Guy Rixon

Gaia Data Release 1 - The photometric data

Context. This paper presents an overview of the photometric data that are part of the first Gaia data release. Aims. The principles of the processing and the main characteristics of the Gaia photometric data are presented. Methods. The calibration strategy is outlined briefly and the main properties of the resulting photometry are presented. Results. Relations with other broadband photometric systems are provided. The overall precision for the Gaia photometry is shown to be at the milli-magnitude level and has a clear potential to improve further in future releases.

PathGrid: a service-orientated architecture for microscopy image analysis

This paper describes ‘PathGrid’—an analysis and data integration system, developed initially to meet the demands in the analysis of medical microscopy imaging data. An overview of the current system is given, describing the techniques used in developing the data handling infrastructure and the analysis algorithm development. The use of software created in the context of systems designed for the astronomy domain is noted, specifically infrastructure from the astronomy virtual observatory movement for data discovery, access and workflow management, and astronomical image analysis software adapted for the analysis of high-throughput astronomy imaging surveys. This paper notes the applicability of the techniques from the astronomy domain. The testbed infrastructure deployment is described, emphasizing its speed and ease of use and support. The validity of the analysis techniques is confirmed through the pilot study described here—with the application to a large sample of immunohistochemistry microscopy data obtained in part for assessing the oestrogen receptor status of breast cancers. The analysis showed that the specificity and sensitivity values for the automatic scoring using PathGrid were within the errors of those obtained via a ‘gold standard’ manual pathologist scoring.

Visualizing astronomy data using VRML

Visualisation is a powerful tool for understanding the large data sets typical of astronomical surveys and can reveal unsuspected relationships and anomalous regions of parameter space which may be difficult to find programatically. Visualisation is a classic information technology for optimising scientific return. We are developing a number of generic on-line visualisation tools as a component of the Australian Virtual Observatory project. The tools will be deployed within the framework of the International Virtual Observatory Alliance (IVOA), and follow agreed-upon standards to make them accessible by other programs and people. We and our IVOA partners plan to utilise new information technologies (such as grid computing and web services) to advance the scientific return of existing and future instrumentation. Here we present a new tool - VOlume - which visualises point data. Visualisation of astronomical data normally requires the local installation of complex software, the downloading of potentially large datasets, and very often time-consuming and tedious data format conversions. VOlume enables the astronomer to visualise data using just a web browser and plug-in. This is achieved using IVOA standards which allow us to pass data between Web Services, Java Servlet Technology and Common Gateway Interface programs. Data from a catalogue server can be streamed in eXtensible Mark-up Language format to a servlet which produces Virtual Reality Modeling Language output. The user selects elements of the catalogue to map to geometry and then visualises the result in a browser plug-in such as Cortona or FreeWRL. Other than requiring an input VOTable format file, VOlume is very general. While its major use will likely be to display and explore astronomical source catalogues, it can easily render other important parameter fields such as the sky and redshift coverage of proposed surveys or the sampling of the visibility plane by a rotation-synthesis interferometer.

The fast transient sky with Gaia

The ESA Gaia satellite scans the whole sky with a temporal sampling ranging from seconds and hours to months. Each time a source passes within the Gaia field of view, it moves over 10 CCDs in 45 s and a lightcurve with 4.5 s sampling (the crossing time per CCD) is registered. Given that the 4.5 s sampling represents a virtually unexplored parameter space in optical time domain astronomy, this data set potentially provides a unique opportunity to open up the fast transient sky. We present a method to start mining the wealth of information in the per CCD Gaia data. We perform extensive data filtering to eliminate known on-board and data processing artefacts, and present a statistical method to identify sources that show transient brightness variations on ~2 hours timescales. We illustrate that by using the Gaia photometric CCD measurements, we can detect transient brightness variations down to an amplitude of 0.3 mag on timescales ranging from 15 seconds to several hours. We search an area of ~23.5 square degrees on the sky, and find four strong candidate fast transients. Two candidates are tentatively classified as flares on M-dwarf stars, while one is probably a flare on a giant star and one potentially a flare on a solar type star. These classifications are based on archival data and the timescales involved. We argue that the method presented here can be added to the existing Gaia Science Alerts infrastructure for the near real-time public dissemination of fast transient events.

