Luminous water maser emission in the 616–523 line at 22GHz has been detected from two dozen galaxies. In all cases the emission is confined to the nucleus and has been found only in AGN, in particular, in Type 2 Seyferts and LINERs. I argue that most of the observed megamaser sources are powered by X-ray irradiation of dense gas by the central engine. After briefly reviewing the physics of these X-Ray Dissociation Regions, I discuss in detail the observations of the maser disk in NGC 4258, its implications, and compare alternative models for the maser emission. I then discuss the observations of the other sources that have been imaged with VLBI to date, and how they do or do not fit into the framework of a thin, rotating disk, as in NGC 4258. Finally, I briefly discuss future prospects, especially the possibility of detecting other water maser transitions.

Small bodies of 100–500 m diameter can cause significant damage on impact with the Earth. Such objects are difficult to detect and track because they are intrinsically faint over most of their orbit. We failed to detect one such lost and potentially hazardous minor planet, 1998 OX4, during two observing sessions in 2001, January. The positions searched were those calculated by Milani et al. (2000) with their Virtual Impactors method. Using some simple assumptions we estimate the probability that we failed to detect 1998 OX4 due to it being obscured by objects in the field of our observations is <2 × 10−7. If the assumptions in the Virtual Impactor model are valid we conclude that an impact with 1998 OX4 is unlikely in 2014, January. Furthermore, given the relatively large area we searched it is also unlikely that this minor planet will have a very close encounter with Earth in 2014.

In this paper we present a new method for obtaining the optical wavelength-dependent reddening function of planetary nebulae (PN), using the nebular and stellar continuum. The data used was a spectrum of NGC 6302 obtained using the Double Beam Spectrograph on the 2.3 m telescope at Siding Springs Observatory over three nights. This resulted in a spectrum covering a wavelength range 3300–8600 Å with a large dynamical range and a mean signal to noise of >102 Å−1 in the nebular continuum. With such a high S/N the continuum can be accurately compared with a theoretical model of nebular plus stellar continuum. The nebular electron temperature and density used in the model are determined using ratios of prominent emission lines. The reddening function can then be obtained from the ratio of the theoretical and the observed continuum. In the case of NGC 6302, it is known that much of the reddening arises from dust within or around the nebula, so that any differences between the measured reddening law and the 'standard' interstellar reddening law will reflect differences in the nebular grain size distribution or composition. We find that for NGC 6302, the visible to IR extinction law is indistinguishable from 'standard' interstellar reddening, but that the UV extinction curve is much steeper than normal, suggesting that more small dust grains had been ejected into the nebula by the PN central star. We have detected the continuum from the central star and determined its Zanstra temperature to be of order 150,000 K. Finally, using the extinction law that we have determined, we present a complete dereddened line list of nearly 600 emission lines, and report on the detection of the He(2–10) and He(2–8) Raman features at λ4331 Å and λ4852 Å, and the detection of Raman scattered O VI features at λ6830 Å and λ7087 Å. We believe this to be the first detection of this process in a PN.

We present the results of a program to develop techniques that enable high-resolution photometric measurements using modest research instruments available to small colleges, and then demonstrate those techniques in a pilot photometric project.

Using a 25 cm Schmidt–Cassegrain telescope and SBIG ST7E CCD camera, we develop techniques that enabled milli-magnitude photometric resolution. The pilot project studied five transits of the recently discovered gas giant planet orbiting HD 209458. We measured a flux drop of 1.46 ± 0.17% during the transit which corresponds to a planetary diameter of 1.39 ± 0.14 RJup, a transit period of 2h 48min ± 21min, and planet orbital inclination of 87.6 ± 1.3°. We determined the orbital period as 3.5234 ± 0.0026 days. These results agree well with other studies which used professional grade research instruments. We suggest a number of other challenging photometric research areas suitable for graduate and undergraduate investigation using equipment common to many small colleges.

Swinburne Astronomy Online (SAO) is an online graduate program in astronomy intended particularly for amateur astronomers, science communicators and educators. SAO emphasises the development of conceptual understanding and good communication skills in astronomy. The use of asynchronous discussion forums is a central feature of SAO. These 'online tutorials' were introduced partly with the intention of breaking down the isolation of distance education, but mainly to provide a venue where students could deepen their conceptual understanding of astronomy and hone their science communication skills while discussing course material with other students and instructors.

In this project aspects of the use of discussion forums in SAO were investigated, with comparisons made between average marks awarded for discussion forum contributions and those awarded for other assessment tasks, plus analysis of the rate at which students post to the forums, and an investigation of whether gender makes a significant difference to participation rate and assessment results. Responses by students to surveys that probe their ability to express themselves and communicate with classmates in this online form of distance education are discussed. Finally, possible implications for the use of discussion forums as a supplement to face-to-face teaching in astronomy are explored.

We present a catalogue of the 322 damped Lyman alpha absorbers taken from the literature. All damped Lyman alpha absorbers are included, with no selection on redshift or quasar magnitude. Of these, 123 are candidates and await confirmation using high resolution spectroscopy. For all 322 objects we catalogue the radio properties of the background quasars, where known. Around 60 quasars have radio flux densities above 0.1 Jy and approximately half of these have optical magnitudes brighter than V = 18. This compilation should prove useful in several areas of extragalactic/cosmological research.

