Beam-driven Langmuir waves in the solar wind are generated just above the electron plasma frequency, which fluctuates in the inhomogeneous solar wind plasma. Consequently, propagating Langmuir waves encounter regions in which the wave frequency is less than the local plasma frequency, where they can be reflected, mode converted to transverse electromagnetic waves, and trapped in density wells. The aim here is to investigate Langmuir wave reflection and mode conversion at a linear density gradient for typical solar wind parameters. It is shown that higher mode conversion efficiencies are possible than previously calculated, but that mode conversion occurs in a smaller region of parameter space. In addition, the possibility of detecting mode conversion with in situ spacecraft Langmuir wave observations is discussed.

The surface of the Sun is continually oscillating due to sound waves encroaching on it from the interior. Measurements of the surface velocity are used to infer some of the properties of the regions through which the sound waves have propagated. Traditionally, this has been done by using a modal decomposition of the surface disturbances. However, the use of ray descriptions, in the form of acoustic holography or time–distance helioseismology, provides an alternative approach which may reveal more detailed information about the properties of local phenomena such as sunspots and active regions. Fundamental to any such treatment is determining the correct ray paths in a given atmosphere. In the simplest approach, the ray paths are constructed to minimise the travel time between two points (Fermat's principle). However, such an approach is only valid in the high frequency limit, ω » ωc, N, where ωc is the acoustic cut-off and N the Brunt-VÄisÄlÄ frequency. Although ωc is often included in time– distance calculations, and N occasionally, the same is not true of acoustic holography. We argue that this raises concerns about image sharpness. As illustrations, representative ray paths are integrated in a realistic solar model to show that the Fermat approximation performs poorly for frequencies of helioseismic interest. We also briefly discuss the importance of the Brunt-VÄisÄlÄ frequency to the time–distance diagram.

Various dynamically important extragalactic large-scale structures in the local Universe lie behind the Milky Way. Most of these structures (predicted and unexpected) have only recently been made ‘visible’ through dedicated deep surveys at various wavelengths. The wide range of observational searches (optical, near infrared, far infrared, radio and X-ray) for galaxies in the Zone of Avoidance (ZOA) will be reviewed and the uncovered and suspected large-scale structures summarised. Particular emphasis is given to the Great Attractor region where the existence of yet another cluster is suspected (Woudt 1998). Predictions from reconstructions of the density field in the ZOA are discussed and compared with observational evidence. Although no major structures are predicted out to about v ≲ 10,000 km s−1 for which no observational evidence exists, the comparison between reconstructed density fields and the observed galaxy distribution remain important as they allow derivations of the density and biasing parameters.

Amongst our sample of radio-excess IRAS galaxies, we have identified compact steep spectrum radio sources that fall into the classes of CSS or GPS sources, but have not previously been identified as such. The sample includes objects that have radio powers as low as ˜1022 W Hz−1. We suggest that these are low-power analogues of CSS and GPS sources, with weaker radio jets. These may be precursors to FR I radio galaxies or may ‘fade’ into radio-quiet galaxies.

In this paper we discuss abundance ratios and their relation to stellar nucleosynthesis and other parameters of chemical evolution models, reviewing and clarifying the correct use of the observed abundance ratios in several astrophysical contexts. In particular, we start from the well-known fact that abundance ratios depend on stellar yields, initial mass function, and stellar lifetimes, and we show, by means of specific examples, that in some cases it is not correct to infer constraints on the contributions from different supernovae types (Ia, II), and particularly on different sets of yields, in the absence of a complete chemical evolution model taking into account stellar lifetimes. In spite of the fact that some of these results should be well known, we believe that it is useful to discuss the meaning of abundance ratios in the light of several recent claims based upon an incorrect interpretation of observed abundance ratios. In particular, the procedure, often used in the recent literature, of directly deriving conclusions about stellar nucleosynthesis just by relating abundance ratios to yield ratios implicitly assumes the instantaneous recycling approximation. This approximation is clearly not correct when one analyses the contributions of supernovae type Ia relative to supernovae type II as functions of cosmic time. In this paper we show that the uncertainty which arises from adopting this oversimplified procedure in a variety of astrophysical objects, such as elliptical galaxies, the intracluster medium, and high redshift objects, does not allow us to draw any firm conclusion, and that the differences between abundance ratios predicted by models with the instantaneous recycling approximation and models with detailed stellar lifetimes is of the same order as the differences between different sets of yields. On the other hand, if one is interested only in establishing the global metal production (e.g. galaxies plus intracluster medium) over the lifetime of the Universe, then the adoption of simplified arguments can be justified.

