The J = 1–0 rotational transition of carbon monoxide has been used to trace the molecular gas at five different positions in the Circinus galaxy using the Australia Telescope National Facility's 22 m radio telescope at Mopra. The intensity profile of the central CO emission has a full width at half maximum of 550 pc. The 12CO (1–0) spectrum at the centre of the galaxy has an integrated temperature of 145 K km S−1, with components peaking at 0·62 K and ranging in velocity from 200–600 km S−1. The total mass of molecular gas in the Circinus galaxy, assuming that the CO intensity profile of the galaxy is similar to the radio continuum, is at least 7·5±4·1 × 108 M⊙. This estimate, combined with previously published far infrared data, yields a value for the star-forming efficiency, SFE = 16±9 L⊙ M⊙ ‒1.

We suggest and give some evidence that as an HII region expands and the O stars evolve into B giants, remains of the molecular clouds first appear as bright-rimmed clouds, then as cometary globules and finally as small clouds which are visible by the reflected light from the B giants. We propose to call the last of these ‘reflection clouds’ and all three categories collectively ‘remnant clouds’. A list is presented of about 80 objects of these remnant clouds in the Ori OB 1 association. In the Belt region there is a beautiful spatial sequence from bright-rimmed clouds through cometary globules to reflection clouds. We suspect that retarded star formation in remnant clouds can explain the presence of so-called dispersed T Tau stars in the peripheries of OB associations.

The Magellanic Clouds are unique in providing us with sites to study the interstellar medium (ISM) and its components at all scales. To promote the pursuit of such studies, we have begun the Magellanic Cloud Emission-line Survey (MCELS), a deep imaging survey of both of these nearby galaxies in the emission of Hα, [S II], and [O III]. The emission-line images will be used in detailed optical and multiwavelength studies of H II regions, supernova remnants, planetary nebulae, superbubbles, and supergiant shells. Together with parallel surveys at other wavelengths, this survey will provide the foundation upon which to build a deeper understanding of the ISM in the Clouds and other galaxies, from small scales (∼1 pc) all the way up to global scales.

We present IIIaJ, IIIaF and IVN band images of HH objects digitised from the ESO/SERC Southern Sky Survey plates. These form part of a digital image database of southern HH objects, which allows the identification of emission and reflection nebulosity and the location of the obscured sources of outflows.

The Perth Automated Supernova Search uses the 61-cm PLAT (Perth Lowell Automated Telescope) at Perth Observatory, Western Australia. Since 1993 January 1, five confirmed supernovae have been found by the search. The analysis of the first three years of data is discussed, and preliminary results presented. We find a Type Ib/c rate of 0·43±0·43 SNu, and a Type IIP rate of 0·86±0·49 SNu, where SNu are ‘supernova units’, expressed in supernovae per 1010 LB ⊙ galaxy per century. These values are for a Hubble constant of 75 kms−1 Mpc−1, and scale as (H 0/75)2.

Interferometric methods have been used at a number of observatories to improve the spatial resolution of large optical telescopes, approaching and in some cases reaching the diffraction limit. The principal methods used have been speckle interferometry and non-redundant masking (NRM). The MAPPIT (Masked APerture Plane Interference Telescope) instrument has been used for NRM observations at the 3·9 m Anglo-Australian Telescope. This paper describes a proposed instrument, MAPPIT 2, which would use a Shack-Hartmann wavefront sensor in parallel with an interferometer performing NRM or one-dimensional speckle interferometry. The inclusion of the data from the wavefront sensor will enhance the sensitivity of the instrument, especially for the imaging of relatively complex objects (those giving more than a few resolution elements with non-zero intensities). Limiting the instantaneous spatial resolution to one dimension allows available CCD detectors to operate with 100% duty cycle. Observations at a number of position angles allow two-dimensional images to be obtained.

Although a number of correlations have been demonstrated between observable parameters in galaxies, such as surface brightness, luminosity, metallicity, etc., debate continues as to which of these parameters are truly fundamental. Following a major surface photometry program and Hii region abundance analysis, we have been able to show that the surface density of recent massive star formation, the surface density of stars already formed, and the mean oxygen abundance at a given galactic radius are all fundamentally related within and between the disks of spiral galaxies. Such relationships can serve as powerful constraints on models of galactic evolution, requiring, for instance, a star formation law dependent not only on gas surface density, but also on the total mass surface density.

