P. M. Williams

The SuperCOSMOS Sky Survey – I. Introduction and description

In this, the first in a series of three papers concerning the SuperCOSMOS Sky Survey (SSS), we give an introduction and user guide to the survey programme. We briefly describe other wide-field surveys and compare them with our own. We give examples of the data, and make a comparison of the accuracies of the various image parameters available with those from the other surveys providing similar data; we show that the SSS data base and interface offer advantages over these surveys. Some science applications of the data are also described and some limitations discussed. The series of three papers constitutes a comprehensive description and user guide for the SSS.

The WFCAM Science Archive

We describe the WFCAM Science Archive, 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. We describe the database design with emphasis on those aspects of the system that enable users to fully exploit the survey data sets 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 data sets. We describe the fundamentals of querying relational databases with a set of astronomy usage examples, and illustrate the results.

WR 20a: A massive cornerstone binary system comprising two extreme early-type stars

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 Mfor the two stars. These properties make WR 20a a cornerstone system for the study of massive star evolution.

The spectrum of the very massive binary system WR20a (WN6ha + WN6ha): Fundamental parameters and wind interactions

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 AV � 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: Teff = 43 000 ± 2000 K, log Lbol/L� � 6.0, u M = 8.5 × 10 −6 Myr −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 as ingle star of same age.

VISTA data flow system: overview

Data from the two IR survey cameras WFCAM (at UKIRT in the northern hemisphere) and VISTA (at ESO in the southern hemisphere) can arrive at rates approaching 1.4 TB/night for of order 10 years. Handling the data rates on a nightly basis, and the volumes of survey data accumulated over time each present new challenges. The approach adopted by the UKs VISTA Data Flow System (for WFCAM & VISTA data) is outlined, emphasizing how the design will meet the end-to-end requirements of the system, from on-site monitoring of the quality of the data acquired, removal of instrumental artefacts, astrometric and photometric calibration, to accessibility of curated and user-specified data products in the context of the Virtual Observatory. Accompanying papers by Irwin et al and Hambly et al detail the design of the pipeline and science archive aspects of the project.

Episodic dust formation by HD 192641 (WR 137) – II

Observations of the dust and gas around embedded stellar clusters reveal some of the processes involved in their formation and evolution. Large scale mass infall with rates dM/dt=4e-4 solar masses/year is found to be disrupted on small scales by protostellar outflows. Observations of the size and velocity dispersion of clusters suggest that protostellar migration from their birthplace begins at very early times and is a potentially useful evolutionary indicator.

Multi-frequency variations of the Wolf-Rayet system HD 193793 (WC7pd + O4-5). III. IUE observations.

The colliding-wind binary system WR140 (HD193793, WC7pd+O4-5, P=7.94 yr) was monitored in the ultraviolet by IUE from 1979 to 1994 in 35 short-wavelength high-resolution spectra. An absorption-line radial-velocity solution is obtained from the photospheric lines of the O component, by comparison with a single O star. The resulting orbital parameters, e=0.87 +/- 0.05, w=31 degrees +/- 9 degrees and Ko star=25 +/- 15 km s(-1), confirm the large eccentricity of the orbit, within the uncertainties of previous optical studies. This brings the weighted mean UV-optical eccentricity to e=0.85 +/- 0.04. Occultation of the O-star light by the WC wind and the WC+O colliding-wind region results into orbital modulation of the P-Cygni profiles of the C II, CIV and Si IV resonance lines. Near periastron passage, the absorption troughs of those resonance-line profiles increase abruptly in strength and width, followed by a gradual decrease. In particular, near periastron the blue black-edges of the P-Cygni absorption troughs shift to larger out ow velocities. We discuss that the apparently larger wind velocity and velocity dispersion observed at periastron could be explained by four phenomena: (i) geometrical resonance-line eclipse effects being the main cause of the observed UV spectral variability, enhanced by sightline crossing of the turbulent wind-wind collision zone; (ii) the possibility of an orbital-plane enhanced WC7 stellar wind; (iii) possible common-envelope acceleration by the combined WC and O stellar radiation fields; and (iv) possible enhanced radiatively driven mass loss due to tidal stresses, focused along the orbiting line of centers.

