ColourCutterComments

Colour Cutter

Summary:

This Astrogrid science service allows the user to select IR and optical objects by region and by colour. It is available via the Workbench or as a Parameterised Workflow from the Portal home page.

How to run the Colour Cutter:

• Portal Home Page: (this gives more prompts)
  • Click on Workflows in the Parameterised Workflows box on the left
  • Select the Colour Cutter
  • Follow the instructions for the input values
    • The examples are used as defaults if a value is left blank
  • Check the button at the bottom if you want to save the workflow to MySpace
  • See information below for more details
• Workbench:
  • Click on Webstart applications on the left of the portal home page, or use to launch the Workbench
  • From the Workbench, select Parameterised Workflows > Run
  • Select the Colour Cutter and use the information below for input choices.
    • Edit the default values in the Task Editor, maintaining the format
  • After clicking OK, if you chose to save the workflow, you can save directly to your disc, MySpace or a URL.

Input parameters

Catalogue	Sky coverage	Bands (enter exact column names)	Wavelengths (approx, micron)	Row limit /source density
2MASS	all sky	j_m h_m k_m	1.24, 1.66, 2.16	10000 per 1 - 20 sq deg
USNO-B	all sky	B1Mag R1Mag NMag	0.4 0.7 10	10000 per 0.2 - 1 sq deg
INT-WFS	region/band details	U B g V r Harris_R i RGO_I z	0.36 0.44 0.48 0.55 0.63 0.64 0.77 0.81 0.91	2000 per 0.05 - 0.1 sq deg

1. Select a celestial region by central coordinate (J2000) plus size of box side; all units are decimal degrees and no curvature correction is made (so near the poles, the actual sky coverage will be compressed in the direction of Right Ascension).
   • This is entered as e.g. 56.75,+23.867,1.0
   • There are row limits for each datacentre which restrict the number of objects which can be returned by a single query. If you have stringent colour restrictions you may cover more sky but, if all objects in a region are returned, the limits are roughly as given below (the source density is highest in mid-northern latitudes for the all-sky catalogues).
2. Your first catalogue is 2MASS, your second must be chosen from USNO-B or INT-WFS
   • See table above for details
3. Select the colour cut conditions for a pair of catalogues such that
   • Band1_mag - Band2_mag > mag_limit
   • This is entered as e.g. j_m,k_m,2.0 (exact band names as in the catalogue).
   • You must select the first pair of bands from 2MASS and the second from one of the two optical catalogues.
   • Selection cannot be made by comparing values in different catalogues but you can do this yourself using TopCat.
4. If the catalogue gives uncertainties, values of Band2 are chosen to have errors in the range [0,0.5] but Band1 may be a non-detection or very uncertain (so the selection may be based on upper limits).
5. The IR and optical colour-selected extracts are crossmatched using a 5 arcsec search radius as the 2MASS uncertainties dominate the position errors in most cases.
6. The main output catalogue (in VOTable format) contains the position of each object, its catalogue ID, and all available principal magnitude measurements (and uncertainties if given) plus the requested colours and uncertainties (if available).

Launching the workflow

Using the Portal

(Click on images to see full-size)	Click on Execute. This launches the workflow. You will be asked if you want to save the workflow document - saving the document into MySpace allows to load the workflow inside the portal, to view it / modify it. In this case, choose a folder and enter the workflow name in the MySpace microbrowser which will appear.
	You should then get a confirmatory message:
	You can click on the ID in the Job Monitor window to see an overview of progress:
	and again for the full transcript, including the names of the output files - or error messages.
	When the status of the job changes to 'COMPLETED', log out of the portal and log in again and go to the MySpace page. You should see a directory representing the position e.g. CCut_RA56.7Dec23.867_1.0 containing files labelled by the selection criteria - e.g. j_m-k_m.gt.1.0.vot (IR); i-z.gt.2.0.vot (optical); j_m-k_m.gt.1.0_and_i-z.gt.2.0.vot* (matched, with colours added). Thus if you re-run a query at the same position but a different colour selection the files will be written to the same directory and the intermediate files (IR.vot, optical.vot), which contain the colours for each data set separately, will be overwritten. The output colour columns are called "ir_colour", "ir_col_err", "opt_colour" and "opt_col_err" (if present).

