Orion, molecular cloud

Figure 5.1 The Orion molecular cloud. (Reproduced by courtesy of Ronn Magdalena, NRAO)...

There are some variations in the composition of chemical clouds as they evolve in time from dark clouds such as TMC-1 to giant molecular clouds such as Orion where the presence of light from young stars initiates photochemistry. The Orion molecular cloud chemical inventory contains several saturated species such as ethanol (CH3CH2OH) and its CN analogue (CH3CH2CN), the simplest carboxylic acid (CH3COOH, acetic acid) and methylamine (CH3 NH2). 

Giant molecular clouds the GMCs have a lifetime of order 106—10s years and are the regions of new star formation. The Orion nebula (Orion molecular cloud, OMC) is some 50 ly in diameter and 1500 ly from Earth. The temperature within the cloud is of order 10 K and the atomic density is 106 cm-3. The chemical composition is diverse and contains small diatomic molecules, large polyatomic molecules and dust particles covered with a thick ice mantle. 

Fig. 6.1. Stellar nursery in the constellation of Orion. Molecular clouds A and B were detected by their radio emissions. They appear to have given birth to several generations of stars (la, It and Ic).

Hydrogen chloride is the first chlorine-bearing interstellar molecule to have been detected. Its lowest rotational transition (J = 1 -> 0) at 625.9 GHz has been observed in the Orion Molecular Cloud (OMC-1) in emission with the Kuiper Airborne Observatory, (Blake, Keene, and Phillips, 1985) since atmospheric opacity at this... 

Table 3. Molecules Detected in the Orion Molecular Cloud (OMCl) and the Taurus Molecular Cloud (TMC1)...

Typical kinetic gas temperatures in dense interstellar clouds are 7k < 30 °K but may in some cases reach values of v 80 °K (e. g. the Orion molecular cloud). The relation between excitation temperature Tex and kinetic gas temperature 7k is further discussed in Sections III. E and III. F. 

Wilson et al. (1972) have recently reported the first positive 1SN isotopic detection in an astronomical source. They observed in the Orion molecular cloud the J = 2 -> 1 transitions of the rare hydrogen cyanide isotopic species H13C14N and H12C15N whose rest frequencies are 172677.7 MHz and 172108.1 MHz, respectively (Winnewisser et al., 1971). For these two molecules and in almost all the other isotopic abundance determinations, which can presently be given only with large error margins ( 20 %—50%), the isotopic ratios are found to have essentially terrestrial values. 

Tatfe 6. Molecules Detwted in the Orion Molecular cloud and the Taurus Molecular cloud... 

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. 

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 11. A circular polarization image at 2.2 im of the star-forming region in the Orion Molecular Cloud, OMC-1 [59], Light and dark patches represent alternate signs of circular polarization. The main source (not visible in the image) is the IRC2 complex at position (0,0).

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... 

HL < m < 10 I /year are found. Flg. 5 shows a broadwing-emission profile of CO towards the Orion molecular cloud. 

Stacey et al. 1982, Watson et al. 1985), and of vibrationally excited CO (Geballe and Garden 1987) in the Orion molecular cloud. 

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)]...

The Orion Molecular Cloud (OMC-1) is perhaps the best studied galactic region of recent star formation. The magnetic field has been measured in the cloud by a variety of methods. All of these methods show that the weakest... 

Abstract. Neai-in aied imaging of the Orion Molecular Cloud has revealed that an explosive event occurred in its core within the past 1000 years, ejecting at least a score of dense knots of gets at several 100 km/s. 

The images provide persuasive evidence for an explosive event in the core of the Orion molecular cloud, ejecting shrapnel over a wide opening angle, and originating from or near IEc2. They support the interstellar bullet ... 

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