We present the Macquarie/AAO/Strasbourg Hα Planetary Nebula Catalogue (MASH) of over 900 true, likely and possible new Galactic planetary nebulae (PNe) discovered from the AAO/UKST Hα survey of the southern Galactic plane. The combination of depth, resolution, uniformity and areal coverage of the Hα survey has opened up a hitherto unexplored region of parameter space permitting the detection of this significant new PN sample. Away from the Galactic bulge the new PNe are typically more evolved, of larger angular extent, of lower surface brightness and more obscured (i.e. extinguished) than those in most previous surveys. We have also doubled the number of PNe in the Galactic bulge itself and although most are compact, we have also found more evolved examples. The MASH catalogue represents the culmination of a seven-year programme of identification and confirmatory spectroscopy.A key strength is that the entire sample has been derived from the same, uniform observational data. The 60 per cent increase in known Galactic PNe represents the largest ever incremental sample of such discoveries and will have a significant impact on many aspects of PN research. This is especially important for studies at the faint end of the PN luminosity function which was previously poorly represented.

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The Molonglo Observatory Synthesis Telescope is equipped with a transient event monitoring system which operates during normal synthesis observations. The device is designed to respond to impulsive signals which occur within the passband (843.0 ± 1.5 MHz) with time scales between 0.001 ms and 800 ms. The multiple beam facility of the telescope provides some discrimination against local interference. An upper limit of 1.7 × 10−2 events s−1 sr−1 has been placed on celestial events with durations between 1 ms and 25 ms and energy density ≥ 10−28 J m−2 Hz−1. The monitoring system has been recently reconfigured to improve the recognition and rejection of impulsive signals of non-celestial origin.

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OH masers at 1720 MHz have proven to be excellent indicators of interactions between supernova remnants and molecular clouds. OH excitation calculations suggest that the 6049 MHz OH maser line is excited for higher column densities than for the 1720 MHz line. Previous observations and modelling of 1612, 1665 and 1667 MHz OH absorption and 1720 MHz OH masers indicated that the column densities in some supernova remnants, ~1e17 cm^-2, may be high enough for 6049 MHz OH masers to exist. It is therefore a potentially valuable indicator of remnant-cloud interaction. We present excitation calculations predicting the formation of 6049 MHz OH masers and results of a survey using the Parkes Methanol Multibeam receiver for 6049, 6035 and 6030 MHz OH masers towards 35 supernova remnants, a star-forming region and 4 fields in the Large and Small Magellanic Clouds. Two new sites of 6035 and 6030 MHz OH maser emission associated with star-forming regions have been discovered, but no 6049 MHz masers were detected to a brightness temperature limit of ~0.3-0.6 K, even though modelling of the OH excitation suggests that maser emission should have been detected. Our upper-limits indicate that the OH column density for a typical remnant is less than 1e16.4 cm^-2, which conflicts with observed and modelled column densities. One possible explanation is that 6049 MHz OH masers may be more sensitive to velocity coherence than 1720 MHz OH masers under some conditions.Comment: 11 pages, 5 figures, mn2e.cls. Submitted to MNRAS Apr 2008. Accepted for publication in MNRAS 2008 July 15. Minor changes in the accepted version. LaTex2

The single G8V active chromosphere star HD36705 (AB Dor) was observed at 8.4 GHz with the Parkes 64 m telescope during three observing sessions involving a total of 21 days in the interval 1985 December to 1986 February. Subsequent photometric observations were made of the star with the 0.25 m and 0.45 m telescopes of the Monash Observatory in 1986 March-April. Two strong radio flares, each lasting three days, were detected; they yielded peak radio powers of / ) !.4«4xlO'WHz"', comparable with the microwave power emitted by the RS CVn binaries. Significant circular polarization of 13% left-hand was measured on only one of the six active days. The 8.4 GHz flux density showed smooth variation over an interval of several hours, consistent with the flare source being partly occulted by the stellar disk as the star rotated. When all the radio data was phase-binned using the known rotation period of 0.514 day we found two radio maxima corresponding to radio sources at stellar longitudes ~180° apart. The subsequent photometric data showed intensity variations that were consistent with the starspots at the same approximate longitudes. We thus interpret our radio curve as showing the presence of comparatively small (<0.5 D t ) radio sources in the corona above the star spots. The upper limit to source diameter gives a peak brightness temperature ^2xl0 1 0 K, which can be achieved by gyro-synchrotron emission only if the source is optically thick and the electrons, with average energy ~ 2 MeV, have a hard energy spectrum. The observed radiation can be due only to very high harmonics of the gyro-frequency, leading to an estimate for the magnetic field strength of -30G.