Using the Workbench

This is under development and will eventually offer easier editing of workflows. Presently, you can use it to launch a parameterised workflow as described above, and also to launch a JobMonitor:

The WorkflowBuilder lets you load the saved workflow (via its File button), which shows more details about its structure:

Further processing

You can download the output to your desktop, but you can also manipulate it further in MySpace, either as input to a separate workflow or in the Aladin or TopCat tools which can be launched from the workbench or the portal home page just like the parameterised workflow. TopCat can be used to sort the data, form more colours etc. and plot the output.

If you saved the workflow, you can load it into the portal and edit it in the Workflow page <align=left> <align=right>

Usage Notes:

Troubleshooting

If the Job monitor reports Completed but you don't see any output, did you log in and out again (to see a new directory) or use the Refresh button on the MySpace page (to see new, or newly overwritten, files).

If the Job monitor reports Error,

• Check the workflow transcript
  • Does the Directory name correspond to a valid position?
  • If the INT-WFS catalogue was chosen, or if a very small box was used, are there data in the search box?
  • Do the file names correspond to the exact band names as used in the catalogue (see prompts in input parameter page or lists above)?
  • You will see a detailed error message further down, if you can't interpret this you can send it to astrogrid.
• Check whether the directory or any files have appeared/been refreshed in MySpace and examine them (e.g. in TopCat.
  • If the separate IR and optical files seem OK but there is no final matched file, perhaps there were no objects in common.
  • If you selected a very large region the row limit may have been exceeded (see table above).

How it works

• The range of RA and Dec to be searched and the colour constraints are written into template queries, one for each catalogue. An additional constraint to select only Band2 values with small errors is added. The queries are in ADQL, an XML translation of SQL specialised for astronomy and solar science.
• For each catalogue selection returned to MySpace, a new column is written for the colour (Band1-Band2) and for the error (simply (sqrt[Band1err^2 + Band2err^2]), where available).
• The 'coloured' catalogue selections are crossmatched, finding all matches within 5 arcsec.
• The matched catalogue is returned to MySpace.

More information on actions not specific to this tool (e.g. using MySpace) can be found

• Using the Portal help buttons or Help page
• Using the help menu within the Workbench
• Using the AstroGrid software page e.g.
  • Click on Use AstroGrid
    • Click on Portal and then use the left-hand menu to get more detailed descriptions of MySpace etc.
    • Click on Workbench to get Workbench documentation

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Development

Features which we hope to add include:

• Making it easier to discover if the region you want contains the bands you want, for catalogues with partial coverage;
• Adding more catalogues
• Allowing Band1 and Band2 to be from different catalogues
• Increasing the number of catalogue rows which can be processed at once.

Priorities will be informed by user feedback, so please let us know what you would like to see. For example, there could be additional inputs to determine the match radius or the error handling could be changed to exclude all catalogue measurements which were lower limits.

See UcPersistentTableJoin for an elegant solution involving querying and crossmatching separate tables in one query, using a MySpace database to handle the intermediate data (VOStore).

Other issues:

• Including on-the-fly source extraction/upper limit measurement from images
• Including user's own data from MySpace or URL
• Providing colour corrections so that the user can enter criteria in a standard photometric system
• Aperture corrections
• Selecting the optimum search radii for multi-catalogue cross-matches
  • Astrometric alignment

These are more challenging but links could be provided to help manual processes (e.g. using Aladin for astrometry).

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-- AnitaRichards - 22 Oct 2005

Colour Cutter Comments

Please add comments here or email the author.

-- RichardMcMahon - 08 Feb 2005

• might want to include option to select/restrict image class in catalogues
  • return only return stellar objects in wave band i
  • return only return objects that are stellar in wave band i and wave band j

• also a colour criterion might use the errors like this to limit the effects of objects with large errors;
  • (X-Y) - 2*sigma(X-Y) > limit in X-Y