SECONDARY CALIBRATORS AT SUBMILLIMETER WAVELENGTHS

This paper is the first attempt to establish a set of secondary calibrators for submillimetre continuum photometry. In total we include photometry on 21 sources (ultracompact H II regions, compact bipolar outflow sources and protoplanetaries). These sources are all calibrated relative to Mars and Uranus, which are the primary submillimetre standards. Data are given for all the major atmospheric windows in the (sub)millimetre regime for a standard set of broad-band filters used in the common-user bolometer UKT14, i.e. 2, 1.3 and 1.1 mm, and 800, 450 and 350 mum. For most sources, some data are also given for the two narrow-band filters at 850 and 750 mum, which split up the 800-mum window. For some sources we have about 20 independent observations spread over a period of about 2 years. The standard deviations of the data show that we typically achieve an accuracy of a few per cent at 1 mm, and about 10-15 per cent at 450 and 350 mum. The errors do not include the uncertainties in the absolute flux densities of the planets, which add an additional 5-10 per cent in total errors. Although these calibrators are mainly intended for use on the James Clerk Maxwell Telescope (JCMT), the list should also be applicable to other telescopes. At JCMT, the present calibrator set has already been in use for about 2 years.