CDS Tools

(developed by S. Derriere)

This tutorial shows the basic use of Simbad, VizieR and Aladin , the 3 main CDS services.

  • SIMBAD contains cross-identifications, data and bibliography for individual objects
  • VizieR gives access to thousands of astronomical catalogues
  • Aladin is an interactive sky atlas


The SIMBAD astronomical database provides basic data, cross-identifications, bibliography and measurements for astronomical objects outside the solar system.

We will use the SIMBAD identifier query, and search for the M67 open cluster.

  • Enter M67 in the search box, make sure only this object is selected, and run the query.
  • Note that the output contains many different informations on this object :
    • The object type (here Open Cluster, Cluster of Stars)
    • Sky coordinates
    • Basic data : magnitudes, proper motions, ...
    • Multiple Identifiers : these are expressed using the Dictionary of Nomenclature of Celestial Objects. Many cross identifications are done in SIMBAD, allowing to resolve several million objects (with their multiple identifiers) into their sky coordinates: this feature is used in Name Resolver services, such as Sesame. M67 and NGC 2682 are two possible identifiers for the same physical object.
    • Bibliographic references : major astronomical journals are systematically searched for all object names, and the correspondence between object names and the bibliographical references are stored in SIMBAD.
    • Various additional measurements, links and visualisation methods are also available.
    • Recently, hierarchical information started being introduced between some SIMBAD objects, for example stars which are cited as members of a star cluster, with the membership probability.

We will study the vincinity of M67. We could do so using the Coordinate query, but we will first use the query around button on the result page :

  • leave the 2 arcmin default radius and click query around
  • you should have 111 objects. Note that the result table is sortable on each column.

So far we only used the default web page interface. The output is highly customisable using the Output options yellow tab :

  • Click on the Output options, it will open in a new browser tab.
  • We will change the Output format to VOTable (the VO standard for exchanging data tables), and check the file output box
  • Press the SAVE button
  • In the SIMBAD query result tab, go back to the M67 single object result page, and query around with a 60 arcmin search radius
  • Save the result file as simbad-M67.xml : we will reuse this file later

Important : Note that you should change back the Output format to HTML and uncheck the file output box if you want to use SIMBAD in your browser after this !


VizieR is a collection of thousands of individual catalogues. They can come from large surveys, mission logs, or electronic versions of tabular data published in refereed journals. Each catalogue has a standardised description file named ReadMe, in which you can find details on its contents. The structure of VizieR is the following :
  • Catalogues : they are the top-level data structures, usually one catalogue corresponds to one paper or survey. One catalogue can contain one or several tables.
  • Tables : if a paper contains multiple tables, they can be accessed individually in the same catalogue.
  • Rows : each table can contain from a few rows to over one billion rows for the largest tables.

VizieR can be used in different progressive steps :

  1. Search for catalogues among all available catalogues
  2. Select relevant catalogues, and/or tables
  3. Set query constraints and output options
  4. Display details for one row of a table of a catalogue
There are multiple shortcuts, and several ways to perform these queries.

We will search for a catalogue created by Frolov (1986), containing data on the Open Cluster M67. This can be done in different ways :

  • Open the main VizieR web form
  • Enter M67 in the Target Name box, and click Find Catalogues
    • There are 227 catalogues containing sources within 2 arcmin of M67 coordinates
  • Go back, remove the target and try Open_Clusters in the Astronomical keywords, and click Find Catalogues
  • Go back, unselect Open_Clusters in the Astronomical keywords, and search Frolov in Words matching author's name, word(s) from title, description, and click Find Catalogues
  • You can combine these criteria to refine the search

We will proceed with the catalogue V/52 Photometry and Proper Motions in M67 (note that II/123A does not contain sky coordinates, and thus is not found by coordinates!). The catalogue V/52 only contains one table named data.

When querying a VizieR table, note that :

  • You can compute additional coordinates, not part of the original data: these will be displayed in orange in the HTML output
  • The default output is limited to 50 rows. Change this value to get all data.
  • Only some of the columns are displayed in the default output (those with Show checkboxes activated). You can choose All cols or customize the output.
  • You can add constraints to filter the output : try querying after setting <11 for the column V(pg).
  • There are multiple output formats in the Output layout menu.

We will perform more advanced queries in the scripting tutorial.

For now, we will save a copy of the table V/52/data, in VOTable format, with all sources and all columns, in a file named vizier-V52.vot


Aladin is a sky atlas, with many features, so we will not cover the 100 pages of manual during this session! It can be used to overlay multiple data on images.

We will use the standalone version, v6.011b.

Instructions given in gray are optional and only for the fastest participants :o)

  1. Start Aladin
  2. Load some local files : File > Open local file or Ctrl+O
    • Open the previously saved simbad-M67.xml and vizier-V52.vot
    • Two planes are created in the Aladin stack
  3. Hover your mouse on the plane name to see details
    • You should have 8097 SIMBAD sources and 1068 VizieR sources
  4. Try to hide/show the planes
  5. Change plane properties for different colors and symbols
  6. Select individual or groups of sources and see the measurements in the bottom panel
  7. Detach/undetach the measurement panel
  8. File > Open, Aladin images
    • You can use Grab coo and click in the view to pick the cenral coordinates
    • Submit and see the list of available images. Select POSSI 486-LOW and Submit
  9. Try to (un)zoom (mouse wheel, or (shift)-click), pan around
  10. Move the SIMBAD and VizieR planes above the image in the stack
  11. Double click on the VizieR plane : this selects all sources. Click on V(pg) to sort on a column
    • Zoom in, click on a data line, and use arrows to browse in the data
  12. Go back to File > Open, Aladin images, load some more images (e.g. POSS, 13.0'x13.0' size)
  13. Load some Sloan images
  14. Click on image planes to switch between them
    • Use sliders or properties to change transparency
  15. Use the multiview to see two images simultaneously. Shift-click to sychronize the views. Zoom and pan around.
    • Create a blink sequence
    • Create a color image
  16. Delete the 2 catalogue planes. We will reload these directly from the corresponding services :
    • File > Open, SIMBAD, Target M67, Radius = 1
    • File > Open, All VizieR : all columns, whole catalogue, Catalogue= V/52
    • Apply a Filter to Frolov data: Draw circles proportional to objects luminosity
  17. Catalogue, Cross match objects : cross match V/52 with SIMBAD data
  18. Search for additional data in the VO
    • File > Open, All VO
    • Use a reasonable radius, 10 or 15'
    • Try to load a few data from other locations

-- SebastienDerriere - 31 May 2010

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Topic revision: r5 - 2010-06-18 - CarolineBot
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