Colour Transformations between BVRc and g′r′i′ Photometric Systems for Giant Stars

The transformation equations from BVRc to g ' r ' i ' magnitudes and vice versa for the giants were established from a sample of 80 stars collected from Soubiran et al. (2010) with confirmed surface gravity (2 <= log g (cm s(-2)) <= 3) at effective temperatures 4000 < T-eff(K) < 16000. The photometric observations, all sample stars at g ' r ' i ' and 65 of them at BVRc, were obtained at TUBITAK National Observatory (TUG) 1m (T100) telescope, on the Taurus Mountains in Turkey. The M-V absolute magnitudes of the giant stars were estimated from the absolute magnitude-temperature data for the giant stars by Sung et al. (2013) using the T-eff from the intrinsic colours considered in this study. The transformation equations could be considered to be valid through the ranges of the following magnitudes and colours involved: 7.10 < V-0 < 14.50, 7.30 < g(0)' < 14.85, -0.20 < (B -V)(0) < 1.41, -0.11 < (V -R-c)(0) < 0.73, -0.42 < (g' - r')(0) < 1.15, and -0.37 < (r' - i')(0) < 0.47 mag. The transformations were successfully applied to the synthetic BVRc data of 427 field giants in order to obtain the g ' r ' i ' magnitudes and colours. Comparisons of these data with the g ' r ' i ' observations of giants in this study show that the mean residuals and standard deviations lie within [-0.010, 0.042] and [ 0.028, 0.068] mag, respectively.