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In some cases, the table describing the data will contain a so-called DataLink document that links the primary data product (often an image or cube) to related data products (e.g. raw visibilities, calibration solutions). The types of data relations that are allowed within the VO are gathered in a vocabulary. This makes it easier to make the results machine-readable.
Another relevant VO standard to mention here is the Simple Application Messaging Protocol (SAMP). This protocol makes it possible for applications to share information. This allows users to for example query the VO with one application, visuaklise the results with another and do analysis with a third one.
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The data published in the VO can also be accessed using a web browser at https://vo.astron.nl. The web interface can be used to perform simple queries. The power of the VO lies in the fact that several applications exist that can interact with the standards we offer. In the architecture, there is a distinction between services and tables. A service is an entity that takes user input and provides a table as output. The tables themselves are the entities that actually hold the data. Tables can also be queried directly, for instance using ADQL. The colomns of the table are:
Service name name | The (human-readable) name of the service |
| Type | The type of this service. Serrvices of type system are not coupled to specific data collections. The services that provide access to data are either of type image or cube. The image cutout services also offer images, but those are cutouts as define above. Finally there are catalogues which are either catalogues of astrophysical objects, or catalogues which tabulate the properties of the raw data files, that can be used to request them for download (in the Apertif DR1 case). |
| Table name | Name of the table in the TAP service, or N/A for services that are not directly querying a table. |
| Service description | Human-readable description of the service |
| Link to col. descs | Link to the service info page in DACHS. For services that relate to a table (i.e. anything but the system services), this will contain three tables listing columns. The first table shows the input fields, which are the fields that can be used to query the service (typically those are RA, DEC and search radius). The next table shows the default output of a query, which is the subset of the table that has a verbosity of 20 or less. The third table shows all the columns present in the data table, including the ones with verbosity levels higher than 20. In the examples we will show how to access those columns. The table columns on the service info page show the column name (i.e. the term to query on using ADQL), the table header (e,g. when querying on DACHS this ends up as the table header for a column), a human-readable description, the unit of the data in this field, and the Unified Content Descriptor (UCD) which is a machine-readable definition of the data in the column. The goal of a UCD is to make sure that clients know how to handle the data in the column. For the average user those are probably not too relevant. |
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| Service name | Type | Table name | Service description | Service info |
|---|---|---|---|---|
| ADQL Query | system | N/A | This provides a form that can be used to perform ADQL queries and get results in different formats. | info (no columns) |
| LBCS Calibrator Search | catalogue | lbcs.main | Catalog of calibrators from the | info |
| LoLSS - Image Cutout Service | image cutout | lolss.mosaic | info | |
| LoLSS source catalog | catalogue | lolss.source_catalog | Source catalogue of the | info |
| LoTSS-DR1 Cross-Matched Source Catalogue | catalogue | hetdex.main_merged | info | |
| LoTSS-DR1 Image Archive | image | hetdex.hetdex_images | Images of the . | info |
| LoTSS-DR1 Image Cutout Service | image cutout | hetdex.hetdex_images | Cutouts from the images of the . | info |
| LoTSS-DR1 Raw Radio Catalogue Cone Search | catalogue | hetdex.main | info | |
| LoTSS-PDR Image Archive | image | lofartier1.img_main | Images of the . | info |
| LoTSS-PDR Image Cutout Service | image cutout | lofartier1.img_main | Cutouts from the images of the . | info |
| LoTSS-PDR Source Catalogue | catalogue | lofartier1.main | info | |
| M) Apertif DR1 - Continuum images | image | apertif_dr1.continuum_images | Continuum images of the Apertif First Data Release (Apertif DR1). | info |
| M) Apertif DR1 - HI spectral cubes | cube | apertif_dr1.spectral_cubes | HI spectral cubes of the Apertif First Data Release (Apertif DR1). | info |
| M) Apertif DR1 - Polarization images and cubes | image/cube | apertif_dr1.pol_cubes | Stokes V image and Stokes Q and U cubes of the Apertif First Data Release (Apertif DR1). | info |
| MSSS Verification Field Images | image | mvf.msssvf_img_main | info | |
| MSSS Verification Field Sources | catalogue | mvf.main | info | |
| S) Apertif DR1 - Field calibrated visibilities | catalogue | apertif_dr1.calibrated_visibilities | Catalogue of the properties from the calibrated visibilities of the fields from the Apertif First Data Release (Apertif DR1). | info |
| S) Apertif DR1 - Field raw visibilities | catalogue | apertif_dr1.raw_visibilities | Catalogue of the properties from the raw visibilities of the fields from the from the Apertif First Data Release (Apertif DR1). | info |
| S) Apertif DR1 - Flux calibrator raw visibilities | catalogue | apertif_dr1.flux_cal_visibilities | Catalogue of the properties from the calibrated visibilities of the flux calibrators from the Apertif First Data Release (Apertif DR1). | info |
| S) Apertif DR1 - Pol. calibrator raw visibilities | catalogue | apertif_dr1.pol_cal_visibilities | Catalogue of the properties from the calibrated visibilities of the polarisation calibrators from the Apertif First Data Release (Apertif DR1). | info |
| SAURON HI Survey Images | image | sauron.mom0 | info | |
| SAURON HI Survey Velocity Fields | image | sauron.main | info | |
| TGSSADR Image Archive | image | tgssadr.img_main | Images of the | info |
| TGSSADR Image Cutout Service | image cutout | tgssadr.img_main | Cutouts from the images of the | info |
| TGSSADR Source Catalogue | catalogue | tgssadr.main | Catalogue of the radio sources in the . | info |
| The VO @ ASTRON TAP service | system | N/A | (info only): description on how to access the tables using the the TAP protocol. | info (no columns) |
| Apertif DR1 beam cubes (table only, no service) | apertif_dr1.beam_cubes | Beam cubes from the Apertif First Data Release (Apertif DR1), no connected service but accessible via TAP and linked from the other Apertif DR1 tables through DataLink. | N/A |
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Selecting a data collection allows the user to perform a cone search through a webform (Fig. 1). The result is either a source or Gaussian list, or a table of data products of that given class overlapping a given pointing. The size of the continuum images as well as the cubes extend beyond the 10% primary beam level for cleaning the secondary lobes of bright offset sources. To ensure that the search is done in the area of maximum sensitivity the search is performed on a maxim radius of 0.75 degrees from the center (this represents the average value of where the sensitivity drops). This value can be modified using the Max distance from center. A different output with respect to the default can be customized using More output fields selection button.
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 Fig. 1 Query search form for continuum images.
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The result is a table in the requested output format in which every row corresponds to a data product (Fig. 41).
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