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

Abstract

The transformation equations from $BV{R}_c$ to $g^{\prime }{r}^{\prime }{i}^{\prime }$ 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 ($2\le \log g$ (cms${}^{-2}$)$\le 3$) at effective temperatures $4000<T_{eff}(K)<16000$. The photometric observations, all sample stars at $g^{\prime }{r}^{\prime }{i}^{\prime }$ and 65 of them at $BV{R}_c$, were obtained at TÜBİTAK 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: $7.10<V_0<14.50$, $7.30<g_0^{\prime }<14.85$, $-0.20<(B-V{)}_0<1.41$, $-0.11<(V-R_c{)}_0<0.73$, $-0.42<(g^{\prime }-r^{\prime }{)}_0<1.15$, and $-0.37<(r^{\prime }-i^{\prime }{)}_0<0.47$ mag. The transformations were successfully applied to the synthetic $BV{R}_c$ data of 427 field giants in order to obtain the $g^{\prime }{r}^{\prime }{i}^{\prime }$ magnitudes and colours. Comparisons of these data with the $g^{\prime }{r}^{\prime }{i}^{\prime }$ 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.

16 pages, including 10 figures and 7 tables, accepted for publication in PASA