Molecular hydrogen emission from discs in the η Chamaeleontis cluster

Discs in the 6 Myr old cluster η Chamaeleontis were searched for emission from hot H₂. Around the M3 star ECHA J0843.3−7905, we detect circumstellar gas orbiting at ∼2 au. If the gas is ultraviolet excited, the ro-vibrational line traces a hot gas layer supported by a disc of mass  ∼0.03 M_⊙  , similar to the minimum mass solar nebula. Such a gas reservoir at 6 Myr would promote the formation and the inwards migration of gas giant planets.     

First XMM-Newton observations of strongly magnetic cataclysmic variables – II. Timing studies of DP Leo and WW Hor

XMM-Newton was used to observe two eclipsing, magnetic cataclysmic variables, DP Leo and WW Hor, continuously for three orbital cycles each. Both systems were in an intermediate state of accretion. For WW Hor we also obtained optical light curves with the XMM-Newton Optical Monitor and from ground-based observations. Our analysis of the X-ray and optical light curves allows us to constrain physical and geometrical parameters of the accretion regions and derive orbital parameters and eclipse ephemerides of the systems. For WW Hor we directly measure horizontal and vertical temperature variations in the accretion column. From comparisons with previous observations we find that changes in the accretion spot longitude are correlated with the accretion rate. For DP Leo the shape of the hard X-ray light curve is not as expected for optically thin emission, showing the importance of optical depth effects in the post-shock region. We find that the spin period of the white dwarf is slightly shorter than the orbital period and that the orbital period is decreasing faster than expected for energy loss by gravitational radiation alone.     

XMM–Newton observations of the complex spin pulse of the intermediate polar PQ Geminorum

The intermediate polar PQ Geminorum shows a complex pulsation, caused by a spinning white dwarf, which varies markedly with wavelength. We report XMM–Newton observations, including the soft and hard X-ray bands and the first ultraviolet light curves of this star. We update the ephemeris for PQ Gem allowing us to align these data with a compilation of light curves from the optical to the X-ray. Building on work by previous authors, we show how a model in which accretion flows along skewed field lines, viewed at the correct inclination, can explain the major features of the light curves in all bands. We discuss how the skew of the field lines relates to the spinning down of the white dwarf rotation.     

XMM–Newton observations of the eclipsing polar V2301 Oph

We present XMM–Newton observations of the eclipsing polar V2301 Oph which cover nearly 2.5 binary orbital cycles and two eclipses. This polar is believed to have the lowest magnetic field strength (7 MG) of any known polar. We find evidence for structure in the X-ray eclipse profile which shows a 'standstill' feature lasting  26 ± 4  s. This allows us to place an upper limit on the mass of the white dwarf of  ∼1.2 M_⊙  . We find no evidence for quasi-periodic oscillations (QPOs) in the frequency range 0.02–10 Hz. This coupled with the absence of QPOs in RXTE data suggests that, if present, any oscillations in the shock front have a minimal effect on the resultant X-ray flux. We find no evidence for a distinct soft X-ray component in its spectrum – it therefore joins another seven systems which do not show this component. We suggest that those systems which are asynchronous, have low mass-transfer rates or have accretion occurring over a relatively large fraction of the white dwarf are more likely to show this effect. We find that the specific mass-transfer rate has to be close to 0.1 g cm⁻² s⁻¹ to predict masses which are consistent with that derived from our eclipse analysis. This may be due to the fact that the low magnetic field strength allows accretion to take place along a wide range of azimuth.     

Imaging and integral-field spectroscopy of shocked H2 around G25.65+1.05

The results of B -band CCD imaging linear polarimetry obtained for stars from the Hipparcos catalogue are used to re-examine the distribution of the local interstellar medium towards the IRAS 100-μm emission void in the Lupus dark clouds. The analysis of the obtained parallax–polarization diagram assigns to the dark cloud Lupus 1 a distance between 130 and 150 pc and assures the existence of a low column density region coincident with the observed infrared void. Moreover, there are clear indications of the existence of absorbing material at distances closer than 60–100 pc, which may be associated with the interface boundary between the Local Bubble and its neighbourhood Loop I superbubble.     

The DH ratio in the atmosphere of Uranus: Detection of the R5(1) line of HD

Observations of Uranus during the 1975, 1976, and 1978 apparitions reveal a weak absorption at the wavelength of the R₅(1) line of HD with equivalent width $\text{1.0 ± 0.4}\text{m}\text{A}\text{?}$. The $\text{D}\text{H}$ ratio in Uranus' atmosphere implied by this line and other published spectra is (4.8 ± 1.5) × 10^?5, and may not be significantly different from that in the atmospheres of Jupiter and Saturn. In addition, the spectra exhibit two weak absorption at $\text{6044.76 ± 0.02}\text{and}\text{6045.54 ± 0.02}\text{A}\text{?}$ which we were unable to identify. No trace of absorption is visible near these wavelengths or near the HD wavelength in a laboratory spectrum of 4.92 km-am CH₄ which we obtained in an attempt to identify these absorption features and to verify that the HD feature does not arise from CH₄.     

RApid Temporal Survey (RATS) – I. Overview and first results

We present the aim and first results of the RApid Temporal Survey (RATS) made using the Wide Field Camera on the Isaac Newton Telescope. Our initial survey covers 3 square degrees, reaches a depth of   V ∼ 22.5  and is sensitive to variations on time-scales as short as 2 min: this is a new parameter space. Each field was observed for over 2 h in white light, with 12 fields being observed in total. Our initial analysis finds 45 targets which show significant variations. Around half of these systems show quasi-sinusoidal variations: we believe they are contact or short period binaries. We find four systems which show variations on a time-scale less than 1 h. The shortest period system has a period of 374 s. We find two systems which show a total eclipse. Further photometric and spectroscopic observations are required to fully identify the nature of these systems. We outline our future plans and objectives.