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


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.


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

Revision history

25 April 1997: Version 1. Original version (JP).
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).
8 June 1999: Version 3. Added material for infrared photometric systems and atmospheric transmission (ACD).
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).


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.


[1]   C.W. Allen, 1973, Astrophysical Quantities, third edition (Athlone Press: London).

[2]   D.A. Allen, 1975, Infrared – the New Astronomy (Keith Reid: Shaldon, Devon).

[3]   D.A. Allen and T.A. Cragg, 1983, Mon. Not. R. Astron. Soc, 203, pp777-783.

[4]   M. Bersanelli, P. Bouchet and R. Falomo, 1991, Astron. Astrophys, 252, pp854-860.

[5]   P. Bouchet, J. Manfroid and F.X. Schmider, 1991, Astron. Astrophys. Suppl, 91, pp409-424.

[6]   B.S. Carter, 1984, M.Sc. Thesis, University of Cape Town.

[7]   B.S. Carter, 1990, Mon. Not. R. Astron. Soc, 242, pp1-5.

[8]   M.M. Casali and T.J. Hawarden, 1992, The JCMT – UKIRT Newsletter, No. 4, pp33-35.

[9]   C.A. Christian, M. Adams, J.V. Barnes, H. Butcher, D.S. Hayes, J.R. Mould and M. Siegel, 1985, Publ. Astron. Soc. Pacific, 97, pp363-372.

[10]   M.J. Currie, 1998, SUN/102.4: HDSTRACE — Listing HDS Data Files (Starlink).

[11]   M.J. Currie and D.S. Berry, 2000, SUN/95.16: KAPPA — Kernel Application Package (Starlink).

[12]   M.J. Currie, G.J.Privett, A.J.Chipperfield, D.S. Berry and A.C. Davenhall, 2000, SUN/55.14: CONVERT — A Format-conversion Package (Starlink).

[13]   A.W.J. Cousins, 1976, Mem. R. Astron. Soc, 81, pp25-36.

[14]   A.W.J. Cousins, 1978, Mon. Notes Astron. Soc. South. Africa, 37 pp8-10.

[15]   G.S. DaCosta, 1990, CCDs in Astronomy, Astronomical Society of the Pacific Conference Series 8, pp326-334.

[16]   A.C. Davenhall, 2001, SUN/190.9: CURSA — Catalogue and Table Manipulation Applications (Starlink).

[17]   A.C. Davenhall and P.W. Draper, 2001, SC/17.1: The GAIA Cookbook (Starlink).

[18]   A.C. Davenhall, G.J. Privett and M.B. Taylor, 2001, SC/5.3: The 2-D CCD Data Reduction Cookbook (Starlink).

[19]   P.W. Draper, M.B. Taylor and A. Allan, 2000, SUN/139.13: CCDPACK — CCD data reduction package (Starlink).

[20]   P.W. Draper and N. Gray, 2000, SUN/214.8: GAIA — Graphical Astronomy and Image Analysis Tool (Starlink).

[21]   N. Eaton and B.K. McIlwrath, 2000, SUN/48.8: AGI — Applications Graphics Interface: A Subroutine Library for Accessing the Graphics Database (Starlink).

[22]   N. Eaton, P.W. Draper and A. Allan, 1999, SUN/45.10: PHOTOM — An Aperture Photometry Package (Starlink).

[23]   N. Eaton and G.J. Privett, 1996, SUN/42.5: DAOPHOT — Stellar Photometry Package (Starlink).

[24]   J.H. Elias, J.A. Frogel, A.R. Hyland and T.J. Jones, 1983, Astron. J, 88, pp1027-1030.

[25]   J.H. Elias, J.A. Frogel, K. Matthews and G. Neugebauer, 1982, Astron. J, 87 pp1029-1034 and erratum on p1893.

[26]   D. Engels, W.A. Sherwood, W. Wamsteker and G.V. Shultz, 1981, Astron. Astrophys. Suppl, 45, pp5-9.

