Radio Observations

In dark clouds the dust protects the molecules from dissociation by UV radiation. This protection is presumably even better in the case of Scoville s black 

Radiation intensities are referred to the radiation of a black body. In the radio frequency range it is convenient to express line intensities in equivalent line brightness temperatures, since the surface brightness Bv of a black body 

In radio astronomy multichannel or autocorrelation (Fourier) spectrometers are used which simultaneously cover the whole line profile. Consider a molecular cloud observed against a source of continuum radiation of a given brightness temperature. The continuum brightness temperature is the sum of the 2.7 °K isotropic background radiation Tbh of a continuum source (such as an HII region or a supernova remnant) which may be in the line of sight and located behind the molecular cloud. A specific molecular transition with optical 

the first term represents the line emission proper from the molecular cloud. The second term describes the attenuation of the continuum radiation due to absorption by the molecules. 

With the center frequency of the spectrometer shifted outside the line profiles the measurement yields the unattenuated continuum temperature 

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Biver N ef a/1997 Evolution of the outgassing of oomet Flale-Bopp (C/1995 01) from radio observations Science 275 1915-18... 

The radio observations (Hogg, 1982) are in agreement with the results of our analysis, but do not help to restrict the one-dimensional variety of solutions of the analysis to an unique set of parameters. 

In this contribution, we first examine the known mass-loss mechanisms in the light of the recent observations(Sect.II),and then we review some recent infrared and radio observations that may be relevant to our understanding of the outer atmospheric structure and mass-loss phenomena(Sect.Ill). Based on these observations, new picture of the outer atmosphere of red (super)giant stars is proposed and its implications on circumstellar chemistry as well as on mass-loss phenomena are discussed(Sect.IV). 

Distance Determination of Mass Losing Carbon Stars from CO and HCN Radio Observations... 

Abstract A method of distance determination of evolved carbon stars is proposed and applied to six stars for which the terminal velocity of expansion and the angular size are obtained from the CO and HCN radio observations made at the Nobeyama Radio Observatory. The method assumes the radiation driven wind in spherical geometry. Within those small samples, however, two types of mass losing stars that are systematically different in the antenna temperature ratio Ta(CO)/T/i(HCN) 1, in the velocity ratio u(CO)/u(HCN) l, and in the angular size ratio 0(CO)/0(HCN) 1 seem to be present, suggesting nonspherical geometry of the outflow. 

Infrared and radio observations of the circumstellar envelope have been exploited very successfully. The most commonly studied molecule is CO hundreds of nearby stars are known CO sources (Nyman et al. 1992). Additionally, over 50 different species have now been detected in various circumstellar envelopes (Olofsson 1992). 

The M87 core shows remarkable structures (Fig. 2.9) including the counterjet cavity and a bubble (labeled bud in Fig. 2.9) erupting from the counterjet cavity, corresponding to the southeastern extension of the bright core in the 6 cm radio observations of Hines et al. (1989). 

The sun is located near the edge of the arm O. It may be noted that this picture of the spiral structure in the vicinity of the sun is based on both optical and radio observations, whereas the large scale structure of the interstellar gas (Fig. 4) is based only on observations of the X21 cm hydrogen line and kinematic distances, which become highly uncertain towards the galactic center and anticenter. Kinematic distances are obtained from a model for the rotation of the Galaxy due to Schmidt. This model relates the circular orbital velocity of the gas to the distance from the galactic center (see Fig. 3). 

In contrast to radio observations by which dense clouds are investigated, optical observations yield information on dilute clouds only. Both methods yield column densities and from these values space densities can be estimated. Such results show that CO is probably next to H2 the most abundant molecule, whereas OH and H2CO though not the most abundant molecules seem to be most widely distributed. Some of the more complex molecules are just barely detectable by present radio techniques. Improved experimental techniques will be paralleled by the detection of other molecules. 

Part B Radio Telescopes Part C Radio Observations Edited by M. L Weeks... 

RADIO OBSERVATIONS OF HII REGIONS AND SOME RELATED THEORETICAL WORK... 

A special symposium on "HII regions and related topics" which summarizes radio observations of HII regions up to 1974 was held in Mittelberg, Austria, January 13 through 17, 1975. The proceedings of this symposium are published and will be referred to as (1975 Lect. Notes Phys. 42). In the following Sect. II (radio continuum) and III (radio recombination lines) we try to emphasize recent observational results not yet covered in these proceedings. 

Radio observations of HII regions in external galaxies are reviewed by Israel (1975, Lect. Notes Phys. 42, p. 288). Comparison of radio and optical observations show, that these HII regions contain large amounts of dust. 

The Center for Astrophysics - University of Arizona 102-cm balloon-borne telescope was used to produce high resolution ( ) maps of the HII regions M17, M20, NGC 7538, and the Galactic Center. These maps will be presented and their relationship to ground-based infrared and radio observations /ill be discussed. 

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