There are two principal problems in explaining, in terms of the emission from OB stars, the ionisation of gas which emits diffuse Hα in spiral galaxies. One is the long pathlength which the ionising photons need to traverse to reach their objectives, the other is whether sufficient photons can escape from within the H II regions which surround the hot stars. Here we treat the second point, assuming that the H II regions above a certain threshold luminosity are density bounded. We calculate the escaping Lyman continuum (Lyc) fluxes from the density bounded regions in four galaxies, and show that in each of them this is easily suffcient to produce the measured diffuse Hα emission.

We have used the TAURUS Fabry–Perot mapping spectrometer on the William Herschel telescope (WHT) to produce a complete kinematic map of the disk of M100 in Hα. Here we show how the internal velocity dispersion (σ) of the principal emission components of the brightest regions varies with their Hα luminosity. The plot shows ample scatter, but an upper envelope in σ is clearly linear (in the log–log plane) with a slope of 2·6, a result which agrees precisely with an earlier graph by Arsenault et al., who selected instead the regions of highest surface brightness. We show that this result, which differs from the conventional prediction from the virial theorem, is consistent with virialisation if the H II regions are density bounded, and thus offers evidence in support of the density bounding hypothesis for the most luminous regions in disk galaxies.

We review observations of diffuse ionised gas (DIG) in edge-on spiral galaxies. Deep imaging has revealed a variety of morphologies for ‘extraplanar’ (above the HII region layer) or ‘halo’ DIG: some show widespread prominent layers of truly diffuse gas and filamentary structures, others show just one patch or a few patches of extraplanar emission, while still others show no detectable extraplanar DIG at all. The key galactic property which appears to govern the prominence of the DIG layer is the star-formation activity. Smaller-scale connections between DIG and local star formation activity can be seen in some of the galaxies.

DIG halos are also related to radio continuum, X-ray and HI halos. Those galaxies with the most prominent DIG layers also have the most prominent radio halos. In NGC 891, there are spatial correlations between extraplanar DIG, radio emission, X-ray emission and HI, and these in turn are related to the underlying disk star-formation activity.

Progress on identifying the sources of ionisation and heating of the gas has come from spectroscopy, imaging in different emission lines, and Fabry–Perot observations. By comparing with theoretical predictions, much evidence is found for photoionisation by disk stars as the primary ionisation and heating mechanism, but recent observations are beginning to point towards the need for additional sources of ionisation and/or heating.

We present a comparison between the latest Parkes radio surveys (Filipović et al. 1995, 1996, 1997) and Hα surveys of the Magellanic Clouds (Kennicutt & Hodge 1986). We have found 180 discrete sources in common for the Large Magellanic Cloud (LMC) and 40 in the field of the Small Magellanic Cloud (SMC). Most of these sources (95%) are HII regions and supernova remnants (SNRs). A comparison of the radio and Hα flux densities shows a very good correlation and we note that many of the Magellanic Clouds SNRs are embedded in HII regions.

Cosmic radiation is capable of depositing significant quantities of energy and momentum in gravitational wave antennas at times that will generally be random with respect to gravitational signals. Such cosmic ray effects may generate noise signals at detectable levels compared to antenna design thresholds at rates of a few per year but, since antennas will not be capable of absorbing all the cosmic ray energy, it should be readily possible to construct vetoing cosmic ray detectors. For proposed interferometer antennas, a deposition of a few hundred GeV will produce a detectable noise signal and the veto will require about 100 MeV of energy deposition outside the antenna. We consider here some of the principles involved in the generation of gravitational antenna noise by cosmic ray particles and we describe a veto system to be installed at the Perth gravitational wave observatory.

A procedure is introduced to recognise sunspots automatically in solar full-disk photosphere images obtained from Huairou Solar Observing Station, National Astronomical Observatories of China. The images are first pre-processed through Gaussian algorithm. Sunspots are then recognised by the morphological Bot-hat operation and Otsu threshold. Wrong selection of sunspots is eliminated by a criterion of sunspot properties. Besides, in order to calculate the sunspots areas and the solar centre, the solar limb is extracted by a procedure using morphological closing and erosion operations and setting an adaptive threshold. Results of sunspot recognition reveal that the number of the sunspots detected by our procedure has a quite good agreement with the manual method. The sunspot recognition rate is 95% and error rate is 1.2%. The sunspot areas calculated by our method have high correlation (95%) with the area data from the United States Air Force/National Oceanic and Atmospheric Administration (USAF/NOAA).