SC/6.4

Starlink Project
Starlink Cookbook 6.4

J. Palmer & A.C. Davenhall

31st August 2001

Copyright © 2001 Council for the Central Laboratory of the Research Councils

The CCD Photometric Calibration Cookbook


Abstract

This cookbook presents simple recipes for the photometric calibration of CCD frames. Using these recipes you can calibrate the brightness of objects measured in CCD frames into magnitudes in standard photometric systems, such as the Johnson-Morgan UBV system. The recipes use standard software available at all Starlink sites.

The topics covered include: selecting standard stars, measuring instrumental magnitudes and calibrating instrumental magnitudes into a standard system. The recipes are appropriate for use with data acquired with optical CCDs and filters, operated in standard ways, and describe the usual calibration technique of observing standard stars. The software is robust and reliable, but the techniques are usually not suitable where very high accuracy is required.

In addition to the recipes and scripts, sufficient background material is presented to explain the procedures and techniques used. The treatment is deliberately practical rather than theoretical, in keeping with the aim of providing advice on the actual calibration of observations.

Who Should Read this Cookbook?

This cookbook is aimed firmly at people who are new to astronomical photometry. Typical readers might have a set of photometric observations to reduce (perhaps observed by a colleague) or be planning a programme of photometric observations, perhaps for the first time. No prior knowledge of astronomical photometry is assumed.

The cookbook is not aimed at experts in astronomical photometry. Many finer points are omitted for clarity and brevity. Also, in order to make the most accurate possible calibration of high-precision photometry, it is usually necessary to use bespoke software tailored to the observing programme and photometric system you are using.

Contents

1 Introduction
2 Further Reading
3 Typographic Conventions
4 Introduction
5 Intensity, Flux Density and Luminosity
6 Magnitudes
7 Photometric Systems
 7.1 Colour indices
 7.2 Standard and instrumental systems
 7.3 Catalogues of standard stars
  7.3.1 Computer-readable catalogues
8 Atmospheric Extinction and Air Mass
 8.1 Atmospheric transmission at infrared wavelengths
9 Selecting and Observing Standard Stars
 9.1 Selecting standard stars
 9.2 Observing standard stars
10 Measuring Instrumental Magnitudes
11 Calibrating Instrumental Magnitudes
 11.1 Calibration without a colour correction
 11.2 Calibration with colour corrections
12 Introduction
13 Selecting Standard Stars
14 Measuring Instrumental Magnitudes with PHOTOM
15 Measuring Instrumental Magnitudes with GAIA
16 Calibrating Instrumental Magnitudes
A Interstellar Extinction and Reddening
B Finding the Air Mass and Zenith Distance
 B.1 Information required
 B.2 Examining files
Acknowledgements
References

Revision history

(1)
25 April 1997: Version 1. Original version (JP).
(2)
29 January 1998: Version 2. Added recipes for extracting standard stars from catalogues and calibrating instrumental magnitudes. Also re-arranged much of the existing material (ACD).
(3)
8 June 1999: Version 3. Added material for infrared photometric systems and atmospheric transmission (ACD).
(4)
31 August 2001: Version 4. Revised the recipes to correspond to GAIA version 2.6 and CURSA version 6.3. Added an additional label to allow external hyper-links to Appendix B.2. Also revised the references and URLs (ACD).

Acknowledgements

We are grateful to John Lucey for extensive discussions about photometry and photometric calibration and for providing the example data used in Section 16. Nick Eaton gave useful advice about PHOTOM and Peter Draper about GAIA. Chris Clayton, Malcolm Currie, Simon Dye, Rachel Johnson, Mike Lawden, Sandy Leggett and Ian Waddington all made useful comments on the cookbook.

Any mistakes are, of course, our own.

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