A comparison of the ROSAT WFC and EUVE source catalogues

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Abstract
The first all-sky surveys at extreme-ultraviolet (EUV) wavelengths have recently been carried out by the ROSAT Wide Field Camera (WFC, 1990-1991) and the EUV Explorer (EUVE, 1992-1993). We present a comparison of the WFC and EUVE all-sky survey results, concentrating on the correspondence between the two pairs of short-wavelength filters, operating in the band from ∼60 to ∼200 Å. Over 80 per cent of the EUVE 100-Å sources are detected by the WFC, whereas for the EUVE 200-A sources the fraction is as high as 93 per cent. Both surveys are dominated by late-type (F-M) stars and hot white dwarf stars, with cataclysmic variables (CVs), early-type stars and active galactic nuclei also contributing. We use the effective area versus wavelength calibrations of the various filters to predict count-rate ratios for various model spectra. By comparing these predictions with the measured ratios, we are able to define the range of spectral properties typical of the various classes of EUV source. The level of flux variability in the EUV band of late-type stars and CVs is also investigated.

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