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A compilation of CO emission regions and their measured parameters is presented which represents a nearly complete accounting of the molecular clouds in the first quadrant of the Galaxy. Emission regions associated with radio H II regions have systematically brighter CO peaks that are a factor of two to three times larger and have twice the mean velocity dispersion as the general cloud population. Both the H II region clouds and the hot core regions have a Galactic distribution characteristic of a spiral arm population, whereas the colder clouds are much less confined in Galactic azimuthal angle. Virial masses are obtained for the large sample of clouds with assigned kinematic distances. The mean H2 density for a GMC of diameter 40 pc is 180/cm. For these clouds, a linear relationship is found between the H2 column density and the integrated CO emission. The variation in the Z-dispersion of clouds as a function of cloud mass suggests that more massive GMCs have smaller random velocities.

We have detected v = 1, J = 5-4 SiO maser emission from R Leo, chi Cyg, and VX Sgr and v = 2, J = 4-5 maser emission from VX Sgr. Upper limits are reported for maser emission in the J = 6-5, v = 1 and v = 2, and J = 2-1, v = 3 transitions toward several late-type stars. Maser photon emission rates for the high J transitions which have been detected are roughly comparable to emission rates for the lower J transitions. Various maser pump mechanisms and emission regions are discussed, and published numerical models are compared with the observations. No single model emerges as the best explanation of SiO maser phenomena.

Optical and near-infrared photometry in the VRIJHK and CO (2.35 microns) bands and optical spectroscopy and polarimetry reveal that the optical counterpart of the X-ray source H0253+193 is most likely a RS CVn binary system. The results show a visual extinction of 11.3 mag to the star, with an IR excess possibly due a cooler binary companion or circumstellar material. It is suggested that the I-band polarization of 8.1 + or - 1.8 may be induced in the starlight by passage through the molecular cloud. The lack of strong H-alpha emission in the optical spectrum argues against the possibility of a classical T Tauri star, and the IR excess argues against a naked T Tauri star. The wide energy spectrum found in the dereddened optical and near-infrared photometry supports the binary star model.

J = 1-0 and 2-1 (C-12)O and (C-13)O emission has been observed over the L204 dark cloud complex, and optical polarization measurements of background stars have been made along the length of the cloud. The CO radial velocities exhibit gradients along the length of the complex which mimic the variations in the mass distribution, and the polarization E vectors suggest that L204 contains a magnetic field predominantly perpendicular to its long dimension. These observations suggest that some external impulse acted on the complex over a large angular extent and that the subsequent evolution of the cloud has been controlled to a considerable extent by a magnetic field. Assuming virial equilibrium, an approximate value for the magnetic field in L204 is 50 micro-G. 29 references.

The sites of massive star formation in molecular clouds are investigated by comparing high-resolution radio surveys of molecular and ionized gas emission in the Milky Way. CO emission maps from the Massachusetts-Stony Brook survey of the first Galactic quadrant are used to locate, in l, b, and v, the molecular clouds associated with radio recombination-line H II regions. It is found that the radio H II regions are typically associated with giant molecular clouds (GMCs) with diameters of 20-60 pc and virial masses of 100,000 to a million solar masses. The radio H II regions appear preferentially concentrated toward the centers of the GMCs, contrary to the 'blister' picture of massive star formation on cloud surfaces.

Le programme consiste en 40551 spectres obtenus dans le domaine des longitudes l=8°-90° de b=1,05° a b=+1,0°. On presente les donnees reduites sous la forme de cartes de contour latitude-vitesse (B, V) a chaque longitude. On peut detecter tous les nuages de plus de ∼15 pc de diametre dans l'anneau de nuages moleculaires R=0,4-0,8 R ○. . On peut obtenir directement a partir des cartes, les temperatures et les dimensions d'environ 3000 nuages moleculaires

Observational evidence is presented for the compression of molecular gas in the interface between colliding GMCs, and it is proposed that this is the dominant mode for high-mass star formation in the Galaxy. For a sample of 94 GMCs associated with high-luminosity radio H II regions, the efficiency of OB star formation decreases significantly with increasing cloud mass over the observed mass range. It is concluded that star formation is generally not stimulated by an internal mechanism. The formation of OB stars by cloud-cloud collisions is suggested by the observed quadratic dependence of the Galactic H II region distribution on the local density of H2. The preference for OB star formation in spiral arms is then naturally accounted for by orbit crowding and the increased collision frequency of clouds in the spiral arms.

This paper describes a polarimeter for use at wavelengths near 1 mm, designed to be self-contained and portable. Only minor modifications should be required to adapt this instrument for use on any of several millimeter and submillimeter telescopes. The polarimeter system and data-taking techniques are described, and a preliminary measurement is reported of the polarized dust emission from the Orion KL region at 1.3 mm using the NRAO 12 m telescope. The results are similar to previous polarization measurements of Orion at far-infrared and submillimeter wavelengths. The magnetic field direction implied by the polarization position angle is parallel to that found in the surrounding Orion region using optical and near- to midinfrared polarimetric techniques. 17 references.

Observations of 115 GHz (J = 1-0) emission from the CO molecule for the southern galactic plane from longitude 294/sup 0/ to the galactic center are compared with northern galactic plane observations to longitude 86/sup 0/. The longitude distribution of integrated emission is similar in the two hemispheres exhibiting broad peaks centered at about l = +- 25/sup 0/; the strong galactic center feature is confined to l = +- 2/sup 0/. The computed radial distribution of CO emissivity averaged over both hemispheres has a peak value of 12 K km s/sup -1/ kpc/sup -1/ at galactocentric radius R = 0.5 iR/sub sun/, which is 3-4 times that at R = 0.2 and 0.9 R/sub sun/. In the south the distribution has an approximately constant CO emissivity between 0.25 and 0.85 R/sub sun/; in the north it is sharply peaked between 0.45 and 0.65 R/sub sun/. The integrated CO emissivity in the south is about 20% larger than that in the north. Factors of 1.5-2.5 difference in the north and south emissivities at R = 0.2, 0.5, and 0.8 R/sub sun/ may be due to spiral arms or ring segments.