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HST-WFPC2 synthetic photometry has been computed from the passbands described in the `` WFPC2 Instrument Handbook''. We used the function responses[*] from May 1998 which include the effects of all the detection chain (filter transmission, CCD quantum efficiency, etc.), hence allowing direct comparisons of our synthetic c-m diagrams with HST data. The WFPC2 zero-points are usually defined on the system, based on a constant-flux-density-per-unit-wavelength. The conversion between the system (based on the Vega's spectrum) and the system is given by the following formula: which, with our passband definitions and the Vega model spectrum of Kurucz, give the colour differences, , , , and for F336W-F439W, F439W-F555W, F555W-F675W, and F675W-F814W respectively.

Colour-temperature and bolometric corrections using both the Lejeune et al. (1997) models and the Bessell et al. (1998) models have been presented by Origlia & Leitherer (2000). This paper also includes HST-NICMOS photometry and information on the transformation between WFPC2 and NICMOS and other systems.

Thibault Lejeune