摘要:

I describe the astronomical regions in which chemistry is known to occur, and list the types of molecules that have been positively identified. Some of the successes and failures of chemistries that have been proposed to give rise to these molecular species are reviewed. The evidence which supports the view that processes on and in interstellar dust contribute to the overall chemistry are highlighted. Present ideas concerning the nature of interstellar dust and its response to the changing conditions in the interstellar medium are presented, so that the role of dust in interstellar chemistry can be considered. Current problems and directions of future work are indicated. © 1994American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.46564

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

We have used the Canada‐France‐Hawaii Telescope to obtain an image of vibrationally excited H2at 2.121 &mgr;m in NGC2023, at a spatial resolution of ∼1‘. The image has structures in the form of filaments of bright emission, showing clear spatial correlations and anti‐correlations with extended red emission (ERE). Our results have implications for the mechanism of the formation of ERE. Interpreting our observations in terms of the standard UV mechanism for the excitation of H2, we deduce that the surface of the emitting zone is characterized by undularions, whose morphology traces that of the emission. © 1994American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.46608

出版商:AIP    

年代:1994

数据来源: AIP

ISSN:0094-243X    

DOI:10.1063/1.46616

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

We have studied a sample of seven dark clouds (Bok globules) and eight Hergib Ae/Be stars in the J=1 → 0 transition of HCO+, H13CO+, HCN, and H13CN. The most abundant isotopomers were found in almost all the sources (detection rate 70–90%).From the derived physical parameters and column densities it seems that a quite similar scenario applies for the dark clouds and the gas around the Herbig stars. These similarities, together with the already known features from literature, suggest that the presently studied globules are likely to be sites of low‐mass star formation. © 1994American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.46563

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

Sensitive searches for13CO and C18OJ=1 → 0 emission are presented for a sample of translucent molecular clouds previously studied by optical absorption lines towards background stars. C18O has been detected in only 5 clouds, most of which have extinctions well in excess of 2 mag. The inferred13CO/C18O abundance ratios range from 7–25, and the lower limits from ≳13 to ≳35. These values are as much as five times larger than the overall interstellar ([13C]⋅[16O])/([12C]⋅[18O]) ratio, suggesting that isotope–selective photodissociation plays a role in at least some of the clouds. Searches for other molecules at millimeter wavelengths have been made for a few of the best characterized clouds. Surprisingly, no emission was detected from the C2H or C3H2molecules, even though the abundances of diatomic C2and CH are quite large. On the other hand, the abundance of HCO+appears comparable to that found in denser clouds, and abundance of HCN may be up to an order of magnitude larger than the prediction of models in two clouds. © 1994American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.46571

出版商:AIP    

年代:1994

数据来源: AIP

ISSN:0094-243X    

DOI:10.1063/1.46578

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

We are presented a quantitative analysis of the emission bands at 7.7 and 11.3 &mgr;m in IRAS/LRS spectra of 113 sources (H II regions, reflection nebulae, planetary nebulae and galaxies). Relations of the intensities of the emission bands with physical conditions such as the excitation, and the relative contribution of emission bands and continuum around 10 &Mgr;M to the mid‐infrared and far‐infrared fluxes are presented and analyzed. A strong linear correlation is found between the (7.7+8.6) &mgr;m and the 11.3 &mgr;m band luminosities. The correlation confirms, on a large number of sources, that the carriers of these emission bands belong to the same family, most likely aromatic molecular. The ratio of 7.7 and 11.3 &mgr;m intensities is equal to 8.3 (±3). The average contribution of these features to the mid‐infrared luminsotiy is 50%, and the importance of the underlying continuum is stressed in planetary nebulae, since this contribution is weaker (about 30%). The contribution of the near‐infrared emission bands to the total infrared luminosity is a few precent, implying that one to five percent of the cosmic carbon is located in aromatic molecules. From simple energetic considerations, it is show that the excitation of the 7.7 and 11.3 &mgr;m emission bands is dominated by ultraviolet photons in the range 91 to 365 nm. © 1994American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.46584

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

We present the observation of the 6.2 &mgr;m emission of the inner galactic disk obtained with the AROME balloon‐borne experiment. The galactic coordinates of the covered region are −5°≤1≤35° and ‖ b‖≤6°, with an angular resolution of 0.7°. The measurements reveal the existence of an emission feature at 6.2 &mgr;m all over this region. The averaged 6.2 &mgr;m surface brightness (‖ b ‖≤1°, 8°≤1≤35°) is &lgr;I&lgr;=(1.2±0.3) 10−5Wm−2sr−1, with a continuum &lgr; I&lgr;=(5.9±1.2) 10−6Wm−2sr−1and a feature’s intensity &Dgr;&lgr; I&lgr;=(6.1±1.3) 10−7Wm−2sr−1. We can compare this value to the 3.3 &mgr;m emission observed with AROME (Giardet al.19881) and to the 12 &mgr;m (IRAS) surface brightness: the ratios are respectively &Dgr;&lgr; I&lgr;(6.2/3.3)=9±2 (extinction corrected) and &Dgr;&lgr; I&lgr; 6.2/&lgr; I&lgr;12=0.09±0.02; these color ratios are similar to those obtained on UV excited nebulae, despite very different radiation field intensities. This supports the idea of a common origin for the near infrared radiation from excited nebulae and the diffuse interstellar medium: emission of transiently heated very small grains or large molecules like PAHs, as it was originally proposed by Pugetet al.(19852). © 1994American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.46648

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

We present new medium resolution spectroscopy (&lgr;/&Dgr;&lgr;≊1000) between 3.37 and 3.66 &mgr;m towards the deeply embedded source GL 2136. Besides an absorption feature at 3.535 &mgr;m due to solid CH3OH which was ealier observed towards other embedded sources, a new feature is apparent at 3.477 &mgr;m. From comparison with laboratory data of low temperature ices, we tentatively assign this feature to solid formaldehyde. Our dats combined with earlier observations of CO and H2O indicate towards GL 2136 an ice composition of H2O : CH3OH : H2CO : CO =100 : 3.6 : 2.5 : 3.0. © 1994The American Geophysical

ISSN:0094-243X    

DOI:10.1063/1.46631

出版商:AIP    

年代:1994

数据来源: AIP

摘要:

Maps of diffuse regions show that not only are IRAS color ratios higher than expected from standard grain models, but also vary with total emission in a way that is difficult to explain. It is shown here that in fact the gross general features of this emission can be attributed to the degree of processing of carbonaceous grain mantles, symptomatic of the dynamical nature of such regions. © 1994American Institute of Physics

ISSN:0094-243X    

DOI:10.1063/1.46640

出版商:AIP    

年代:1994

数据来源: AIP