New measurements of the galactic background radiation between 151 and 1407 MHz have been made by Sironi and by Webster. The radio spectrum shows a bend at ~ 315 MHz in Bridle's Region I and ~ 100 MHz in Region II, implying magnetic fields of 7.6 µG and 2.4 µG, respectively.

The galactic background radiation at 4.2 and 15.5 GHz was observed with a resolution of 11′ at nine points on the galactic equator free of confusion from discrete sources. Relative amounts of thermal and nonthermal radiation were determined, and conditions in the interstellar gas are discussed.

Both maser emission and thermal emission and absorption have been observed from the rotationally excited 2π3/2, J = 5/2 and 2π1/2, J = 1/2 states of OH. Conditions in the interstellar gas are discussed.

The structure and physics of Hiiregions are reviewed. The discussion is principally based on the radio mapping of intermediate-size Hiiregions to measure the energy balance, the mapping of small-scale structure by aperture-synthesis techniques to define the ionization conditions, and determination of helium abundances from radio recombination-line observations of H and He in Hiiregions.

Westerbork observations of several large Hiiregions in the Cygnus-X region are described. IC 1318 appears to be a giant Hiiregion, and two nearby sources may be genetically related to it.

The Westerbork Synthesis Radio Telescope was used to map the continuum radiation of M33 at 1415 MHz. Of 67 radio sources with fluxes S> 1.8 mJy (3σ), 60% coincide with Hα sources. These are all intrinsically stronger than 4 × the Orion nebula, i.e., they are giant Hiiregions. The two strongest sources, NGC 604 (58 mJy) and NGC 595 (20 mJy), are similar to W51.

The luminosity of the brightest Hiiregions of M31 was determined with the NRAO 3-element interferometer at 3.7 cm and 11 cm wavelength. It is unlikely that M31 has any superbright Hiiregions such as W51 or W49; our Galaxy has between 10 and 20 Hiiregions that are more luminous than any in M31.

The 4.1-mm continuum emission shows a peak at the Trapezium stars and an extension to the west, where the molecular and IR sources are. The 4-mm line of para-formaldehyde has a similar distribution to that of the 3-mm line of HCN and extends more to the north than the 2-mm line of ortho-formaldehyde. This probably means a lower temperature in the northern part of the cloud.

Radio recombination line observations of the Carina nebula at 6 cm and 3.4 cm were made at Parkes. Around Carina II the profiles are separated by as much as 45 km s-1. This is interpreted as expansion in the H ii region.

The results of new studies of decimeter wavelength Hnα and Cnα lines toward galactic nebulae are reported. The observations were made with the 305-m radio telescope of the Arecibo Observatory at 430 MHz (247α and 248α) and 606 MHz (221α). Selected positions in W51, W49, and the Rosette nebula were observed. The observed lines exhibit no pressure broadening; however, this is consistent with the interpretation of the data.

This paper reviews recent optical results on the large scale distribution of ionized gas in spiral galaxies, including our own. There is a diffuse, inhomogeneous emission in the arm region in spirals, including our Galaxy, and in gas-rich galaxies a fainter diffuse emission between the arms.

The distribution of the dust is found by comparing 3-cm brightness temperatures, Hα surface brightness, and Hβ surface brightness. The dust is probably mixed with the gas. The Balmer radiation originates in front of the dark bay.

Most Hii regions emit large amounts of energy at infrared wavelengths. Dust grains absorb a major fraction of the total energy emitted by the O stars, and this is reradiated in the infrared. The dense Hiicondensations seen by aperture synthesis radio observations are strong 20-µm infrared sources. The dust is probably mixed with the ionized gas in these sources. There are also infrared sources that are not radio sources; these may be protostars. Infrared emission has also been found from many OH/H2O maser sources associated with Hiiregions.

When OH and H2O sources are found in Hii regions, a compact source of radio continuum and infrared emission is usually, perhaps always, found nearby, < 1017 cm away (approximately the conjectured size of a prestellar condensation). Whether the masers are self-excited, are amplifying the background radiation, or are themselves associated with an exciting star is clearly model-dependent, and observations have not yet given the answer. H2O masers occur less frequently than OH masers. When they occur together they appear as a cluster of compact sources of line radiation, exhibiting the same range of radial velocities, The OH sources nearly always are strongly polarized, while the H2O maser is not. Both classes of maser are probably saturated, and some care is needed in inferring the maser geometry from the observations. The period of stability of neither OH nor H2O can be much more than 103 yr, and this fact can be used as an estimator of stellar formation rate.

Observations of Class I OH maser sources show a range of features which are predicted on the basis of Zeeman splitting in a source magnetic field. Magnetic field strengths of 2 to 7 mG are derived for eight OH maser sources. The fields in all the clouds are directed in the sense of galactic rotation. A model of W3 OH is proposed which incorporates the magnetic field data. It is shown that no large amount of magnetic flux or angular momentum has been lost since the condensation from the interstellar medium began.

The first spectra of southern H2O masers obtained with the 14-m Itapetinga radio telescope are described. A new H2O source was found in H2-3 (G345.4 − 0.9).

The velocity structure of OH profiles of OH maser regions is used to estimate the time scales of the source distributions. Time scales are found to be of the order of a few thousand years in typical cases. The velocity dispersions and intensity distribution of components are interpreted in terms of a collapsing cloud model of the emission regions. The masses of the clouds are found to be in the range from a few solar masses to a few hundred solar masses for the well-known emission regions.

Narrow OH emission lines at 1667 MHz, apparently from a Class I source, have been observed near the reflection nebula NGC 2071. The region contains many T Tauri stars. OH emission corresponding to the dust cloud north and east of NGC 2024 is also seen. At 1720 MHz the dust cloud component appears in absorption; presumably the isotropic 2.7 K cosmic background is being absorbed.

Observations have revealed the presence of inhomogeneities in both density and velocity in Hiiregions. Dense non-ionized condensations can persist for a long time, developing bright rims of dense ionized gas around them. Attempts have been made to understand the large ~50 km s-1 motions seen in some Hiiregions by invoking stellar winds or the flow of cosmic ray particles through the plasma.

A supernova event may lead to four observable features: a pulsar, an expanding nebulosity, a radio source and an X-ray source. The great majority of supernovae do not produce observable pulsars, and discussion is restricted largely to the other features. An increasing number of X-ray sources is now being detected and the structure and spectrum of the stronger sources investigated; these observations yield information about the physical state of the remnant. Recently, 11 new optical and radio remnants have been found in the Magellanic Clouds. These have led to a good determination of the Σ – D relation, thus providing a more reliable distance scale for galactic SNR, but have also shown that a one-to-one correspondence between a radio source and a supernova event is questionable. When these remnants are combined with corrected earlier catalogues and a new southern catalogue containing a high proportion of distant old remnants the number of known SNR is about 150. The evolution of galactic SNR may be investigated empirically, and although the derived rate of occurrence is very uncertain a rate of about 2 supernovae per century is consistent with most determinations. The galactic SNR are distributed rather like the radio disc emission, but more closely confined to the galactic plane, and selected SNR show evidence of a spiral pattern.