A new astronomical window into the southern skies has been opened with the high-frequency upgrade to the Australia Telescope Compact Array (ATCA), which allows radio-interferometric mapping of sources at wavelengths as short as 3 mm. In anticipation of the upgrade's completion, a two-day workshop was held at the University of Melbourne in November 2001. The workshop covered a diverse range of fields, tied together by a common theme of identifying key areas where ATCA observations can have an impact. More than half of the talks were concerned with molecular clouds and star formation, with the remainder covering topics such as molecular gas in the Galactic Centre, Seyfert nuclei, and high-redshift objects. Some early results from the 3 and 12 mm prototype systems were also presented. In consultation with the speakers, we are presenting in this article a summary of the talks. The original slides are available from the ATNF website.

The relationship between observed variability time and emission region geometry is explored for the case of emission by relativistic jets.The approximate formula for the jet-frame size of the emission region, R′ = DcΔtobs, is shown to lead to large systematic errors when used together with observed luminosity and assumed or estimated Doppler factor D to estimate the jet-frame photon energy density. These results have implications for AGN models in which low-energy photons are targets for interaction of high energy particles and photons, e.g. synchrotron-self Compton models and hadronic blazar models, as well as models of intraday variable sources in which the photon energy density imposes a brightness temperature limit through Compton scattering.

The actual relationship between emission region geometry and observed variability is discussed for a variety of geometries including cylinders, spheroids, bent, helical and conical jet structures, and intrinsic variability models including shock excitation. The effects of time delays due to finite particle acceleration and radiation timescales are also discussed.

When a star with a mass of one to a few solar masses enters the red giant stage of its evolution, the radius of its atmosphere reaches several astronomical units. Pulsational instability is typical for this stage. Most stars become Mira-type or semiregular variables with light cycles of a few hundred days. Red giants lose mass at a rate M = 10−7−10−5M⊙ yr−1. Extensive gas–dust circumstellar envelopes form. These envelopes contain various molecular species. Some of these molecules (OH, H2O, SiO, HCN) manifest themselves in maser radio emission. Data on the H2O maser variability and its connection with the stellar brightness variations are discussed. In the H2O line circumstellar masers can be divided into ‘stable’ (showing persistent emission — R Aql, U Her, S CrB, X Hya) and ‘transient’ (appearing in the H2O line once per 10–15 stellar light cycles — R Leo, R Cas, U Aur). Physical mechanisms of the maser variability are discussed. The most probable process explaining the observed visual–H2O correlation is the influence of shock waves on the masing region. Usually it is assumed that shocks in Mira atmospheres are driven by stellar pulsations. Here an alternative explanation is proposed. If a star during its main sequence life possessed a planetary system, similar to the solar system, the planets will be embedded in a rather dense and hot medium. Effects of a planet revolving around a red giant at a short distance (inside its circumstellar envelope) are discussed. A shock produced by the supersonic motion of a planet can account for the correlated variability of the Hα line emission and H2O maser. If the planetary orbit is highly eccentric, then the connected Hα–H2O flare episodes may be explained by the periastron passage of the planet. New tasks for the upgraded ATCA are discussed.

We present results from a spectral line survey of the young stellar object IRAS 17470-2853, undertaken to examine chemical changes during the evolution from hot molecular cores to ultracompact HII regions. Observations were carried out with the Mopra 22 m radio telescope in the frequency range from 86.1 to 92.1 GHz. A total of 21 lines from 9 molecules were detected. Except for CH3CN they are all simple molecules. We compare the results to the ultracompact HII region G34.3+0.15, where spectral line surveys in the frequency range 80–115 GHz and 330–360 GHz have been performed. While the molecular lines detected are similar, their widths and intensities are somewhat narrower and lower, respectively, in IRAS 17470-2853. The typical line width of ˜5 km s−1 indicates relatively quiet or quasi-thermal emission. On the other hand, a significant difference in TA* (HNC)/TA*(HCN) has been found: 0.8 for IRAS 17470-2853 compared to 2.6 for G34.3+0.15. The broad line width of SiO (υ=0, J=2–1), ˜9 km s−1, suggests that IRAS 17470-2853 is experiencing a shock generated by the embedded object. Column densities, or lower limits to them, are derived for observed molecules.

We present new evolutionary sequences for low and intermediate mass stars (1−6M⊙) for three different metallicities, Z = 0.02, 0.008, and 0.004. We evolve the models from the pre-main sequence to the thermally-pulsing asymptotic giant branch phase. We have two sequences of models for each mass, one which includes mass loss and one without mass loss. Typically 20 or more pulses have been followed for each model, allowing us to calculate the third dredge-up parameter for each case. Using the results from this large and homogeneous set of models, we present an approximate fit for the core mass at the first thermal pulse, Mc1, as well as for the third dredge-up efficiency parameter, λ, and the core mass at the first dredge-up episode, Mcmin, as a function of metallicity and total mass. We also examine the effect of a reduced envelope mass on the value of λ.

This paper presents the results of a multiwavelength observational study of the active young F-type star HR 1817. The star was monitored at 4.80 and 8.64 GHz over 2 × 12 h allocations with the Australia Telescope Compact Array on 8 and 9 December, 2000. The Anglo-Australian Telescope was used for simultaneous optical spectropolarimetry during a 2 h period on 9 December.

The low levels of observed radio emission have characteristics that are similar to those seen in other active stars, and a gyrosynchrotron mechanism is proposed to explain them; this is supported by the relatively low fractions of circular polarisation measured in HR 1817.

Comparison of the emissions from 4.80 and 8.64 GHz shows a very strong cross-correlation peak, indicative of a common origin, although the shift of this peak indicates that 8.64 GHz variations tend to precede those at 4.80 GHz by, typically, ˜20 min.

The optical spectropolarimetry reveals polarisation signals characteristic of surface magnetic fields, with profile changes indicating a complex dynamo-type magnetic topology is present on the star. This result makes HR 1817 the star with the earliest spectral type on which dynamo magnetic fields have been detected directly up to now.