[27]   M.C. Forbes, T. Banks, D.J. Sullivan, R.J. Dodd, A.C. Gilmore and P.M. Kilmartin, 1995, The Observatory, 115, No. 1124, pp29-30.

[28]   J.A. Frogel, S.E. Persson, M. Aaronson and K. Matthews, 1978, Astrophys. J, 220, pp75-97.

[29]   I.S. Glass, 1974, Mon. Notes Astron. Soc. South. Africa, 33, pp53-58 and errata on p71.

[30]   S.A. Graham, 1982, Publ. Astron. Soc. Pacific, 94, pp244-265.

[31]   R.M. Green, 1985, Spherical Astronomy (Cambridge University Press: Cambridge).

[32]   M. Golay, 1974, Introduction to Astronomical Photometry (D. Reidel: Dordrecht).

[33]   B. Grønbech, E.H. Olsen and B. Strömgren, 1976, Astron. Astrophys. Suppl, 26 pp155-176.

[34]   B. Grønbech and E.H. Olsen, 1977, Astron. Astrophys. Suppl, 25, pp213-270.

[35]   R.H. Hardie, 1962, ‘Photoelectric Reductions’, Chapter 8 of Astronomical Techniques, W.A. Hiltner (Ed), Stars and Stellar Systems, II (University of Chicago Press: Chicago), pp178-208.

[36]   W.E. Harris, W.P. Fitzgerald and B.C. Reed, 1981, Publ. Astron. Soc. Pacific, 93, pp507-517.

[37]   J.B. Hearnshaw, 1991, Southern Stars, 34, pp33-44.

[38]   A.A. Henden and R.H. Kaitchuck, 1990, Astronomical Photometry (Willmann-Bell: Richmond, Virginia). Originally published in 1982.

[39]   S.B. Howell (Ed), 1992, Astronomical CCD Observing and Reduction Techniques, Astronomical Society of the Pacific Conference Series 23.

[40]   C. Jaschek and M. Jaschek, 1987, The Classification of Stars (Cambridge University Press: Cambridge).

[41]   H.L. Johnson, 1964, Boletin de los Observatorios Tonantzintla y Tacubaya, 3, pp305-324.

[42]   H.L. Johnson, 1965, Comm. Lunar. Planet. Lab, No. 53 (Univ. Arizona) 3, pp73-77.

[43]   H.L. Johnson and W.W. Morgan, 1951, Astrophys. J, 114, pp522-543.

[44]   H.L. Johnson and W.W. Morgan, 1953, Astrophys. J, 117, pp313-352.

[45]   T.J. Jones and A.R. Hyland, 1982, Mon. Not. R. Astron. Soc, 200, pp509-520.

[46]   R.H. Kaitchuck, A.A. Henden and R. Truax, 1994, ‘Photometry in the Digital Age’, CCD Astronomy, 1, No. 3, pp20-23.

[47]   D.C. Kay and J.R. Levine, 1995, Graphics File Formats, second edition
(Windcrest/McGraw-Hill: New York). See in particular Chapter 18, pp235-244.

[48]   E. Krol, 1992, The Whole Internet User’s Guide and Catalog (O’Reilly and Associates Inc, Sebastopol, California).

[49]   E. Lamla, 1982, in Landolt-Börnstein, Zahlenwerte und Funktionen aus Naturwissenschaften und Technik, K. Schaifers and H.H. Voigt (Eds), VI/2b, Astronomie und Astrophysik (Springer-Verlag: Berlin).

[50]   A.U. Landolt, 1973, Astron. J, 78, pp959-981.

[51]   A.U. Landolt, 1983, Astron. J, 88, pp439-460.

[52]   A.U. Landolt, 1983, Astron. J, 88, pp853-866. Note that the stars listed in this paper are not necessarily suitable as general-purpose photometric standards and care should be exercised before using them as such. See the discussion in the paper for details.

[53]   A.U. Landolt, 1992, Astron. J, 104, pp340-371.

