Cross-ID Tutorial

How do I upload my own data to see what the SDSS knows about those objects?

You can provide a list of your own objects, then use the SkyServer  to see what those objects look like in the SDSS. This is especially useful when looking for optical counterparts to objects seen in other wavelengths. The tool to do this is the Imaging Cross-Identification  tool. From the home page, look for CrossID.

Using the Imaging Cross-ID tool

  1. Under Search Type, click the radio button to choose to search based on Images, Spectra, or Infrared Spectra.
  2. Under Search Scope, choose the type of search that you want to do. The options are:
    Nearest Primary Object
    The single primary object nearest to the position that you will enter or upload. Primary object means the best single observation of the object; other observations of the same object may be available.
    Nearest Object
    The object nearest to the position that you will enter or upload, whether or not it is a primary observation.
    All Nearby Primary Objects
    All primary observations of objects within your specified search radius.
    All Nearby Objects
    All objects within your specified search radius.
  3. Enter a search radius (in arcminutes) in the Search Radius textbox. This is the radius around each of your objects that the tool will search as it looks for a matching SDSS object. The maximum radius you can enter is 3 arcminutes.
  4. Enter the number of columns that precede your RA and dec in the textbox labeled Number of preceding non-data columns. For example, if your data consists of (name, ra, dec), enter 1 in this box.
  5. You can enter your data to cross-match (in other words, the list of objects for which you want to see SDSS data) in one of two ways. Either enter it in the textbox labeled Cut and paste your upload list here, or upload a text file using the Choose File button to the right. When there is data in the textbox and a file specified in the upload box, the file takes priority.
  6. Choose the Format you would like results returned in. HTML will return results as a table in your browser. CSV will return results as a comma-separated value file, which can be opened by many graphing programs.
  7. You can change what types of data the query returns by editing the SQL query just above the Format selector. Make sure the photo table/view is aliased as ‘p’ – for example photoTag p. Do not modify the #x and #upload parts of the FROM clause; otherwise your upload will not work.
  8. Click Submit to run your query.
  9. If you have chosen the default options, the query will return the following data: the SDSS Object ID, the position (RA and Dec), the type of object (STAR or GALAXY), and the SDSS’s five magnitudes (u, g, r, i, and z). Click on the object ID to go to the Explore  tool, which will give you more information about the object.

Get SDSS image thumbnails

  1. Once you have the SDSS object ID, RA, and dec of your objects from the CrossID tool, you can get thumbnail images of what the objects look like in the SDSS using the SkyServer Image List  tool.
  2. Copy and paste the object ID, RA, and dec into the textbox in the upper left of the form, just above Cut and Paste ra/dec list. Be sure to leave one space between each piece of data. Click Get Image to return thumbnails of each object. The Image List tool is limited to returning 1,000 objects.
  3. A thumbnail image of each result will come up in a new frame within the same window.
  4. Click on the thumbnail image to go to the Navigate  tool entry for that object. The Navigate tool will give you an image of the object and the area around it, which you can zoom in or out of.
  5. Click on the object’s name (above the thumbnail image) to go to the Explore  tool entry for that object. The Explore tool shows complete data for the object, including a spectrum if one was observed by the SDSS.