Refining the Pointing Model

Once the telescope has been polar aligned and a rudimentary pointing model has been created (either with the two-star matrix or Tpoint), refining the model is easy. Since the ROTSE-III telescopes have such wide-fields, astrometric calibration can be done from the bright USNO A2.0 catalog stars in the field, and superfine accuracy is not essential. Pointing errors of over 30 arcminutes are usually handled comfortably by the calibration software, but are not desirable for normal operation.

With a simple pointing model installed in the schierd.conf configuration file, the telescope can point to celestial coordinates accurately with rmove and the astronomical scheduler daemon. With a single night of all-sky imaging, a more refined pointing model can be bootstrapped on top of the simple model.

The astrod.conf.pointing sample file contains a list of hundreds of fields evenly gridded across the entire celestial sphere. Whatever fields that are visible from the local site will be used to image the whole sky. An idl program called cobj_to_tp.pro converts the calibrated file output to a form to input into Tpoint, and a refined pointing model can be created. Here are the steps to accomplish this:

1. Copy the pointing fields from /rotse/run/etc/astrod.conf.pointing into the current astrod.conf file.

2. Run on a reasonably clear night. Moon illumination is not important, unless the all-sky data is also being used to calculate a flatfield image.

   For information on how to run the system and start the pipeline, see Chapter 2 and Chapter 8.

3. Copy the object list (cobj) files from the pipeline directory to a temporary directory.

   The pipeline directory should be set to /rotse/data/pipeline/prod/.

4. Create a text file with the list of cobj files.

   $ cd temporary_directory

   $ ls -color=never date_*cobj.fit > cobj.list

5. Start idl and run cobj_to_tp.pro.

   $ idl

   IDL> cobj_to_tp

   syntax - cobj_to_tp,listfile,outname,ptgstr,...

   IDL> cobj_to_tp,'cobj.list','tpointfile.dat',pointing_structure

6. The file tpointfile.dat (or whatever you chose to name it) now has hundreds of stars for Tpoint to create a pointing model.

7. Run Tpoint on tpointfile.dat as described in Section 5.3

8. Update schierd.conf as described in Section 3.8 to use the new Tpoint model file.