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The data published in the VO can also be accessed using a web browser at https://vo.astron.nl. This web interface provides a page on which all the collections present in the registry are listed, including the published LoTSS DR2 data sets:
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| anchor | voservices |
|---|---|
| name | Table |
| caption | List of LoTSS DR2 services in the ASTRON VO. |
| Service name | Service Description |
|---|---|
LoTSS-DR2 Gaussian catalog cone search | |
| LoTSS-DR2 Source catalog cone search | |
| LoTSS-DR2 mosaics |
Selecting a data collection allows the user to perform a cone search through a webform (Fig. 40) for all . 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. 40 Query search form for continuum images. |
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In each row there is a column, Product key, which is a link that allows the user to download the fits file of the image or the cube of interest. The column titles should generally be self-descriptive. However, the long human-readable description of the content of each column is a tooltip that will appear when hovering over the column name.
The selected target and the position of the individual pointings The selected target and the position of the individual beams can be visualized using the Quick plot button at the top of the window of the results of the search query (Fig. 41).
In the column Related products another link connects to a page containing a list of links to additional related data that can be useful to interpret or reanalyze that given product (e.g. primary beam images), for which a preview is provided (Fig. 42).
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  Fig. 41 Result of the an image search query. Click for a bigger image. |
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  Fig. 42 Links of ancillary to data products related to the target of interest. Click for a bigger imageThe top two items represent the primary data product (ie the one that can be directly downloaded from the table view) and a link to the thumbnail of that data product. The other products are the anciliary data. Click for a bigger image. Note that the number of related products is too long to fit readably in a single screen shot. |
Some data products are directly accessible, in which case the link on this table will initiate a direct download. However, the larger (and rawer) data products are stored on tape (in which case the text 'on tape' appears in the description). The link will then bring you to the entry of the corresponding pointing in the SURF Data repository (Fig. 43/1). If data is on tape, the status is either "online", in which case it can be downloaded by pressing the "Download" button, or "offline" in which case it can be requested to be put online by pressing the "Request" button. Please note that you need to be logged in to perform the request. If a request has been correctly performed, the status of the file will change to "staging" unill it becomes "online".
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 Fig. 43/1 Surf Data Repository view of the data from a pointing. Click for a bigger image. |
The source and Gaussian cone search forms each return a table with source positions and properties. As before, the long descriptions are available using tool tips. The columns "Mosaic_URL" links to the anciliary data product page of the mosaic from where the Gaussian or source was extracted (like e.g. Fig 42).
The columns shown in Figure 41 are the most informative The columns shown in Figure 3 are the most informative for the astronomers (e.g. position, observing frequency, observing date, quality assessment, format etc), please note that more columns are available but not displayed here. The complete set of columns can be visualized via topcat as described below or using More output fields selection button in the search query. Querying the released data is also possible using e.g. TOPCAT using TAP. Via the TAP protocol, it is possible to query the registry in a more flexible way using an enriched SQL syntax called ADQL. An example is given in Fig. 43 : click the link indicated with the red ellipse on the left panel Try ADQL and place your ADQL query on the query form.
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 Fig. 43/2 ADQL query form. |
The table names to use in the query form of Fig. 43/2, are summarized in Table 10. The URL for the query is then: https://vo.astron.nl/apertiflotss_dr1dr2/q/{Table name}/form (e.g. httphttps://dop457vo.astron.nl:5555/apertiflotss_dr1dr2/q/apertif_dr1_continuum_imagessrc_cone/form}.
It is possible to query all the available dataproducts at once by using the table ivoa.obscore and by appending to the ADQL statement “where obs_collection=” it is possible to limit the search to the apertif_dr1 only.
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Table name | obscore type | obscore subtype |
|---|---|---|
gauss_cone | table (not an obscore type) | |
src_cone | table (not an obscore type) | |
lotss_dr2_mosaic | image | total intensity map |
apertif_dr1.continuum_images | image | continuum |
apertif_dr1.pol_cubes | cube | polarization cube |
apertif_dr1.spectral_cubes | cube | spectral cube |
apertif_dr1.beam_cubes | cube | dirty beam |
Access via TOPCAT
The Apertif DR1 data collection tables can be accessed using TOPCAT, an interactive graphical viewer and editor for tabular data. The data can be sent from vo.astron.nl to TOPCAT using one of the two protocols: SAMP or TAP. The two subsections below provide a description on how to access the tabular data using either SAMP(link to Send via SAMP subsection) or TAP(link to VO Table Access Protocol (TAP) subsection).
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