We describe the WFCAM Science Archive (WSA), which is the primary point of access for users of data from the wide-field infrared camera WFCAM on the United Kingdom Infrared Telescope (UKIRT), especially science catalogue products from the UKIRT Infrared Deep Sky Survey (UKIDSS). We describe the database design with emphasis on those aspects of the system that enable users to fully exploit the survey datasets in a variety of different ways. We give details of the database-driven curation applications that take data from the standard nightly pipeline-processed and calibrated files for the production of science-ready survey datasets. We describe the fundamentals of querying relational databases with a set of astronomy usage examples, and illustrate the results.Comment: 28 pages, 18 figures; accepted for publication in MNRAS (2007 November 8

Abstract. We present calculations of the spatial and spectral distribution of the radio emission from a wide WR+OB collidingwind binary system based on high-resolution hydrodynamical simulations and solutions to the radiative transfer equation. We account for both thermal and synchrotron radio emission, free-free absorption in both the unshocked stellar wind envelopes and the shocked gas, synchrotron self-absorption, and the Razin effect. To calculate the synchrotron emission several simplifying assumptions are adopted: the relativistic particle energy density is a simple fraction of the thermal particle energy density, in equipartition with the magnetic energy density, and a power-law in energy. We also assume that the magnetic field is tangled such that the resulting emission is isotropic. The applicability of these calculations to modelling radio images and spectra of colliding-wind systems is demonstrated with models of the radio emission from the wide WR+OB binary WR 147. Its synchrotron spectrum follows a power-law between 5 and 15 GHz but turns down to below this at lower and higher frequencies. We find that while free-free opacity from the circum-binary stellar winds can potentially account for the low-frequency turnover, models that also include a combination of synchrotron self-absorption and Razin effect are favoured. We argue that the highfrequency turn down is a consequence of inverse-Compton cooling. We present our resulting spectra and intensity distributions, along with simulated MERLIN observations of these intensity distributions. From these we argue that the inclination of the WR 147 system to the plane of the sky is low. We summarise by considering extensions of the current model that are important for models of the emission from closer colliding wind binaries, in particular the dramatically varying radio emission of WR 140.

Abstract. We analyse the optical spectrum of the very massive binary system WR 20a (WN6ha + WN6ha). The most prominent emission lines, Hα and He  λ 4686, display strong phase-locked profile variability. From the variations of their equivalent widths and from a tomographic analysis, we find that part of the line emission probably arises in a wind interaction region between the stars. Our analysis of the optical spectrum of WR 20a indicates a reddening of A V 6.0 mag and a distance of ∼7.9 kpc, suggesting that the star actually belongs to the open cluster Westerlund 2. The location of the system at ∼1.1 pc from the cluster core could indicate that WR 20a was gently ejected from the core via dynamical interactions. Using a non-LTE model atmosphere code, we derive the fundamental parameters of each component: T eff = 43 000 ± 2000 K, log L bol /L 6.0,Ṁ = 8.5 × 10 −6 M yr −1 (assuming a clumped wind with a volume filling factor f = 0.1). Nitrogen is enhanced in the atmospheres of the components of WR 20a, while carbon is definitely depleted. Finally, the position of the binary components in the Hertzsprung-Russell diagram suggests that they are core hydrogen burning stars in a pre-LBV stage and their current atmospheric chemical composition probably results from rotational mixing that might be enhanced in a close binary compared to a single star of same age.

INTRODUCTORY PARAGRAPHThe massive evolved Wolf-Rayet stars sometimes occur in colliding-wind binary systems in which dust plumes are formed as a result of the collision of stellar winds 1 . These structures are known to encode the parameters of the binary orbit and winds 2,3,4 . Here, we report observations of a previously undiscovered Wolf-Rayet system, 2XMM J160050.7-514245, with a spectroscopically determined wind speed of ≈ 3400 km s −1 . In the thermal infrared, the system is adorned with a prominent ≈ 12 ′′ spiral dust plume, revealed by proper motion studies to be expanding at only ≈ 570 km s −1 . As the dust and gas appear coeval, these observations are inconsistent with existing models of the dynamics of such colliding wind systems 5,6,7 . We propose that this contradiction can be resolved if the system is capable of launching extremely anisotropic winds. Near-critical stellar rotation is known to drive such winds 8,9 , suggesting this Wolf-Rayet system as a potential Galactic progenitor system for long-duration gamma-ray bursts.Corresponding author: J. R. Callingham callingham@astron.nl 2 CALLINGHAM ET AL. MAIN BODYWolf-Rayet (WR) stars represent the final stage of the evolution of the most massive stars before ending their lives as supernovae. Late-type carbon-rich WR stars with binary companions have the potential to produce spiral "Pinwheel" patterns in which dust forms at the interface between the colliding stellar winds 2,10 . As the orbital motion entangles the winds, the form of the plume encodes the primary wind and orbital parameters, forming rare and powerful laboratories for testing our understanding of the mass-loss in WR stars. For well studied Pinwheels such as WR 104 2,4 , WR 98a 3 and WR 140 11,12 , nearly complete solutions can be obtained that tightly constrain the wind speeds, wind-momentum ratio, and orbital parameters. For WR 104 and WR 140, the dust (studied by its proper motion in the thermal infrared) and the gas (the dominant wind component in the line of sight revealed by spectroscopy) have been shown to be co-moving, as expected for spherical stellar winds.Additionally, WR stars play a significant role in the chemistry and kinetic energy budget of the interstellar medium 1 , and are considered to be likely progenitors to long-duration gamma-ray bursts (GRBs) 13,14 . A key ingredient in most models for the production of long-duration GRBs is rapid rotation of the WR progenitor star 13 . For stars that have solar-like metallicity, as observed for most Galactic WR stars 15,16 , line-driven winds rapidly rob the star of angular momentum. One channel to produce near critical-rotation of the WR star before undergoing a core-collapse supernova is through binary interaction 17 . Unfortunately debates over the role of rotation remain largely in the domain of theory as it has proven extremely difficult to place any observational constraints on the rotation of WR stars. Because WR spectra are generally formed in their extended dense winds 18 , obtaining rotational velocity from fitting t...

