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  • 1
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    Infrared emission line studies of the structure and excitation of H II regions (1982)
    In:  Other Sources
    Details
    Publication Date: 2011-08-18
    Description: Maps of five H II regions in one or more of the infrared fine-structure lines of Ne II (12.8 microns), Ar III (9.0 microns), and S IV (10.5 microns) have been obtained with angular resolutions ranging from 4 to 7 arcsec. The observations are used to discuss the morphology and excitation of these nebulae. Considerable diversity is found in the structures of the nebulae, probably resulting from differences in their ages and the circumstances of their formation. In all cases, more ionizing luminosity than would be provided by a single dominant ionizing star appears to be required, although uncertainties in the model nebulae make this conclusion uncertain.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 255
    Format: text
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  • 2
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    Infrared line and continuum views of G333.6-0.2 (1981)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: A 1-micron CCD picture and maps of the Ne II and Ar III fine-structure lines have been obtained in a region roughly one arcmin in size centered on the core of the compact H II region G333.6 - 0.2. The two emission-line maps show nearly identical intensity distributions, although much different fluxes. The maps are similar to the 1-micron picture smoothed to their angular resolutions. The infrared line of S IV also was detected and appears to have a spatial intensity distribution similar to that of the other fine-structure lines. The 1-micron picture reveals a small number of objects of nearly stellar appearance in the core, suggesting that G333.6 - 0.2 is powered by a compact cluster of sources. Stellar continuum radiation probably is responsible in part for the low equivalent width of the B-gamma line in the core.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 247
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  • 3
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    High spectral and spatial resolution observations of the 12.28 micron emission from H2 in the Orion Molecular Cloud (1982)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: The pure rotational S(2) line of H2 at 12.28 microns was sought in 44 positions in the Orion Molecular Cloud with 6-arcsec beams and 35 km/s spectral resolution; and it was detected in 27 positions. The lines are approximately symmetric and have full widths at half-maximum ranging from 100 km/s down to the resolution limit. The distribution of intensities and line shapes is largely consistent with that observed in the 2-micron hydrogen transitions; however, unexpectedly complex line profiles and point-to-point variations in line shapes appear, particularly in the region near IRc9.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 253
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  • 4
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    The abundances of neon, sulfur, and argon in planetary nebulae (1981)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: New infrared observations of Ne II, Ar III, and S IV are used in optical observations of other ionization states of the considered elements to evaluate the abundances of neon, argon, and sulfur in 18 planetary nebulae. Attention is also given to one or more of the infrared lines in 18 other nebulae. It is pointed out that S IV was detected in approximately 90% of the observed objects, while Ar III was found in about 80%, and Ne II in roughly one-third. It is noted that optical observations typically include only a limited region of the nebula, while the infrared measurements frequently involve integration over the entire nebular image.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal; vol. 249
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  • 5
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    The structure of high-velocity gas in Orion and the possible role of IRc9 (1984)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: The spatial and velocity distribution of shocked gas in the Orion molecular cloud has been studied in detail through observations of near-infrared and middle-infrared H2 lines. It is argued that the observed structure requires either an asymmetric outflow or an inhomogeneous ambient molecular cloud, and that the second explanation appears the more likely. It is suggested that mild activity by IRc9, such as a T Tauri type wind or FU Orionis type flare, would be consistent with its apparent nature and could have caused the necessary density structure in the cloud.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 281; 205-208
    Format: text
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  • 6
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    The distribution of shocked gas in the bipolar nebulae CRL 2688 and CRL 618 (1984)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Maps of the H2 emission from the bipolar nebulae CRL 2688 and CRL 618 are presented, along with a map of the 2.1-micron continuum emission from CRL 2688. The H2 emission is seen in the direction of the lobes of each nebula and not in between the lobes. From the distribution of the H2 and continuum emission, it is argued that the H2 is excited in shock waves produced in the lobes of the visible nebulae by fast winds from the central stars which overtake slower moving material lost in a slow wind during the red-giant phase of each object. These shocks may be similar to those seen in Herbig-Haro objects. The mass-loss rates for the fast winds in each object are estimated from the H2 data, and a brief discussion is given of the origin of these winds.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 280; 648-652
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  • 7
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    The spatial distribution of shocked gas in the Orion nebula (1983)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Observations of the spatial distribution of extinction and excitation temperature toward the molecular hydrogen emission in the Orion molecular cloud OMC-1 are presented. Most, although not all, of the observed structure in the near-infrared line intensities results from variations in the column density of vibrationally excited H2 and is not due to variable extinction or temperature. The extinction toward the center of the emission region is between 1 and 2 mag at 4712/cm, the frequency of the v = 1-0 S(1) line, but increases toward the edges. The lack of emission from the eastern part of the nebula may result from increased extinction in that direction. Variations in the extinction temperature are less than the observational uncertainties of + or - 200 K at all but one position observed. Therefore, the excitation temperature of the hydrogen molecules is probably not a strong function of either the shock velocity or the density of the gas. Observations of the v = 3-2 S(3) line in the direction of strongest emission indicate the presence of gas temperatures about 2700 K and place constraints on the column density of gas which is at higher temperature.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 271; Aug. 1
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  • 8
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    Observations of infrared hydrogen recombination line emission from external galaxies (1984)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Observations of infrared hydrogen recombination line emission are presented for several positions within the galaxies NGC 1068, NGC 1097, NGC 2903, and NGC 4151. Emission is seen from the arms and nuclei of these spiral galaxies. The luminosity from the most recent burst of star formation is deduced and compared to the infrared luminosity which accounts for the bulk of the total energy. Young stars (primarily O and B stars) provide most of the luminosity in the arms and nuclei of the normal galaxies NGC 1097 and NGC 2903. The infrared luminosities of the nuclei in the Seyfert galaxies NGC 1068 and NGC 4151 exceed those provided by young stars by factors of approximately 10.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 279; 563-566
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  • 9
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    Star formation in the nucleus of NGC 253 (1984)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: The B-alpha and B-gamma lines of atomic hydrogen have been observed at eight positions near the nucleus of NGC 253 with 6 arcsec spatial resolution. Most if not all of the bolometric luminosity of the central 200 pc of this galaxy is probably produced by O and B stars which have recently formed. The spatial distribution of the line fluxes is similar to that of the 10 microns flux, supporting the hypothesis that the 10 microns radiation is powered by the newly formed stars. The extinction to the ionized gas varies over small distances in this region, explaining the discrepancies between extinction and Lyman continuum luminosity derived separately from visual and infrared line observations.
    Keywords: ASTROPHYSICS
    Type: Royal Astronomical Society, Monthly Notices (ISSN 0035-8711); 207; 671-677
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