10144 , May 16, 1994 - May 19, 1994; Boulder, CO; United States
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