SCUBA secondary calibrators

This webpage provides our detailed analysis of the secondary calibrators, and suggests the values for use in their reduction as calibrators. FOR USE DURING OBSERVING, we suggest you go to our Calibration Cookbook, which gives a quick guide to the details below as well as further advice. Older versions of this webpage can be found here (2002-2003 version) and here (1998-2001 version).

Current secondary calibrators

The primary flux calibration of SCUBA data is based on the planets Mars, Uranus and Neptune, but at some times of the night and year these may be unavailable. A (very) small set of 'secondary' calibrators has been collated from a variety of sources to use during these times, but these are few and far between and most of them are not ideal!

The values below were obtained for a new analysis of observations between April 1st 2000 and September 30th 2003, with the exception of the variable calibrators OH 231.8 and IRC+10216, for which the complete data sets have been used from 1997 - 2003. The values are all in agreement with our previous values, derived from (usually fewer) observations between 1997 and 2001. Wherever possible, only observations with 120" chop throws have been used in this analysis. For the variable calibrators, use the links in the table below to see the updated curves.

For each source, two flux estimates are given at each wavelength. The first is the peak flux, in Jy/beam, which can be used for unresolved sources and also for photometry observations (see this note for guidance). The second is the integrated flux within a circular aperture with 20" radius, in Jy/aperture, which should be used for resolved sources (see this paper by Jenness et al. for a more in-depth discussion on this issue).

The previous version of this document supplied fluxes for OH 231.8 and IRC 10216 at 450 µm; however, later data does not support these numbers. The two sources are clearly variable at 850 µm and it is likely that they are at 450 µm also. However, the scatter in the data is too large to fit a curve to, and so if your only calibrator is one or both of these two sources, we suggest using the values from the monthly updates webpage instead.

The previous version of this document also supplied separate peak fluxes for photometry, pointing maps and general maps. However, we did not find a significant difference between these three data sets and so now a single value is given which can be used for all three observing modes.

Calibration has not been attempted at 350/750 micron, and very few 1350um data were available before the filter drum broke in 1999. However, numbers are still available upon request.

Future secondary calibrators?

Obviously, we would like more secondary calibrators to increase the accuracy of results from SCUBA. We have been attempting to locate candidate objects in our E&C program - thanks to all whose time has been interrupted by making these observations for us. A report on progress so far (June 2005) can be found here.