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Last modified: 28 August 2013

How can I cross-match my list of sources with the CSC?


The [New]CSCview Crossmatch feature allows you to query the catalog to locate CSC counterparts to sources of interest by uploading, transmitting, or directly entering a table of source positions (and optionally, position errors) into the GUI. To learn about the crossmatch, refer to the CSCview Help page, the CSC science thread X-ray Spectra of High-z, Radio-quiet Quasars, and the How & Why topic CSCview: Crossmatch Probability Calculation.

An alternate method available for performing a cross-match of your source list against the CSC is using the TOPCAT multiple cone search capability, detailed below. TOPCAT is an interactive graphical viewer and editor for tabular data which facilitates the need for analysis and manipulation of source catalogs.

Here are the detailed instructions for loading your source list into TOPCAT to find CSC counterparts. The output list contains only those sources in your input list which were located in the CSC, along with a select number of source properties from the CSC.

1) Open TOPCAT - which can be downloaded here - and load the table of source positions that you want to cross-match with the CSC by selecting File -> Load Table.


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Several different file formats are supported. In order to load a tab-delimited file, the "ASCII" format must be selected, since selecting "auto" format may yield an error. Here is an example of such a file, with the RA and Dec columns labeled and commented with a leading '#' character, and the columns of data separated by a single tab:

unix% more radec.txt

#RA     Dec

120.58473       -39.86654
120.63274       -39.86152
120.60087       -39.97886
120.68548       -39.92026
120.48381       -40.02003
120.74828       -40.08573
120.46655       -40.09485
120.76748       -39.88891
120.84490       -39.86628
120.55915       -39.91212
120.54483       -39.89668
120.65904       -39.88517
120.70629       -39.80102
120.65896       -39.88036
120.70120       -39.89945
120.60530       -39.78916
120.53209       -39.99421
120.59876       -40.00524
120.44642       -39.78023
120.40584       -39.90480
120.67390       -39.80267
120.58595       -39.87119
120.63886       -39.86500
120.65851       -39.86454

Note that the RA and Dec values in the uploaded table should be in decimal format (decimal hours for RA and decimal degrees for Dec), and not sexagesimal.

In order to load a table of CSCview search results (cscresults.txt) into TOPCAT, the file format "TST" must be selected. The output coordinate format of RA and Dec values in a CSCview results table may be specified as 'decimal' in the Edit->Preferences menu option in CSCview, before saving the file with File->Save. See the CSCview threads to learn more about creating and saving a text file of CSCview search results.

2) Next, click on the table name in the main TOPCAT window to display the table in a separate "Table Browser" window.

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3) With the table selected in the main TOPCAT window, open VO -> Multicone,

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and enter the CSC VO Cone Search URL http://cda.cfa.harvard.edu/cscvo/coneSearch? into the appropriate field under Multiple Cone Search Parameters. (Another option is to enter "CSC" into the Keyword field under Available Cone Search Services and click Submit Query to automatically resolve the CSC, ensuring that the selected registry is http://registry.euro-vo.org/services/RegistrySearch).

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The name of the loaded table should appear in the Input Table field, and the RA and Dec column names should be automatically resolved in the RA column and Dec column fields; if not, enter the appropriate column names and ensure the appropriate units are set. The Search Radius column field can be set to the name of a column in the input table if the search radius should vary from object to object, or alternatively, a fixed radius for the match can be entered.

Clicking Go will perform the cross-match, and the results will be reported in a new table named "cones(1)".

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A note on performance:

The TOPCAT multiple cone search requires approximately .02 seconds to match each row in an input table using a search radius of 3 arcseconds, on Mac 0S X 10.4 PPC and 10.5 Intel (which, for example, would result in a total run time of approximately 3.3 minutes for a list of 10,000 source positions). On Linux CentOS, the run time is approximately .013 seconds per row of an input table (approximately 2.2 minutes for a list of 10,000 source positions).

If you will be matching a large number of sources, it is recommended that you set the "Error Handling" field in the Multiple Cone Search window to one of the options other than the default 'abort', to prevent the search from aborting if an error is encountered during the search.



Last modified: 28 August 2013
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