14

SUN/223.7

Starlink Project
Starlink User Note 223.7

D.S. Berry & T.M. Gledhill

14th December 2020

POLPACK
An Imaging Polarimetry Reduction Package

Version 3.6-3

Users’ Manual

pdfpict

Abstract

POLPACK is a package of applications for reducing imaging polarimetry or spectropolarimetry data. They cover registration, sky subtraction, calculation of Stokes parameters, and display of vector maps.

The polarization map on the front cover shows 850 $μ$ m dust grain emission in the cloud core W3. The map shows large scale magnetic fields in this region of high-mass star-formation. The data were obtained with the SCUBA polarimeter on the James Clerk Maxwell Telescope (operated by the Joint Astronomy Centre in Hawaii), and reduced using SURF and POLPACK.

Contents

1 Introduction
1.1 Single-beam Facilities
1.2 Dual-beam Facilities
2 Dual-beam Polarimetry
2.1 The Polarimeter
2.2 The Observational Procedure
2.3 The Data Reduction
  2.3.1 Corrections Related to the Detector
  2.3.2 Extraction of the O and E Ray Images
  2.3.3 Image Alignment
  2.3.4 Sky Subtraction
  2.3.5 Estimation of the Stokes Parameters
  2.3.6 Binning of the Stokes Parameters
  2.3.7 Calculation of the Degree and Orientation of the Polarization
  2.3.8 Display of the Final Polarization Data
3 Single-beam Polarimetry
3.1 The Polarimeter
3.2 The Observational Procedure
3.3 The Data Reduction
4 Spectropolarimetry Data Reduction
5 Data Reduction Using POLPACK
5.1 Format Conversion
5.2 Corrections for Instrumental Effects
5.3 Starting up POLPACK
5.4 Importing Header Information
5.5 Reference Directions
5.6 Creation of Stokes Parameters
5.7 Displaying the Results
  5.7.1 Displaying Spectropolarimetry Data
5.8 Getting Help
5.9 Using RA/DEC Information
  5.9.1 Adding an RA/DEC Calibration to your Data
  5.9.2 Annotating Axes with RA/DEC Values
  5.9.3 Aligning Vector Maps with Other Images
  5.9.4 Re-instating Lost WCS Information in a Catalogue
6 Running from the C-shell
7 Group Expressions
7.1 Indirection
7.2 Modification
7.3 Groups of Data Files
7.4 Examples
8 Trouble-shooting
9 Acknowledging this Software
A Description of the POLPACK applications
A.1 Alphabetic list of POLPACK routines.
A.2 Complete routine descriptions

POLBIN – Bins a catalogue containing Stokes parameters

POLCAL – Converts a set of analysed intensity images into a cube holding Stokes vectors

POLCONCAT – Concatenate two or more vector catalogues

POLEDIT – Change the values in a vector catalogue

POLEXP – Copies information from the POLPACK extension to named FITS keywords

POLEXT – Sets explicit values in the POLPACK extension

POLHELP – Display information about POLPACK

POLIMAGE – Converts a catalogue into an NDF

POLIMP – Copies FITS keyword values into the POLPACK extension

POLKA – Creates Stokes vectors from a set of 2-dimensional intensity frames

POLPLOT – Plots a 2-dimensional vector map

POLROTREF – Rotate the reference direction in a pair of Q and U images

POLSELECT – Select vectors from a catalogue

POLSIM – Produces intensity data corresponding to given Stokes vectors

POLSTACK – Stack a set of intensity images

POLVEC – Calculates polarization vectors from supplied Stokes parameters

POLVERSION – Checks the package version number

POLWCSCOPY – Copies WCS from one catalogue to another

B Calculating the Polarization for Dual-beam Data
C Dual-beam Flat-field Corrections, and the E and F-Factors
D Using GAIA to Create an RA/DEC Calibration
E Calculation of Stokes Vectors in Single-beam Mode
E.1 The Noise Level in Individual Input Images
E.2 Using POLSIM to Investigate Noise Characteristics
F The POLPACK NDF Extension
G History
G.1 V3.6-2
G.2 V3.6-1
G.3 V3.6-0
G.4 V3.5-0
G.5 V3.4-0
G.6 V3.3-0
G.7 V3.2-0
G.8 V3.1-5
G.9 V3.1-3
G.10 V3.1
G.11 V3.0
G.12 V2.1-7
G.13 V2.1-5
G.14 V2.0-14
G.15 V2.0
G.16 V1.1
H Backpage alphabetic listing