Md. Shetrone et Mj. Keane, Spectral comparison of red giants in the second-parameter globular clusterpair NGC 288 and NGC 362, ASTRONOM J, 119(2), 2000, pp. 840-850
Abundances for 13 giants in the blue horizontal branch cluster NGC 288 and
12 giants in the red horizontal branch cluster NGC 362 are presented. The o
verall metallicities are found to be [Fe/H] = - 1.39 +/- 0.01 and -1.33 +/-
0.01 for NGC 288 and NGC 362, respectively. [alpha/Fe] ratios for the two
clusters are found to be nearly identical, although NGC 362 is found to hav
e a 0.1 dex smaller [Ca/Fe] abundance. Contrary to previous investigations,
oxygen-poor giants are found in both clusters. Although Na-O, Al-O anticor
relations are found in both clusters, zero-point and slope differences in t
he anticorrelations are found. These differences are attributed to ab initi
o higher O, Na, and Al abundances in NGC 288. Although the "mixed" giants i
n NGC 362 have significantly lower [O/Fe] ratios than those found in NGC 28
8, the extent of mixing is nearly equal in the two clusters because of this
ab initio abundance difference. No significant difference is found in the
r-process element Eu between the two clusters; however, the average Ba abun
dance, an s-process element, is slightly higher in NGC 288 than in NGC 362.
Mass-loss indicators Ha and Na core velocities show little difference from
previous investigations of other globular clusters. Excessive mass loss an
d deep mixing induced surface He abundance differences are ruled out as sou
rces of the difference in horizontal-branch morphology for these two cluste
rs.