Bj. Anthonytwarog et al., VBY H-BETA CCD PHOTOMETRY OF MELOTTE-66 - A DISK ANALOG OF OMEGA-CENTAURI, Publications of the Astronomical Society of the Pacific, 106(699), 1994, pp. 486-499
Citations number
54
Categorie Soggetti
Astronomy & Astrophysics
Journal title
Publications of the Astronomical Society of the Pacific
A CCD study of the peculiar open cluster, Melotte 66, on the nu by Hbe
ta system is presented. The V,(b-y) color-magnitude diagram of this me
tal-deficient, old disk cluster confirms the anomalous features found
in photographic BV studies and extends the main sequence to V=20. The
main sequence exhibits a (b - y) color range significantly larger than
expected from photometric errors alone; the (b - y) colors are correl
ated with Hbeta implying that the dispersion is real and is not the re
sult of variable reddening across the cluster. The m1 indices for the
turnoff stars imply a spread in [Fe/H] too small to explain the color
range. Though the subgiant region is poorly defined, the region above
the turnoff in the Hertzsprung gap is richly populated by a group of y
ellow stragglers whose membership is confirmed by radial star counts a
nd radial velocities. The giant branch is richly populated but shows a
smaller spread in color at a given V than one would expect from the t
urnoff region. More important, the giants exhibit a large scatter in m
1, in contradiction with the turnoff observations. Various explanation
s for these observations are discussed, including CN variations among
the giants triggered by either binary evolution or rapid rotation amon
g the main-sequence stars.