WSRT 1.4 and 5-GHz light curves for WR 147 (AS 431, WN8(h)+OB)

The results of more than 8-yr monitoring (1988-1997) of the Wolf-Rayet binary WR 147 (WN8(h)-OB) with the Westerbork Synthesis Radio Telescope (WSRT) are presented. When the strong winds of the Wolf-Rayet (WR) and OB binary components collide. they produce non-thermal excess radiation in the region where the two winds interact. The binary system, monitored at 1.4 and 5 GHz (21 and 6cm), is not resolved by the WSRT, thus we observed the total flux density of the system. The time-averaged 5 and 1.4-GHz flux densities are 35.4 +/-0.4 mJy and 26.4 +/- 0.3 mJy, respectively These give a time-averaged spectral index of alpha (5-1.4 GHz) approximate to 0.23 +/- 0.04, where S-nu proportional to nu (alpha). The departure from the value expected for thermal radiation from a spherically symmetric stellar wind, alpha = 0.6, call be attributed to non-thermal emission from a bow-shaped source to the north of the thermal source associated with the WN8 star. With a possible detection at 350 WHz of 16 +/- mJy, in our separate study of the Cygnus region, the spectral energy distribution, after the contribution of the southern thermal source is subtracted, can be fitted by a synchrotron emission model which includes free-free absorption. The nonthermal emission originates in the region where the winds of the binary components collide. This region, therefore, contains a mixture of relativistic particles accelerated by shocks and thermal particles, responsible for the free-free absorption. We show, in a simplified model of the system, that additional free-free absorption may occur when the line of sight to the collision region passes through the radiophotosphere of the WR wind. The 1.4-GHz flux density of WR 147 varied between similar to 20 mJy and similar to 30 mJy. We attribute the irregular, stochastic variations with a typical timescale of about 60 days to inhomogeneities in the wind, with different mechanisms involved in the flux-density increase than in the flux-density decrease. A flux-density increase results when the inhomogeneities in the wind/clumps enter the wind collision region, fuelling the synchrotron emission. The typical timescale of the flux-density decrease is shorter than the timescale of synchrotron loss (similar to 10(3) yr) or the Inverse-Compton lifetime (approximate to4.5 yr), but of the order of the Row time in the colliding-wind region (similar to 80 d). Therefore, we suggest that the flux-density decrease is due to plasma outflow from the system. Furthermore. variable free-free absorption due to large clumps passing the line of sight may also cause variations in the flux density. We observe a possible long-term flux-density variation oil top of the stochastic variation. This variation is fitted with a sinusoid with a similar to7.9-yr period, with a reduced chi (2) of 1.9. However. as the period of the sinusoid is too close to the monitoring time span, further monitoring is needed to confirm this lon-term variation.

Archiving multi‐epoch data and the discovery of variables in the near‐infrared

We present a description of the design and usage of a new synoptic pipeline and data base model for time series photometry in the VISTA Data Flow System (VDFS). All UK Infra-Red Telescope Wide Field Camera (UKIRT) data and most of the VISTA main survey data will be processed and archived by the VDFS. Much of these data are multi-epoch, useful for finding moving and variable objects. Our new data base design allows the users to easily find rare objects of these types amongst the huge volume of data being produced by modern survey telescopes. Its effectiveness is demonstrated through examples using Data Release 5 of the UKIRT Deep Infrared Sky Survey (UKIDSS-Deep Extragalactic Survey (DXS) and the Wide Field Camera standard star data. The synoptic pipeline provides additional quality control and calibration to these data in the process of generating accurate light curves. We find that 0.6 ± 0.1 per cent of stars and 2.3 ± 0.6 per cent of galaxies in the UKIDSS-DXS with K 0.015 mag.

Near-infrared spectroscopic monitoring of WR 140 during the 2001 periastron passage

W epresent new spectra of WR 140 (HD 193793) in the JHK bands, with some covering the 1.083- mH e Iemission line at higher resolution, observed between 2000 October and 2003 May to cover its 2001 periastron passage and maximum colliding-wind activity. The WC7 O4—5 spectroscopic binary WR 140 is the prototype of colliding-wind, episodic dust-making Wolf—Rayet systems, which also show strong variations in radio and X-ray emission. The JHK spectra showed changes in continuum and in the equivalent widths of the WC emission lines, consistent with the formation of dust, starting between 2001 January 3 and March 26 (orbital phases 0.989 and 0.017) and its subsequent fading and cooling. The 1.083- mH e Iline has a P Cygni profile, which showed variations in both absorption and emission components as WR 140 went through periastron passage. The variation of the absorption component of the profile yielded tight constraints on the geometry of the wind-collision region, giving 50 8 for the opening semi-angle of the interaction region ‘cone’, indicating a wind-momentum ratio ( œ M )O ( œ M )WR 0 10, about three times larger than previously believed. As the system approached periastron, the normally flat-topped emission component of the 1.083- m line profile showed the appearance of a significant subpeak. The movement of the subpeak across the profile was seen to be consistent with its formation in wind material flowing along the contact discontinuity between the WC7 and O4—5 stellar winds and the changing orientation of the colliding-wind region as the stars moved in their orbits. The flux carried in the subpeak was significant, exceeding the X-ray fluxes measured at previous periastron passages. This additional source of radiative cooling of the shock-heated gas probably causes it to depart from being adiabatic around periastron passage, thereby accounting for the departure of the X-ray flux from its previously expected 1 d dependence.