The galactic plane between longitudes 326 0 and 340 0 has been searched for OH emiSSIOn and absorption on the 1665 and 1667 MHz transitions. Forty main-line emission sources were detected (27 new ones, 13 previously known), and these constitute a sample complete to a weIl-defined lower intensity limit in this region of sky. Line profiles of all sources are shown and the statistics on variability and on the intensity ratios of the ground state transitions are summarized. The completeness of the sample encouraged us to make a first attempt to construct a luminosity function and to estimate the total number of such masers in our Galaxy. A study of the velocity structures showed these to be extremely varied, but none exceed a total range of 25 km s -1; combined velocity and polarization data are compatible with a Zeeman splitting origin for the circular polarization, and with this interpretation several sources yield an estimate for the line-of-sight magnetic field strength of a few mG. Preliminary investigations of the associations with other celestial objects indicate that many of the masers are loosely associated with HII region complexes, but in at least eight instances no HII regions have yet been detected; of these eight masers, two may be associated with supernova remnants and one with an unidentified nonthermal radio source. IntroductionMost searches for OH line radiation on the 1665 and 1667 MHz transitions have been made at the positions of other objects of interest, e.g. HII regions, dust clouds and various types of stars. However, it is clearly desirable to make unbiased OH searches in order to obtain a clearer guide to the frequency of occurrence of different classes of OH source; a small survey of this kind, resulting in the detection of four OH masers, was conducted by Ellder et al. (1969). The search reported here, conducted along the galactic plane between longitudes 326° and 340°, detected 400H masers. This main-line search complements our earlier satellite-line searches over the same region (Caswell and Haynes 1975, hereafter referred to as CH; Haynes and Caswell 1977, hereafter He), and these earlier surveys facilitated the classification of the new sources. We propose to make similar surveys of other portions of the Galaxy.

An extensive 22 GHz survey of H 2 0 masers has been made with the Parkes 64 m radio telescope. We present data here for 68 sources, of which almost one-half were discovered in the present series of observations. The telescope beamsize, 100' arc to half-power, has enabled us to improve the position measurements of most of the known sources and in a few cases has allowed us to resolve a 'source' into several spatially separated components. The wide velocity coverage of our observations (> 200 km s -1) has led to the discovery of several interesting new high-velocity features. In addition to details for each source, the general properties of the sample are discussed. In the typical interval of 8 months between successive observations, the peak intensity of many sources varied only slightly (by less than a factor of 2); a few sources, however, showed more dramatic variations.

Aust. J. Phys., 1983,36, 361-99 The galactic plane from longitude 340° through the galactic centre to longitude + 2° has been searched for OH on the 1665 MHz transition. Forty-nine OH maser emission sources were detected and these have now been studied on all four OH ground-state transitions. Most of the masers are associated with regions of star formation (type I) while three may be examples of late-type stars (type II OH/IR) with unusually strong main-line emission.Two especially interesting type I masers discovered are: OH351·78-0·54, which is now the strongest OH maser known, with a peak intensity of nearly 1000 Jy (= 10-23 W m-2 Hz-i), and OH340·78-0·1O, which displays an unusual velocity structure suggestive of a shell of emission.Combining the present results with those of our earlier survey of longitudes 326° to 340 0 (Part I) doubles the number of well-studied type I OH sources. We have thus been able to improve our previous estimate of the luminosity function and have also now derived a galactic radial distribution extending to the galactic centre; this shows that while the inner 5 kpc of the Galaxy is generally deficient in type I OH masers, the immediate vicinity of the centre has a quite high density of such sources.The conclusions of Part I were reassessed in the light of the new results. In the total sample of 85 type I sources six show accompanying strong 1720 MHz maser emission and nine show strong 1612 MHz maser emission; this significantly alters the statistics of Part I alone, which showed no 1720 MHz masers but six 1612 MHz masers. However, our earlier results regarding velocity structure, polarization and variability are generally corroborated; in particular, the present data reinforce our conclusions that a surprisingly large proportion of masers (including the exceptionally strong OH351'78-0'54) have no closely rdated prominent HII region and quite likely pinpoint sites of the very early stages in star formation. The quite common occurrence of the masers within extensive OH clouds (as indicated by weak but spatially extended emission at 1612 or 1720 MHz) is also suggestive of dense molecular clouds in which star formation and HII region development are just beginning.

