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Climatic conditions and cultural practices in the sub-tropical and tropical high-rainfall regions in which sugarcane is grown in Australia are conducive to rapid carbon and nitrogen cycling. Previous research has identified substantial exchanges of methane (CH4) and nitrous oxide (N2O) between sugarcane soils and the atmosphere. However, that research has been mostly short-term. This paper describes recent work aimed at quantifying exchanges of CH4 and N2O from fertilised sugarcane soils over whole growing seasons. Micrometeorological and chamber techniques provided continuous measurements of gas emissions in whole-of-season studies in a burnt-cane crop on an acid sulfate soil (ASS) that was fertilised with 160kg nitrogen (N)ha-1 as urea in the south of the sugarcane belt (Site 1), and in a crop on a more representative trash-blanketed soil fertilised with 150kg urea-Nha-1 in the north (Site 2). Site 1 was a strong source of CH4 with a seasonal emission (over 342 days) of 19.9kg CH4ha-1. That rate corresponds to 0.5-5% of those expected from rice and wetlands. The many drains in the region appear to be the main source. The net annual emission of CH4 at Site 2 over 292 days was essentially zero, which contradicts predictions that trash-blankets on the soil are net CH4 sinks. Emissions of N2O from the ASS at Site 1 were extraordinarily large and prolonged, totalling 72.1kgN2Oha-1 (45.9kgNha-1) and persisting at substantial rates for 5 months. The high porosity and frequent wetting with consequent high water filled pore space and the high carbon content of the soil appear to be important drivers of N2O production. At Site 2, emissions were much smaller, totalling 7.4kgN2Oha-1 (4.7kgNha-1), most of which was emitted in less than 3 months. The emission factors for N2O (the proportion of fertiliser nitrogen emitted as N2O-N) were 21% at Site 1 and 2.8% at Site 2. Both factors exceed the default national inventory value of 1.25%. Calculations suggest that annual N2O produc

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Re-examination of extensive photometric data of TV Col reveals evidence for a permanent positive superhump. Its period (6.4 h) is 16 percent longer than the orbital period and obeys the well known relation between superhump period excess and binary period. At 5.5-h, TV Col has an orbital period longer than any known superhumping cataclysmic variable and, therefore, a mass ratio which might be outside the range at which superhumps can occur according to the current theory. We suggest several solutions for this problem., Comment: 5 pages, 2 eps. figures, Latex, proceedings of `Evolution of Binary and Multiple Star Systems', a Meeting in Celebration of Peter Eggleton's 60th Birthday, Bormio, Italy, ASP Conference Series, eds. Ph. Podsiadlowski et al., ASP, San Francisco

We take a critical look at the lithium depletion boundary (LDB) technique that has recently been used to derive the ages of open clusters. We identify the sources of experimental and systematic error and show that the probable errors are larger by approximately a factor two than presently claimed in the literature. We then use the Pleiades LDB age and photometry in combination with evolutionary models to define empirical colour-T_eff relations that can be applied to younger clusters. We find that these relationships DO NOT produce model isochrones that match the younger cluster data. We propose that this is due either to systematic problems in the evolutionary models or an age (gravity) sensitivity in the colour-T_eff relation which is not present in published atmospheric models., Comment: 6 pages, to appear in - From Darkness to Light, ASP Conference Series, eds. T. Montmerle and Ph. Andre

Archival data on permanent superhump systems are compiled to test the thermal stability of their accretion discs. We find that their discs are almost certainly thermally stable as expected. This result confirms Osaki's suggestion (1996) that permanent superhump systems form a new subclass of cataclysmic variables (CVs), with relatively short orbital periods and high mass transfer rates. We note that if the high accretion rates estimated in permanent superhump systems represent their mean secular values, then their mass transfer rates cannot be explained by gravitational radiation, therefore, either magnetic braking should be extrapolated to systems below the period gap or they must have mass transfer cycles. Alternatively, a new mechanism that removes angular momentum from CVs below the gap should be invoked. We suggest applying the nova cycle scenarios offered for systems above the period gap to the short orbital period CVs. Permanent superhumps have been observed in the two non-magnetic ex-novae with binary periods below the gap. Their post-nova magnitudes are brighter than their pre-outburst values. In one case (V1974 Cyg) it has been demonstrated that the pre-nova should have been a regular SU UMa system. Thus it is the first nova whose accretion disc was observed to change its thermal stability. If the superhumps in this system indicate persistent high mass transfer rates rather than a temporary change induced by irradiation from the hot post-nova white dwarf, it is the first direct evidence for mass transfer cycles in CVs. The proposed cycles are driven by the nova eruption., Comment: 7 pages, 2 eps. figures, Latex, accepted for publication in MNRAS