Abstract.We analyse spectroscopic observations of WR 20a revealing that this star is a massive early-type binary system with a most probable orbital period of ∼3.675 days. Our spectra indicate that both components are most likely of WN6ha or O3If * /WN6ha spectral type. The orbital solution for a period of 3.675 days yields extremely large minimum masses of 70.7 ± 4.0 and 68.8± 3.8 M for the two stars. These properties make WR 20a a cornerstone system for the study of massive star evolution.

We present high‐resolution infrared (2–18 μm) images of the archetypal periodic dust‐making Wolf–Rayet binary system WR 140 (HD 193793) taken between 2001 and 2005, and multi‐colour (J–[19.5]) photometry observed between 1989 and 2001. The images resolve the dust cloud formed by WR 140 in 2001, allowing us to track its expansion and cooling, while the photometry allows tracking the average temperature and total mass of the dust. The combination of the two data sets constrains the optical properties of the dust, and suggests that they differ from those of the dust made by the WC9 dust‐makers, including the classical ‘pinwheel’, WR 104. The photometry of individual dust emission features shows them to be significantly redder in (nbL′–[3.99]), but bluer in ([7.9]–[12.5]), than the binary, as expected from the spectra of heated dust and the stellar wind of a Wolf–Rayet star. The most persistent dust features, two concentrations at the ends of a ‘bar’ of emission to the south of the star, were observed to move with constant proper motions of 324 ± 8 and 243 ± 7 mas yr−1. Longer wavelength (4.68 and 12.5 μm) images show dust emission from the corresponding features from the previous (1993) periastron passage and dust formation episode, showing that the dust expanded freely in a low‐density void for over a decade, with dust features repeating from one cycle to the next. A third persistent dust concentration to the east of the binary (the ‘arm’) was found to have a proper motion ∼320 mas yr−1, and a dust mass about one‐quarter that of the ‘bar’. Extrapolation of the motions of the concentrations back to the binary suggests that the eastern ‘arm’ began expansion four to five months earlier than those in the southern ‘bar’, consistent with the projected rotation of the binary axis and wind‐collision region (WCR) on the sky. A comparison of model dust images and the observations constrains the intervals when the WCR was producing sufficiently compressed wind for dust nucleation in the WCR, and suggests that the distribution of this material was not uniform about the axis of the WCR, but more abundant in the following edge in the orbital plane.

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The Wolf-Rayet WC7+O4-5 binary WR 140 went through the periastron passage of its 8 yr eccentric binary orbit in early 2001 as the two stars made their closest approach. Both stars have powerful supersonic stellar winds that crash into each other between the stars to produce X-rays. Chandra grating observations were made when the X-rays were at their peak, making WR 140 the brightest hot-star X-ray source in the sky and giving the opportunity to study the velocity profiles of lines, all of which were resolved and blueshifted before periastron. In the general context of shock physics, the measurements constrain the flow of hot gas and where different ions were made. The brightness of lines relative to the strong continuum in conjunction with plasma models gives interim abundance estimates for eight different elements in WC-type material including an Ne/S ratio in good agreement with earlier long-wavelength measurements. The lower velocity widths of cool ions imply a plasma that was not in equilibrium, probably due to the collisionless nature of the shock transitions and the slow character of both the postshock energy exchange between ions and electrons and subsequent ionization. Electron heat conduction into fast-moving preshock gas was absent, probably suppressed by the magnetic field involved in WR 140's synchrotron emission. After periastron, the spectrum was weaker due mainly to absorption by cool Wolf-Rayet star material.