The workshop programme of a new first year university astronomy subject with low capital costs incorporates diverse learning experiences: planisphere, time around the world, sundial, telescope, computer simulation, planetarium, spectroscope, poster, debate, night-time observatory trip. The practical activities, used to address specific learning objectives, emerged clearly as a major strength of the subject as evaluated by the mixed student cohort.

Though the value of hands-on learning has long been recognised by educators, it is difficult to design laboratories in astronomy classes that present realistic astrophysical techniques to undergraduate students. Unlike most other sciences, astronomy is largely observational, not experimental, and making useful observations involves expensive equipment over time scales inconvenient for pedagogy. In recent years, however, astronomy has gone almost completely digital, and the advent of large on-line databases and fast personal computers has made it possible to realistically simulate the experience of research astrophysics in the laboratory. Since 1992, Project CLEA (Contemporary Laboratory Experiences in Astronomy) has been developing computer-based exercises aimed primarily at the introductory astronomy laboratory. These exercises simulate important techniques of astronomical research using digital data and Windows-based software. Each of the nine exercises developed to date consists of software, technical guides for teachers, and student manuals for the exercises. CLEA software is used at many institutions in all the United States and over 60 countries worldwide, in a variety of settings from middle school to upper-class astronomy classes. The current design philosophy and goals of Project CLEA are discussed along with plans for future development.

This paper discusses the boundary layer and the emission spectrum from an accretion disk having a jet anchored at its inner radius, close to the black hole. We summarise our earlier work and apply it to the accretion disks of some blazars. We suggest that the ‘accretion disk with jet’ (ADJ) model could make the bridge between standard accretion disk models (suitable for quasars and FRii sources) and low-power advection dominated accretion disk models (suitable for some of the low-power BL Lacs and FRi sources).

The jet is collimated within a very narrow region close to the black hole (nozzle). In our model it is assumed that the boundary layer of the disk is the region between radius Rms — the last marginally stable circular orbit calculated for a Kerr geometry — and the radius Rjet, which gives the thickness of the ‘footring’, i.e. the base of the jet. We analyse the size of the boundary layer of the disk where the jet is fed with energy, mass, and angular momentum. As a consequence of the angular momentum extraction, the accretion disk beyond Rjet no longer has a Keplerian flow. A hot corona usually surrounds the disk, and entrainment of the corona along the flow could also be important for the energy and mass budget of the jet.

We assume that the gravitational energy available at the footring of the jet goes into the jet, and so the spectrum from the accretion disk gives a total luminosity smaller than that of a ‘standard’ accretion disk, and our ADJ model should apply for blazars with low central luminosities. Variations of the boundary layer and nozzle may account for some of the variability observed in active galactic nuclei.

A new, direct CCD acquisition and autoguiding camera is in use on the ANU 2·3 m telescope Nasmyth foci. The camera is a model AP7 manufactured by Apogee Instruments Inc. and is controlled by the MaxIm CCD camera control and image processing software developed by Diffraction Ltd. The factors influencing our choice of this new camera are discussed, and its performance, operation, and commercial control software are described. The new camera allows stellar objects as faint as B = 21·5 to be acquired on the Double Beam Spectrograph slit in 1·4″ seeing. The camera has far superior performance to the Fairchild intensified CCD cameras that it replaces. The improved acquisition and guiding permitted by this camera has already allowed several new scientific programs to begin on the telescope, including the use of aperture plates with the Double Beam Spectrograph.

