Showing papers by "Charles H. Townes published in 1981"

Detection of interstellar OH in the far-infrared

Abstract: Strong absorption lines of OH have been detected at wavelengths of 119.23 and 119.44 microns in the direction of Sgr B2. The lines arise from the 2Pi3/2, J = 5/2-3/2 transitions and imply a column density of N(OH) not less than 2.7 x 10 to the 15th/sq cm. The LSR Doppler velocity of the absorption features is close to zero; this suggests that material is being seen from both the +62 km/s and -90 km/s clouds at radio wavelengths. In addition, the detection of the same two lines in emission from the shocked region of the Orion Nebula has been made possible. The indicated intensity of these lines is 1.6 x 10 to the -17th W/sq cm, which implies a column density of shocked OH of about 3.6 x 10 to the 15th/sq cm.

Far-infrared observations of shocked CO in Orion

Abstract: The J = 27-26 and J = 30-29 transitions of CO have been detected in the Orion molecular cloud. These detections, together with an improved measurement of the J = 21-20 transition, allow estimation of the temperature and density of the shocked material and the fractional abundance of CO. By solving the equations of detailed balance for J less than or equal to 50 and fitting the data to a two-component model consistent with earlier 2-micron and 12-micron H2 observations, it is shown that the hot (2000 K) component has a density of approximately 1.0 x 10 to the 6th/cu cm, while the cooler component lies in the range of 400-1000 K and is 2-5 times more dense. Approximately 25% of the carbon is in the form of CO. The spatial extent of the hot CO has also been examined by observing the J = 21-20 transition at a number of positions, and it is found to be distributed similarly to the H2 lines. In addition, a search for J = 21-20 and J = 22-21 CO emission from six other sources has resulted in 3-standard-deviation upper limits of a factor of 10 below the intensity of the Orion lines.

The abundances of neon, sulfur, and argon in planetary nebulae

Abstract: 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.

Far-infrared (O III) and (N III) line emission from galactic H II regions and planetary nebulae.

Abstract: Measurements of O/sup + +/ and N/sup + +/ fine structure lines in several galactic H II regions and planetary nebulae are reported. Emission from (OIII) 51.8 ..mu..m was detected in the diffuse nebulae M17, W43, W49, W51, and NGC 7538, and marginally in the planetary nebulae NGC 6543, with upper limits obtained for the compact H II region DR 21 and the planetary nebulae M57 (NGC 6720) and NGC 7027. The (N III) 57.3 ..mu..m line was detected in M17 and W51. Preliminary maps were made of M17 and W51 in the (OIII) line, and of M17 in the (N III) 57.3 ..mu..m line. We combine the present results with previous (OIII)88.4 ..mu..m data to obtain electron densities in M17, W49, W51, and NGC 7538, and N/sup + +//O/sup + +/ abundance ratios in M17 and W51. The implications of these measurements with regard to the ionization conditions in the nebulae are discussed.

High spectral and spatial resolution observations of the 12.28 micron emission from H2 in the Orion molecular cloud

Abstract: The pure rotational S(2) line of molecular hydrogen at 12.28 microns was looked for in 44 positions in the Orion moleular cloud with 6 in. beams and 35 km/s spectral resolution; it was detected in 27 positions. Emission was observed over a velocity range of + or - 100 km/s. 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 seen in the 2 micron hydrogen transitions. However, unexpectedly complex line profiles and point-to-point variations in linear shapes appear, particularly in the region near IRc9.

Detection of forbidden line O I 63 micron emission from the galactic center

Abstract: The detection of the 63 microns line of [O I] is reported for three positions in the H II region complex Sgr A at the galactic center Velocity resolution of the line indicates that the emitting material has both rotational and radial motion of magnitude similar to that of the ionized gas in the core and that a substantial amount of the emitting material lies within the central few parsecs of the Galaxy A model in which [O I] is collisionally excited by neutral hydrogen, either from the warm region ahead of an ionization front or behind a shock, is proposed and gives a total mass of hot, neutral gas within the central 3 pc of the Galaxy of between 10 and 10(exp 3) solar mass A limit on the flux of this line has been set for Sgr B2

VLA observations of DR 21 NH3 /1, 1/ absorption - Direct evidence for clumping

Abstract: The (1,1) transition of NH/sub 3/ was observed in absorption against DR 21 with a synthesized beam of 2'' size at the VLA The DR 21 continuum is resolved by the VLA into components distributed within a range of about 30'', but only the brightest (and most southerly) component is absorbed by NH/sub 3/ The indicated filling factor and optical depth of the absorption feature are consistent with a model suggested by emission results, ammonia existing in optically thick thermalized clumps One of these would be producing the observed absorption

Multiple telescope infrared interferometry

Abstract: The advantages of multiple telescope infrared interferometry are discussed in detail, using the 10 micron region as a specific example Scale and seeing considerations are addressed, taking into account analytically the distorting effect of turbulent air and discussing the effect of water vapor on seeing The usefulness of fringe phase determination to determine the intensities in the radiation field, and the effect of atmospheric fluctuations on their use, are considered Astrometry by means of interferometry is extensively covered, with examples such as a plot of the fringe phase of o Ceti as a function of time compared with a theoretical fringe phase of the star with a fixed best-fit baseline The sensitivity of an interferometer involving two receiving telescopes is considered Finally, an example of a telescope design for 10-micron interferometry is described and depicted