Reducing Hydra Cals.

Introduction.

This section describes how to reduce Hydra Cal data into .cal files and then into an .scal file. Cal files just give the system and cal counts on a given patch of sky. scal files give the conversion factor between the cal and Jy. When reducing pulsar observations the software requires an observation of Hydra and a calibration near the pulsar observation. The Hydra observations are made by pressing the "Hydra Cal" button on timer when observing. What then happens is a 6 observation sequence. the first observation is 5 seconds long, it is used to set the attenuator levels on Hydra. Then 5 90 second observations are made North, On, South, On and North of Hydra. These observations are usually about 2 minutes apart.

The first 5 second observation should be deleted. It is not used in subsequent analysis. The remaining observations will have names like:

970201_192323.*

You need to convert these to a .cal file. All you do to do this is type:

rfd2ar filename

This should create a .cal file and move it into $calpool (the directory pointed to by the calpool environment variable). Delete the files once you have reduced them. On a sparc 20 this takes about a minute.

Repeat this procedure for each of the 5 observations.

Now you are ready to create a .scal file. This records how strong the cal was compared to Hydra. To create the .scal file go to $calpool and type:

ar2scal filenames.scal

Watch the output and check that the system is about the right number of Jy.

You are now ready to reduce your Cal and pulsar observation.