Spectral comparison of red giants in the second-parameter globular clusterpair NGC 288 and NGC 362

Citation
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
Citations number
57
Categorie Soggetti
Space Sciences
Journal title
ASTRONOMICAL JOURNAL
ISSN journal
00046256 → ACNP
Volume
119
Issue
2
Year of publication
2000
Pages
840 - 850
Database
ISI
SICI code
0004-6256(200002)119:2<840:SCORGI>2.0.ZU;2-5
Abstract
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.