Virtual Observatory use case
The Virtual Observatory produces a unified virtual data and service resource with the ability to perform complex data discovery and manipulation of tasks across the whole range of astronomical resources provided by distributed Astronomical Data Centres. The IVOA developed a set of standards, services and applications that are commonly and widely used by Astronomers to access archives and catalogues and to perform operations on observed data.
Discovery of brown dwarfs mining the 2MASS and SDSS databases
To develop science gateways that enable Astronomers to access at the same time computing and IVO data resources, it is necessary to implement a set of data-oriented workflows to access Virtual Observatory resources. We implemented workflows based on AstroTAVERNA plugins as data-oriented workflow modules that are used to access and manipulate data.
In particular, we implemented both AstroTAVERNA Plugin workflows as simple ATOMIC operations that can be re-used as basic components (sub-workflows) of other more complex meta-workflows that represent Astronomical use cases. Moreover those ATOMIC workflows are used also in the implementation of SSP science gateways as simple operations.
IVO workflow name and type
Making the DCI and IVO resource interoperable is a key activity for astronomers since the advent of the grid e-infrastructures in Europe. Those workflows help in solving this problem as they give SSP the ability not only to interact with DCI resources but also with IVO ones, hiding the complexity of the computing and data infrastructure and allowing to focus only on the scientific problem.
Moreover it gives to Astronomical Data Centres the unique opportunity to develop SSP based science gateways to access data using IVO standards/services and to analyse and reduce these data on DCIs.
During Y2 we built a "library" of ATOMIC workflows based on AstroTAVERNA to use as basic modules of more complex workflows.
We implemented a few AstroTAVERNA based workflows as shown in Table 5; we discuss here the steps of one application (HST cone search) and one ATOMIC workflow (VOTable Concatenation).
Retrieving information from HST Cone Search workflow
The Hubble Space Telescope (HST) archive offers access to the HST observations using a VO service. Data can be retrieved in the form of FITS files or VOTables. The cone search workflow is presented in Figure 3. This workflow performs a cone-search around a point in the Sky. The input of the workflow is an ASCII file with a list of source names. First this file is converted into a VOTable, then an extra-column is added for the coordinates that are necessary to query the SIAP image service. The HST SIAP service is queried. The final result consists in two different VOTables issued as the response of both VO Services; Images VOTable have been previously filtered.
One of the common tasks to do when working on astronomical data is to combine data retrieved from archives or catalogues. The workflow presented in Figure 4 is an example of ATOMIC workflow that can be implemented as a light-weight module into more complex workflows.
It accepts VOTables as input data, then it combines them into a vertically replicated singe table.
We queried the HST cone search service from Space Telescope for records within .05 degrees of each Messier object contained in a local input file. The sky positions in the input catalogue are guessed from the available table metadata.
HST WSPC2 calibrated image
The result is a catalogue of objects with their coordinates (RA, DEC), the instrument used, the date and characteristic of the observation. The link to the associated images and image type (DARK, BIAS, FLAT, IMAGE) is also provided.
We calibrated the images and we made the photometric analysis. In the figure we present the result of a calibrated image at RA: 03 32 21.90 and Dec: -27 49 29.82 observed the 4th of September 2005 at 9:40PM; the calibrated image has been queried from the HST archive. The exposure time is 1000 seconds, the instrument used is the Wide-Field Planetary Camera 2 and the filter adopted is the F300W.
- Castelli, G., Taffoni, G., Sciacca, E., et al. "VO-compliant workflows and science gateways", 2014, A&C submitted.