[54]   S.K. Leggett, 1992, Astrophys. J. Suppl, 82, pp351-394. In particular see pp357-358 for a discussion of photometric systems and the Appendix on pp391-393 for details of the transformations between them.

[55]   P. Massey, C.D. Garmany, M. Silkey and K. DeGioia-Eastwood, 1989, Astron. J, 97, pp107-130.

[56]   I.S. McLean, 1997, Electronic Imaging in Astronomy – Detectors and Instrumentation (Wiley: Chichester and New York). Published in association with Praxis in the Wiley-Praxis series in Astronomy and Astrophysics.

[57]   J.W. Menzies, R.M. Barfield, A.W.J. Cousins and J.D. Laing, 1989, SAAO Circular number 13.

[58]   J.W. Menzies, F. Marang, J.D. Laing, I.M. Coulson and C.A. Engelbrecht, 1991, Mon. Not. Roy. Astron. Soc., 248, pp642-652.

[59]   Th. Neckel, 1966, Z. für Astrophs, 63, pp221-241.

[60]   Th. Neckel and G. Klare, 1980, Astron. Astrophys. Suppl, 42, pp251-281.

[61]   J. Osborne, J.K. Ashley and G.J. Privett, 1996, SUN/146.3: OBSERVE — Check Star Observability (Starlink).

[62]   A.J. Penny, 1995, SUN/141.2: STARMAN — A Stellar Photometry and Image/Table Handling Package (Starlink).

[63]   G.J. Privett, 1998, SG/10.2: Preparing to Observe (Starlink).

[64]   R.E. Schild, 1977, Astron. J, 82, pp337-344.

[65]   Th. Schmidt-Kaler, 1982, in Landolt-Börnstein, Zahlenwerte und Funktionen aus Naturwissenschaften und Technik, K. Schaifers and H.H. Voigt (Eds), VI/2c, Astronomie und Astrophysik (Springer-Verlag: Berlin), p45.

[66]   D. A. Simons and A. Tokunaga, 2002, Publ. Astron. Soc. Pacific, 114, 169

[67]   Chr. Sterken and J. Manfroid, 1992, Astronomical Photometry — A Guide (Kluwer Academic Publishers: Dordrecht).

[68]   P.B. Stetson, 1987, Publ. Astron. Soc. Pacific, 99, pp191-222.

[69]   P.B. Stetson and W.E. Harris, 1988, Astron. J, 96, pp909-975.

[70]   V. Straižys, 1992, Multicolor Stellar Photometry, Pachart Astronomy and Astrophysics Series 15 (Pachart: Tucson).

[71]   B. Strömgren, 1963, Q. J. Roy. Astron. Soc., 4, pp8-36.

[72]   B. Strömgren, 1966, Annu. Rev. Astron. Astrophys (Annual Reviews Inc: Palo Alto, California), 4, pp433-472.

[73]   M. Tapia, L. Neri and M. Roth, 1986, Rev. Mexicana Astron. Astrofisica, 13, pp115-118.

[74]   A. Unsöld, 1967, The New Cosmos (Longmans and Springer-Verlag: New York), translated by W.H. McCrea. Originally published in German as Der neue Kosmos.

[75]   P.T. Wallace, 2000, SUN/67.51: SLALIB — Positional Astronomy Library (Starlink).

[76]   W. Wamsteker, 1981, Astron. Astrophys, 97, pp329-333.

[77]   R.F. Warren-Smith, 2000, SUN/33.7: NDF — Routines for Accessing the Extensible N-Dimensional Data Format (Starlink).

[78]   R.F. Warren-Smith and M.D. Lawden, 1999, SUN/92.11: HDS — Hierarchical Data System (Starlink).

[79]   D.C. Wells, E.W. Greisen and R.H. Harten, 1981, Astron. Astrophys. Suppl, 44, pp363-370.

[80]   A.T. Young and W.M. Irvine, 1967, Astron. J, 72, pp945-950.

[81]   M.V. Zombeck, 1990, Handbook of Space Astronomy and Astrophysics (Cambridge University press: Cambridge).