Reddening estimation for halo red giants using UVBY photometry

Abstract

Updated uvby observations for a larger sample of metal-deficient red giants are presented and combined with a select sample of data from the literature transformed to a common system. Using the reddening maps of Burstein &amp; Heiles (1982), new absolute magnitudes, distances, metallicities, and reddenings are derived for each star. The metallicities are determined with a revised calibration of the m<SUB>1</SUB>, (b-y) diagram based upon comparison to a complilation of recent spectrsoscopic abundances transformed to a common system. The photometric abundances agree very well with the spectroscopic; the dispersion among the residuals for 58 giants is +/- 0.16 dex. The dereddened indices are used to show that for red giants with (Fe/H) less than -1.5, there is a well-defined relation in the c<SUB>0</SUB>, (b-y)<SUB>0</SUB> diagram which exhibits only a weak dependence upon metallicity. Use of the standard relations allows one to obtain reddening estimates for normal halo field giants and globular clusters in the appropriate metallicity range.