Low-resolution Spectroscopy for the Globular Clusters with Signs of
  Supernova Enrichment: M22, NGC 1851 and NGC 288
  There is increasing evidence for the presence of multiple red giant branches
(RGBs) in the color-magnitude diagrams of massive globular clusters (GCs). In
order to investigate the origin of this split on the RGB, we have performed new
narrow-band Ca photometry and low-resolution spectroscopy for M22, NGC 1851,
and NGC 288. We find significant differences (more than 4 sigma) in calcium
abundance from the spectroscopic HK' index for M22 and NGC 1851. We also find
more than 8 sigma differences in CN band strength between the Ca-strong and
Ca-weak subpopulations for these GCs. For NGC 288, however, a large difference
is detected only in the CN strength. The calcium abundances of RGB stars in
this GC are identical to within the errors. This is consistent with the
conclusion from our new Ca photometry, where the RGB splits are confirmed in
M22 and NGC 1851, but not in NGC 288. We also find interesting differences in
CN-CH correlations among these GCs. While CN and CH are anti-correlated in NGC
288, they show positive correlation in M22. NGC 1851, however, shows no
difference in CH between the two groups of stars with different CN strengths.
We suggest that all of these systematic differences would be best explained by
how strongly type II supernovae enrichment has contributed to the chemical
evolution of these GCs.
