On the giant, horizontal and asymptotic branches of Galactic globular clusters – V. CCD photometry of NGC 1261 ⋆

Abstract

BV CCD photometry is presented for 3352 stars (18 variables) in the globular cluster NGC 1261. The main conclusions drawn from the structure of the colour-magnitude diagram (CMD) are as follows. (i) The location and structure of the main branches agree with those found in previous studies, confirming the existence of a well-defined blue horizontal branch (ii) tail in addition to the large number of red HB stars. (iii) The mean metallicity derived from CMD indicators calibrated with the Zinn & West scale is [Fe/H]=−1.4±0.2, and the very small intrinsic width of the various branches yields very low upper limits (Δ[Fe/H]≤0.06, Δ[CNO]≤0.2) for any chemical abundance spread. (iii) The RGB bump is detected at V=16.70±0.05 as a clump of stars in the luminosity function of the red giant branch