1 Introduction

 1.1 Single-beam Facilities
 1.2 Dual-beam Facilities

POLPACK is a package of applications for mapping the linear or circular polarization of extended astronomical objects, either in a single waveband, or in multiple wavebands (spectropolarimetry). Data from both single and dual beam polarimeters can be processed1.

POLPACK processes data in NDF format. This is the standard data format used by most Starlink software, and is described fully in SUN/33. However, other astronomical data formats may also be processed using transparent on-the-fly data conversion facilities provided by the NDF subroutine library, and the CONVERT package. The use of these facilities is described in section 5.1, and more fully in SUN/55.

The facilities provided by POLPACK include:

POLPACK does not provide facilities for performing instrumental corrections such as flat-fielding, de-biassing, etc. Such corrections should be applied to the data before using POLPACK, so that POLPACK can assume that pixel values are proportional to the combined intensity of sky and object. Further comments on these corrections can be found in section 5.2.

Slightly different facilities are available when using single-beam or dual-beam data, as described in the following sections2.

1.1 Single-beam Facilities

1.2 Dual-beam Facilities

1At the moment, circular polarization can only be measured when using dual-beam data.

2It is hoped to rationalize the differences between these two modes in future releases.