We present 53 simultaneous photometric (I band) and spectroscopic (6900-9500 Angstroms) observations of J0422+32, taken during December 1997. From these we determine that J0422+32 was in its lowest state yet observed, at I=20.44+/-0.08. Using relative spectrophotometry, we show that it is possible to correct very accurately for telluric absorption. Following this, we use the TiO bands at 7055 Angstroms and 7589 Angstroms for a radial velocity study and thereby obtain a semi-amplitude of 378+/-16kms-1, which yields f(M)=1.191+/-0.021M_solar and q=9.0+2.2-2.7, consistent with previous observations. We further demonstrate that this little explored method is very powerful for such systems. We also determine a new orbital ephemeris of HJD=2450274.4156+/-0.0009 + 0.2121600+/-0.0000002E. We see some evidence for an ellipsoidal modulation, from which we determine the orbital inclination of J0422+32 to be less than 45 degrees. We therefore calculate a minimum mass for the primary of 2.22M_solar, consistent with a black hole, but not necessarily the super-massive one proposed by Beekman et al (1997). We obtain an M4-5 spectral type for the secondary star and determine that the secondary contributes 38+/-2% of the flux that we observe from J0422+32 over the range 6950-8400 Angstroms. From this we calculate the distance to the system to be 1.39+/-0.15kpc., Comment: (1) Department of Physics, Keele University, Keele, Staffordshire, ST5 5BG (2) Department of Astrophysics, Nuclear Physics Laboratory, Keble Road, Oxfo rd, OX1 3RH Accepted, to appear in MNRAS 8 pages, 5 figures

We present red spectra in the region 7000-8300A of the eclipsing dwarf nova IP Peg, with simultaneous narrow-band photometry centered at 7322A. We show that by placing a second star on the slit we can correct for the telluric absorption bands which have hitherto made the TiO features from the secondary star unusable. We use these TiO features to carry out a radial velocity study of the secondary star, and find this gives an improvement in signal-to-noise of a factor two compared with using the Na{I} doublet. In contrast with previous results, we find no apparent ellipticity in the radial velocity curve. As a result we revise the semi-amplitude to 331.3+/-5.8km/s, and thus the primary and secondary star masses to 1.05Mo and 0.33Mo respectively. Although this is the lowest mass yet derived for the secondary star, it is still over-massive for its observed spectral type. However, the revised mass and radius bring IP Peg into line with other CVs in the mass-radius-period relationships. By fitting the phase resolved spectra around the TiO bands to a mean spectrum, we attempt to isolate the lightcurve of the secondary star. The resulting light curve has marked deviations from the expected ellipsoidal shape. The largest difference is at phase 0.5, and can be explained as an eclipse of the secondary star by the disc, indicating that the disc is optically thick when viewed at high inclination angles., Comment: Accepted for publication in MNRAS. 10 pages and 10 figures

We present the 45-yr record of EX Hya's lightcurve and discuss the characteristics of its 15 observed outbursts. We then concentrate on the 1998 outburst, reporting the first outburst X-ray observations. We discover an X-ray beat-cycle modulation, indicating that an enhanced accretion stream couples directly with the magnetosphere in outburst, confirming our previous prediction. Optical eclipse profiles late in outburst show that the visible light is dominated by an enhanced mass-transfer stream overflowing the accretion disc. We are uncertain whether the enhanced mass transfer is triggered by a disc instability, or by some other cause. While in outburst, EX Hya shows some of the characteristics of SW Sex stars., Comment: To appear in MNRAS (8 pages; 9 figs)

We report the serendipitous discovery of a population of low mass, pre-main sequence stars (PMS) in the direction of the Wolf-Rayet/O-star binary system gamma^{2} Vel and the Vela OB2 association. We argue that gamma^{2} Vel and the low mass stars are truly associated, are approximately coeval and that both are at distances between 360-490 pc, disagreeing at the 2 sigma level with the recent Hipparcos parallax of gamma^{2} Vel, but consistent with older distance estimates. Our results clearly have implications for the physical parameters of the gamma^{2} Vel system, but also offer an exciting opportunity to investigate the influence of high mass stars on the mass function and circumstellar disc lifetimes of their lower mass PMS siblings., Comment: Monthly Notices of the Royal Astronomical Society, Letters - in press