All available observations of photometric standard stars obtained with the Gemini Multi-Object Spectrograph at Gemini North in the period from August 2001 to December 2003 have been used to establish the calibrations for photometry obtained with the instrument. The calibrations presented in this paper are based on significantly more photometric standard star observations than usually used by the individual users. Nightly photometric zero points as well as color terms are determined. The color terms are expected to be valid for all observations taken prior to UT 2004 November 21 at which time the Gemini North primary mirror was coated with silver instead of aluminium. While the nightly zero points are accurate to 0.02 mag or better (random errors), the accuracy of the calibrations is limited by systematic errors from so-called ‘sky concentration’, an effect seen in all focal reducer instruments. We conclude that an accuracy of 0.035 to 0.05 mag can be achieved by using calibrations derived in this paper. The color terms are strongest for very red objects, e.g. for objects with (r′ – z′) = 3.0 the resulting z′ magnitudes will be ≈0.35 mag too bright if the color term is ignored. The calibrations are of importance to the large Gemini user community with data obtained prior to UT 2004 November 21, as well as future users of achive data from this period in time.

The Taurus Tunable Filter (TTF) has now been in regular use for seven years on the Anglo–Australian Telescope (AAT). The instrument was also used for three years (1996–1999) on the William Herschel Telescope (WHT). We present a brief review of the different applications in order to illustrate the versatility of tunable filters in optical/IR spectrophotometric imaging. Tunable filters are now either planned or under development for 6–10 m class telescopes which ensures their use for years to come.

A method is presented that will enable the bivariate luminosity/surface brightness distribution of galaxies to be determined from a relatively small HI selected sample. This will be taken from the HI Parkes All Sky Survey (HIPASS). The advantages of using an HI sample in order to avoid the selection effects that are present at optical wavelengths are discussed. We are developing an algorithm to automatically extract a uniform sample of galaxies from the HIPASS data cubes and to determine the parameters of these galaxies. We have so far conducted tests involving both simulated sources injected into cubes with real noise and data from the Multibeam Deep survey. Results from these tests are encouraging.

Line broadening cross sections for the broadening of spectral lines by collisions with neutral hydrogen atoms have been tabulated by Anstee & O'Mara (1995), Barklem & O'Mara (1997) and Barklem, O'Mara & Ross (1998) for s–p, p–s, p–d, d–p, d–f and f–d transitions. To make these data more accessible to the end user, fortran code which interpolates in these tabulations has been prepared and placed on the World Wide Web. It should be easy to incorporate this code into existing spectrum synthesis programs or to use it in a stand-alone mode to compute line broadening cross sections for specific transitions. The use of the code is demonstrated by its application to two transitions of astrophysical interest.

The 2dF Galaxy Redshift Survey (2dFGRS) of 230 000 redshifts of nearby (z ~ 0.1) galaxies is now complete. It has allowed the 2dFGRS Team and others to estimate fundamental cosmological parameters and to study galaxy intrinsic properties. Here we highlight three recent key results from the survey: (a) an upper limit of about 2 eV on the total mass of the three neutrino flavours, and an intriguing reasonable fitting of the 2dFGRS power spectrum to a Mixed Dark Matter model without a Cosmological Constant but with a low Hubble constant; (b) the bimodality of the galaxy population in both spectral parameterisation and in colour; and (c) the clustering of different galaxy types and evidence for relative stochastic biasing.

The parameters of a new Australia Telescope Compact Array (ATCA) mosaic of the Large Magellanic Cloud (LMC) in the 21-cm line of neutral hydrogen are described. A preliminary peak-brightness-temperature image of the whole of the LMC, and a detailed image of the region around the supergiant shells LMC 4 and 5 is shown.

III Zw 2 shows dramatic radio outbursts roughly every five years. Here we present the light curves and VLBA observations of the latest flare with an excellent time sampling. We have detected superluminal motion with a lower limit for the apparent expansion speed of 1.25±0.09 c at 43 GHz. Spectral and spatial evolution are closely linked and the evolution of III Zw 2 in a turnover frequency vs. linear size diagram is similar to the correlation for GPS and CSS sources. Before and after this rapid expansion we observe a period of virtually no expansion. However, at 15 GHz III Zw 2 shows a constant slow expansion (∼0.6 c). The difference is qualitatively explained by optical depth effects in an ‘inflating-balloon model’, describing the evolution of radio lobes on an ultra-compact scale. The stop-and-go behaviour could be explained by a jet interacting with a molecular cloud or the molecular torus.