The Footprint Database and Web Services of the Herschel Space Observatory

Data from the Herschel Space Observatory is freely available to the public but no uniformly processed catalogue of the observations has been published so far. To date, the Herschel Science Archive does not contain the exact sky coverage (footprint) of individual observations and supports search for measurements based on bounding circles only. Drawing on previous experience in implementing footprint databases, we built the Herschel Footprint Database and Web Services for the Herschel Space Observatory to provide efficient search capabilities for typical astronomical queries. The database was designed with the following main goals in mind: (a) provide a unified data model for meta-data of all instruments and observational modes, (b) quickly find observations covering a selected object and its neighbourThe research was supported by the Hungarian Scientific Research Fund OTKA NN 103244 and OTKA NN 114560 grants and PECS contract 4000109997/13/NL/KML of the ESA and the Hungarian Space office. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA. L. Dobos Department of Physics of Complex Systems, Eötvös Loránd University, Pázmány Péter sétány 1/A, 1117 Budapest, Hungary E-mail: [email protected] E. Varga-Verebélyi, C. Kiss Konkoly Observatory, Research Centre for Astronomy and Earth Sciences Hungarian Academy of Sciences H-1121 Budapest, Konkoly Thege Miklós út 15-17, Hungary E-mail: [email protected], [email protected] E. Verdugo, D. Teyssier, K. Exter, I. Valtchanov European Space Astronomy Centre, European Space Agency Villanueva de la Cañada, 28691 Madrid, Spain E-mail: [email protected], [email protected], [email protected], [email protected] T. Budavári Department of Applied Mathematics and Statistics, The Johns Hopkins University 3400 North Charles Street, Baltimore, Maryland 21218, USA E-mail: [email protected] ar X iv :1 60 6. 03 95 7v 1 [ as tr oph .I M ] 1 3 Ju n 20 16 2 László Dobos et al. hood, (c) quickly find every observation in a larger area of the sky, (d) allow for finding solar system objects crossing observation fields. As a first step, we developed a unified data model of observations of all three Herschel instruments for all pointing and instrument modes. Then, using telescope pointing information and observational meta-data, we compiled a database of footprints. As opposed to methods using pixellation of the sphere, we represent sky coverage in an exact geometric form allowing for precise area calculations. For easier handling of Herschel observation footprints with rather complex shapes, two algorithms were implemented to reduce the outline. Furthermore, a new visualisation tool to plot footprints with various spherical projections was developed. Indexing of the footprints using Hierarchical Triangular Mesh makes it possible to quickly find observations based on sky coverage, time and metadata. The database is accessible via a web site1 and also as a set of REST web service functions, which makes it readily usable from programming environments such as Python or IDL. The web service allows downloading footprint data in various formats including Virtual Observatory standards.