Metallicity and absolute magnitude calibrations for UBV photometry

Abstract

Calibrations are presented here for metallicity ([Fe/H]) in terms of the ultraviolet excess, [delta(U - B) at B - V = 0.6, hereafter delta(0.6)], and also for the absolute visual magnitude (M-v) and its difference with respect to the Hyades (Delta M-V(H)) in terms of delta(0.6) and (B - V), making use of high-resolution spectroscopic abundances from the literature and Hipparcos parallaxes. The relation [Fe/H]-delta(0.6) has been derived for dwarf plus turn-off stars, and also for dwarf, turn-off, plus subgiant stars classified using the M-V-(B - V)(0) plane of Fig. 11, which is calibrated with isochrones from Bergbusch & VandenBerg (and also VandenBerg & Clem). The [Fe/H]-delta(0.6) relations in our equations (5) and (6) agree well with those of Carney, as can be seen from Fig. 5(a). Within the uncertainties, the zero-points, +0.13(+/- 0.05) of equation (5) and +0.13(+/- 0.04) of equation (6), are in good agreement with the photometric ones of Cameron and of Carney, and close to the spectroscopic ones of Cayrel et al. and of Boesgaard & Friel for the Hyades open cluster. Good quantitative agreement between our estimated [Fe/H] abundances with those from uvby-beta photometry and spectroscopic [Fe/H](spec) values demonstrates that our equation (6) can be used in deriving quality photometric metal abundances for field stars and clusters using UBV data from various photometric surveys.