Abstract. The total and polarized radio continuum emission of 20 barred galaxies was observed with the Very Large Array (VLA) at λ3, 6, 18 and 22 cm and with the Australia Telescope Compact Array (ATCA) at λ6 cm and 13 cm. Maps at 30 angular resolution are presented here. Polarized emission (and therefore a large-scale regular magnetic field) was detected in 17 galaxies. Most galaxies of our sample are similar to non-barred galaxies with respect to the radio/far-infrared flux correlation and equipartition strength of the total magnetic field. Galaxies with highly elongated bars are not always radio-bright. We discuss the correlation of radio properties with the aspect ratio of the bar and other measures of the bar strength. We introduce a new measure of the bar strength, Λ, related to the quadrupole moment of the bar's gravitational potential. The radio surface brightness I of the barred galaxies in our sample is correlated with Λ, I ∝ Λ 0.4±0.1 , and thus is highest in galaxies with a long bar where the velocity field is distorted by the bar over a large fraction of the disc. In these galaxies, the pattern of the regular field is significantly different from that in non-barred galaxies. In particular, field enhancements occur upstream of the dust lanes where the field lines are oriented at large angles to the bar's major axis. Polarized radio emission seems to be a good indicator of large-scale non-axisymmetric motions.

Seventy five maps are presented showing the 5 GHz emission from the galactic plane in the range I = 190� ~ 360� .... 40� for - 2� < b < 2� (an area of approximately 600 square egrees). The method of observing and the computer reduction of the data are discussed. the telescope resolution is 4'�1 arc to half-power points and the detection limit for point sources is better than 0�5 Jy.

The discovery of three new H20 sources associated with HII regions is reported. Observations of other southern H20 sources show, in several instances, considerable intensity changes over a 20-month interval.

Aust. J. Phys., 1983,36,417-42 We tabulate all 55 OH main-line masers discovered to date in the galactic plane between longitude 3° and 60°. For most of these we show current spectra, which have been taken with the Parkes 64 m radio telescope, in both senses of circular polarization on the 1665 MHz and/or 1667 MHz transitions; for some sources we give new position estimates, and several sources are reported for the first time. We discuss many sources individually and note that while most of the main-line OH masers probably pinpoint compact HII regions and sites of current star formation, a few appear to be unusual varieties occurring in circumstellar shells, possibly associated with late-type stars.The 55 sources are approximately half as many as those found in the Parkes survey of the complementary southern region; this reflects the lower sensitivity and less uniform coverage of the northern surveys on which the present atlas is largely based and precludes its use in the study of the galactic distribution of OH masers. However, following our present measurements, the sources have become a valuable addition to the sample for studying associations with HII regions and H 2 0 masers, polarization and velocity structure, relative line intensities and variability. IntroductionIn the decade following the discovery of OH maser emission, effort was largely concentrated on searching for emission from specific astronomical objects such as HII regions, late-type stars and planetary nebulae.In the case of main-line OH masers, which are commonly associated with sites of star formation and young HII regions, systematic surveys have now been made with the Parkes 64 m telescope (beam size 12' arc at 18 cm wavelength) over the longitude range 300° -+ 360° -+ 2° along the galactic plane (b ~ ±Oo. 3, with wider coverage where the radio continuum emission indicates much greater thickness of the plane). The surveys extend to masers slightly weaker than 1 Jy (=1O-26 Wm-2 Rz-1 ), and most masers have been positioned with Lm.s. uncertainties of <30".

A search for OH at 1612 MHz has been made along the galactic plane from longitude 340 0 to the galactic centre, yielding 78 emission sources (mostly new discoveries); a further 5 sources have been found in a less sensitive survey between longitudes 270 0 and 326Of these 83 sources 55 are masers of the variety showing two intensity peaks spaced in velocity-a characteristic of OH/IR stars. The velocity and spatial distributions of these new OHjIR stars (which are not as yet identified in the optical or infrared) are discussed, with special reference to their kinematic properties and population type; it is still not clear whether they are predominantly late-type giants (Mira variables) or supergiants. The other 28 OH sources detected include 11 of the type lIe variety (extended OH clouds exhibiting 1612 MHz emission with accompanying 1720 MHz absorption) and 4 with accompanying main-line (type 1) OH masers; the remaining 13 sources do not readily fit within existing classification schemes and are discussed individually.