1996A&A...311..245F

We have made a comparative study of the Sun and solar analogue stars using the published solar ultraviolet fluxes and IUE low dispersion spectra of the solar analogues. The Hyades dwarf HD 28099 (vB64) shows a flux excess below 2500A which is probably due to chromospheric activity since it is a relatively young star. HD 44594, 186408 (16CygA) and 186427 (16CygB) all show very similar ultraviolet spectra to the Sun. From a comparison with Kurucz ATLAS9 models we find 16CygA and B to be metal-rich by 0.02±0.03dex with temperatures of 5790±20K and 5750±20K respectively, assuming a solar temperature of 5770K. These results are consistent with other recent work. For HD 44594 we find T_e=5760±20K and [M/H]=0.01±0.03 which is significantly less metal-rich than found in the recent work of Cayrel de Strobel & Bentolila (1989). We have also checked the ultraviolet absolute flux scale by comparing the ratio of the solar analogue fluxes to the solar flux at both optical and ultraviolet wavelengths. For 16CygA and B we find that, after normalising in the optical and using the ATLAS9 models to correct the ultraviolet fluxes of the solar analogues for their small metallicity excess, there is a discrepancy of 16(±4)% in the sense that the IUE absolute calibration gives fluxes that are too low or the absolute scale of the solar uv flux measurements is too high. This can be reduced to 6(±4)% if we firstly accept a 7% higher IUE absolute scale as suggested by independent evidence, and secondly use only the older solar ultraviolet flux measurements of Heath (1980) & Mentall et al. (1981) and ignore the more recent work of Labs et al. (1987). Finally we have inverted the problem and asked which of the three solar flux measurements (Heath, Mentall et al. or Labs et al.) fit better the slope of the ultraviolet continuum of the solar analogue IUE data. As with the absolute scale we find better agreement with the older measurements of Heath and Mentall et al. than with the more recent work of Labs et al.