Mark Cropper

Gaia Data Flow System (GDFS) project: the UK's contribution to Gaia data processing

Gaia is an approved ESA cornerstone project, currently scheduled for launch in late 2011. Gaia will provide photometric, positional, spectroscopic and radial velocity measurements with the accuracies needed to produce a stereoscopic and kinematic census of about one billion stars in our Galaxy and throughout the Local Group, addressing its core science goals to quantify the formation and assembly history of a large spiral galaxy, the Milky Way. Gaia will achieve this by obtaining a six-dimensional (spatial & kinematic) phase-space map of the Galaxy, complemented by an optimised high-spatial resolution multi-colour photometric survey, and the largest stellar spectroscopic and radial velocity surveys ever made. The Gaia data set will be constructed from 2 × 1012 observations (image CCD transits), whose analysis is a very complex task, involving both real-time (this proposal) and end-of-mission data products. This paper describes the UK Gaia Data Flow System activities as part of the emerging European wide Gaia Data Processing system. We describe the data processing challenges that need to be overcome to meet the heavy demands placed by Gaia. We note the construction processes required to handle the photometric reduction of the data from Gaias 100+ focal plane CCDs, the pipeline needed to support the science alerts and epoch photometry handling, and the spectroscopic processing system. We note the system software and hardware architecture, and how the data products will be generated to ensure compliance with emerging VO standards.

Ultra-Short Period Double-Degenerate Binaries

We review the current observational status of the ROSAT sources RX J1914.4+2456 and RX J0806.3+1527, and the evidence that these are ultra-short period (<10min) binary systems. We argue that an Intermediate Polar interpretation can be ruled out, that they are indeed compact binaries with a degenerate secondary, and that the period seen in the X-ray and optical is the orbital period. A white dwarf primary is preferred, but a neutron star cannot be excluded. We examine the capability of the three current double-degenerate models (Polar, Direct Accretor and Electric Star) to account for the observational characteristics of these systems. All models have difficulties with some aspects of the observations, but none can be excluded with confidence at present. The Electric Star model provides the best description, but the lifetime of this phase requires further investigation. These ultra-short period binaries will be strong gravitational wave emitters in the LISA bandpass, and because of their known source properties will be important early targets for gravitational wave studies.

Simultaneous optical and EUVE Observations of the IP PQ Gem

The CV PQ Gem is thought by many to be the first truly ‘Intermediate’ Polar in that it displays characteristics typical of the synchronous and high magnetic field strength ( B ~10–230MG) AM Her systems as well as those of the asynchronous (and much weaker magnetic field strength) Intermediate Polar systems. Here we present the results of quasi-simultaneous optical photopolarimetric and EUVE observations.

White dwarf masses in magnetic CVs: multi-temperature fits to GINGA data

We have used the hard X-ray spectrum obtained from Ginga to determine the mass of the white dwarf primary star in 13 magnetic CV systems. Our model for the spectral fit includes the temperature and density structure in the post-shock accretion flow, taking into account the additional cooling of the cyclotron radiation. We obtain good fits to the data, and we compare our derived masses to those determined by other means.