Molecular clouds spectra

Figure Bl.4.3. (a) A schematic illustration of the THz emission spectrum of a dense molecular cloud core at 30 K and the atmospheric transmission from ground and airborne altitudes (adapted, with pennission, from [17]). (b) The results of 345 GHz molecular line surveys of tlu-ee cores in the W3 molecular cloud the graphics at left depict tire evolutionary state of the dense cores inferred from the molecular line data [21],...

Fig. 3.13 151 GHz Spectrum (excerpt) from the nucleus of the molecular cloud G 327.3-0.6 in the southern sky. The molecular species identified are shown. Peaks which are not labelled are not yet clearly identified. (The numbers used to label the molecular cloud, G 327.3-0.6, are galactic coordinates). With personal permission of Prof. Hjalmarsson, Chalmers University of Technology, Goteborg, Sweden, from the Proceedings of the First European Workshop on Exo/Astrobiology, Frascati, 21-23 May 2001, ESA SP-496...

Further increases in sensitivity and resolution of observational spectrometers will lead us to the detection of Hj in interstellar space. If detected, the spectrum will give crucial information on the working of the ion-neutral reaction scheme for the chemical evolution of molecular clouds. 

By comparing die observed spectra with spectra measured in die laboratory, one can determine the crystallinity of icy grains [3]. For Elias 16 (a molecular cloud), the observed feature around 3 pm fits die spectrum of amorphous ice at... 

The picture of a gas-phase chemistry in the dense molecular clouds, initiated by cosmic ray ionization of H2 and He, has been greatly strengthened by the direct observation of the very early reactant 11 (Oka, 1992). The identification and determination of the spectrum of H have been a great triumph of laboratory studies (Oka, 1980). This ion is now observed in absorption in many sources by means of its vibrational spectrum (McCall et al., 1998), as well as in planetary atmospheres in emission (Oka, 1992). Its abundance allows critical exploration of ionizing fluxes, primarily cosmic rays, and further provides an exceptional sight into dense molecular clouds. 

K. For the BN object (a protostar), the spectrum is optimized for a mixture of ices at representative temperatures of 23 K (amorphous), 77 K (amorphous), and 150K (crystalline ice). This shows that the BN have various temperatures ranging from circumstellar to molecular cloud temperatures, depending on the distance from the central protostar. 

GHz. This line was measured towards the cold, dark cloud L673 (2) and the molecular cloud M17-NW. The nitrogen nucleus has a spin of 1(N) = 1 / is the quantum number defining nuclear spin. An important spectroscopic effect of nuclear spin is quadrupole hyperfme structure. Consequently, the spectrum of the J= 1 -> 0 transition is split into three hyperfine components, indicated by the quantum number F F = J + I), which provides a spectral fingerprint for HCN. In order of increasing frequency, these transitions are labeled F= ->, F= —> 2, and F = 1 0. The intrinsic, or fundamental, intensity of the three... 

Using the spectroscopic parameters for HCO and HCCCN, the students then observed the 7 = 1 0 transition of HCO and the J = 9 -> 8 transition of HCCCN in the Orion molecular cloud. The spectrum recorded for HCO is displayed in the top panel of Figure 6. These results demonstrated to the students that unusual species present in interstellar gas can be made under extreme conditions for fractions of seconds on Earth. 

Figure Bl.4.3. (a) A schematic illustration of the THz emission spectrum of a dense molecular cloud core at 30 K and the atmospheric transmission from ground and airborne altitudes (adapted, with permission, from... 

GHz spectral line surveys of three regions of the W3 giant molecular cloud complex [21]. From such studies, which reveal dramatic differences in the THz spectrum of various objects, molecular astrophysicists hope to classify the evolutionary state of the cloud, just as optical spectra are used to classify stars. 

For most hnes of sight that include dense molecular clouds, the polarization spectrum beyond 2pm shows a number of features that most clearly are identified in the spectropolarimetiy of the BN object in the Orion Molecular Cloud, OMC-1, and shown in Figure 4. The main features, clearly extending above the power-law fit to the near-infrared data, are the H20-ice feature at... 

Figure 2 shows apart of the emission spectrum ofOMC-1 (Orion Molecular Cloud), a region of high-mass star formation, in the 208-232 GHz range. Many rotational lines are observed, only a few of them have been assigned by now. The rotational emission... 

A large tenuous cloud surrounds the object and is seen as a reflection nebula illuminated by the starlight that escapes above and below the ring of dust. The discovery of this object has provided dramatic evidence supporting earlier hypotheses that circum-stellar envelopes of infrared stars must be flattened. The large optical depth of the toroid produces a featureless, mid-infrared spectrum (Forrest eit 1976) but the chemical nature of the cloud has been deduced from optical spectroscopy of the reflection nebula (Crampton, Cowley and Humphreys, 1975) and by detection of a molecular cloud association with the source (Lo and Bechis, 1976 and Zuckermann ad 1976). These observations show that the 0.1 M cloud is carbon-rich, and, in fact has led to the suggestion that the source may be the progenitor of a planetary nebula. 

One very important area is the identification of molecular species in astronomical sources. A surprising number of polyatomic molecules and ions, a selection of which are listed in Table 7.1, have been identified in the so-called molecular clouds, which appear to contain regions with moderate effective temperatures (tens or even hundreds of Kelvins) and which may represent an early stage in the condensation of interstellar matter into stars. Parts of an emission spectrum from such a source arc shown in Figure 7.8. Doppler shifts of the frequencies of lines in these rotation spectra give accurate estimates of the velocities of the gas clouds relative to Earth. 

Fig. 13.2 Spectrum of the Orion molecular cloud [from W. M. Irvine and Hjalmarson, in Cosmochemistry and the Origin of Life (ed by C. Ponnamperuma, D. Reidel, 1983)]...

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