Interoperability of archives in the VO

For the Virtual Observatory to connect archives around the globe, some standardization is needed. It is not necessary to rework the internal structure of each archive to a common standard, but standards for interfaces to archives and for exchange of data are important. We report on standardization work currently going on in the AVO and AstroGRID projects in the following areas: - Exchange formats for tabular data; - Semantic definitions for quantities in tabular data; - Identification of user and authorization to use resources; - Query interfaces to archives; - Catalogues of data resources. Discussion on standards is ongoing among all Virtual Observatory projects.

Identified usage of the Virtual Observatory: beyond the WWW

Current astronomical facilities on the WWW support anonymous access to public-domain resources with very limited workflows. To meet even current aspirations, the Virtual Observatory needs to operate extensive workflows that also include access to restricted resources. AstroGrid (see http://www.astrogrid.org/), a UK eScience project with collaborating groups drawn from the major UK data archive centres, is currently creating the UKs virtual observatory (Lawrence, 2002, these proceedings). We present use cases from AstroGrids survey of requirements that show a need for a pervasive infrastructure for identifying users and controlling access to facilities and data. We describe in outline AstroGrids architecture for this infrastructure.

Gaia transients in galactic nuclei

The high spatial resolution and precise astrometry and photometry of the Gaia mission should make it particularly apt at discovering and resolving transients occurring in, or near, the centres of galaxies. Indeed, some nuclear transients are reported by the Gaia Science Alerts (GSA) team, but not a single confirmed Tidal Disruption Event has been published. In order to explore the sensitivity of GSA, we performed an independent and systematic search for nuclear transients using Gaia observations. Our transient search is driven from an input galaxy catalogue (derived from the Sloan Digital Sky Survey Release 12). We present a candidate detection metric which is independent from the existing GSA methodology, to see if Gaia Alerts are biased against the discovery of nuclear transients, and in particular which steps may have an impact. Our technique does require significant manual vetting of candidates, making implementation in the GSA system impractical for daily operations, although it could be run weekly, which for month-to-year long transients would make a scientifically valuable addition. Our search yielded ~480 nuclear transients, 5 of which were alerted and published by GSA. The list of (in some cases ongoing) transients includes candidates for events related to enhanced accretion onto a super-massive black hole and TDEs. An implementation of the detection methodology and criteria used in this paper as an extension of GSA could open up the possibility for Gaia to fulfil the role as a main tool to find transient nuclear activity as predicted in the literature.

AVO interoperability demonstration

AVO Work Area 2 consists of deployment and demonstration of an interoperability prototype. Access to archives of all the partners (ESO, ESA, AstroGrid, Terapix, Jodrell Bank) is implemented via the CDS data federation and integration tools: VizieR and Aladin. The prototype is available for science usage and more functionalities, based in particular on the usage of Uniform Content Descriptors (UCDs) for data mining, will be developed. Case by case discussion with data providers will help to establish a set of practical recommendations for interoperability. Science requirements and new technologies studied by the other AVO work Areas will also be tested. Discussions on standards are ongoing among all VO projects.

Improving the effectiveness of 2-m-class telescopes through control systems redesign

The computing equipment of the 2.5-m Isaac Newton Telescope and the 1.0-m Jacobus Kapteyn Telescope is being upgraded to improve improve observing efficiency and ease of use, and to reduce maintenance and operation costs. These upgrades have been staged over a period of two years to reduce the impact on operations. Elements of this architecture will be used in the forthcoming upgrades to the 4.2-m William Herschel Telescope. The revised systems have allowed the introduction of a major new instrument for the INT: the Wide Field Camera, shortly to be equipped with a mosaic of four 4096 by 2048 EEV CCDs. On the JKT, the new equipment paves the way for remote operation.