XMM-Newton SAS Home Page
XMM-Newton Science Analysis System

omichain (omichain-1.74.9) [xmmsas_20211130_0941-20.0.0]

Running the omichain

Assuming the environment variables SAS_CCFPATH, SAS_CCF and SAS_ODF have been properly defined to process a given ODF data set, you may proceed to run the omichain by simply executing the command omichain, without any parameter.

The location of the ODF files to be processed is obtained from the SAS summary file that is defined in the SAS_ODF environment variable. Should this variable not set or not set properly to be the SAS summary file, omichain will complain and exit with an error message.

All ODF files should be uncompressed. Oherwise some functions in the omichain will not work properly.

It is a good idea to ensure that the SAS environment variable SAS_VERBOSITY is set to at least 5 (setenv SAS_VERBOSITY 5), so that all messages, warnings and errors from the omichain are displayed.

It is also useful to redirect the output to a log file (omichain ...... $>\&$ omichain.log &, c-shell).

  1. Use the command omichain outdirectory=some_path to put all output products in the specified path.

  2. In the following, the term output file refers to a file created by one one of the OM SAS tasks during the run of the omichain. Output products from these tasks are all FITS (Flexible Image Transport System) files except those of type ps (PostScript) and pdf (Portable Document Format), which are the byproducts of plotting tasks.

  3. Using the default parameter settings, the omichain will process all the image files in the ODF directory. However, if only the images of specific exposures or the images taken with specific filters need to be processed, the parameters exposures and filters, respectively, can be used to achieve this as follows:

    1. To specify which filter/filters to process use the parameter filters='filter1 filter2 ...'.
    2. To specify which exposure/exposures to process add the parameter exposures='exposure1 exposure2 ...'.

  4. To exclude source-detection on the mosaiced sky-images add the parameter processmosaicedimages=n.

Some of the parameters for individual tasks can be set using the appropriate omichain parameter - the parameter names are the same as the task parameter names, prefixed with the name of the task - (see section 7).

It should be noted that if running omichain on a large mosaic field (more than around 2 degrees x 2 degrees), the source detection process may encounter memory limits when processing the mosaic images, and fail to complete. Large OM mosaics often have low filling factors and little overlap of exposures, and therefore add little in terms of source detection beyond that achieved from the individual exposure processing. In the case of large mosaics, therefore, it may be advisable to avoid source detection by setting processmosaicedimages=n. Where source detection on mosaics is performed, new detections will be added to the final observation source list.

XMM-Newton SOC -- 2021-11-30