SC/22

Starlink Project
Starlink Cookbook 22

H. A. L. Parsons, D. S. Berry, M. G. Rawlings, and S. F. Graves

2021 July 15

Copyright © 2021 East Asian Observatory

The POL-2 Data Reduction Cookbook

1.1


Abstract

This cookbook provides an introduction to POL-2 data reduction, using the Starlink facilities Smurf(the Sub-Millimetre User Reduction Facility) and in particular its command pol2map. This cookbook illustrates the various steps required to reduce the data, including an overview of the method. It also describes how to calibrate and display the data as images or vector maps.

Contents

Acronyms
1 Introduction
 1.1 This cookbook
 1.2 Before you start: computing resources
 1.3 Before you start: software
  1.3.1 Data formats
  1.3.2 Initialising Starlink
  1.3.3 KAPPA and SMURF for data processing
  1.3.4 GAIA for viewing your images and vector maps
  1.3.5 How to get help
2 POL-2 Overview
 2.1 The instrument
 2.2 Instrumental Polarisation
 2.3 Observing mode
 2.4 The raw data
3 POL-2 Data Reduction – The Theory
 3.1 The data flow
 3.2 MAKEMAP
 3.3 SKYLOOP
 3.4 CALCQU
 3.5 PCA
 3.6 Masking
 3.7 Tailoring a reduction
4 POL-2 Data Reduction – Running pol2map
 4.1 How to use pol2map
 4.2 pol2map – producing the initial I map
 4.3 pol2map – producing the I, V, U maps and catalogue
 4.4 Output vectors from pol2map
 4.5 POL-2 FCFs
 4.6 Changing pixel size in pol2map
5 POL-2 Image Display
 5.1 GAIA
 5.2 KAPPA and POLPACK
  5.2.1 Example 1 – a vector map with no background
  5.2.2 Example 2 – a vector map over a contour map
  5.2.3 Example 3 – a vector map over an image
 5.3 TOPCAT
6 POL-2 – Advanced Data Reduction
 6.1 Adding new observations
 6.2 Experimenting with pixel sizes
 6.3 Investigating systematic error in IP
 6.4 Adding WCS information back into a vector catalogue
 6.5 Re-modelling the error estimates in a POL-2 vector catalogue
 6.6 Changing the de-biasing in a POL-2 vector catalogue
 6.7 Smoothing 450-µm POL-2 maps to 850-µm-map resolution
 6.8 Controlling the masks used by pol2map
 6.9 Checking for convergence in pol2map log files
 6.10 Combining multiple POL-2 fields
 References
A PCA on SCUBA-2 data

Acronyms

CADC Canadian Astronomy Data Centre
FCF Flux Conversion Factor
FITS Flexible Image Transport System
GAIA Graphical Astronomy and Image Analysis tool
HWP Half-Wave Plate
ITC Integration Time Calculator
I Total intensity
IP Instrumental Polarisation
JCMT James Clerk Maxwell Telescope
NDF Extensible N-Dimensional Data Format
P Percentage polarisation
PCA Principal Component Analysis
Ip Polarised intensity
SCUBA-2 Submillimetre Common User Bolometer Array-2
SMURF Sub-Millimetre User Reduction Facility
SNR Signal-to-noise ratio
SUN Starlink User Note
WCS World Coordinate System

Bibliography

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[12]   Draper P. W., Gray N., Berry D. S., Taylor M., 2012, GAIA – Graphical Astronomy and Image Analysis Tool, Starlink User Note 214

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[19]   Scott D., Van Engelen A., 2005, Scan Mode Strategies for SCUBA-2, SCUBA-2 Data Reduction document SC2/ANA/S210/005