INVESTIGADORES
PIATTI Andres Eduardo
artículos
Título:
Lower metallicity of the Galactic globular cluster system: Calcium triplet spectroscopy of metal-poor globular cluster giants
Autor/es:
GEISLER, DOUG; PIATTI, ANDRÉS E.; CLARIA OLMEDO, JUAN JOSÉ; MINNITI, DANTE
Revista:
ASTRONOMICAL JOURNAL
Referencias:
Año: 1995 vol. 109 p. 605 - 617
ISSN:
0004-6256
Resumen:
Medium-resolution spectra at the Ca II infrared triplet are presented
for 164 giants in 12 metal-poor Galactic globular clusters. The data for
4 for these clusters are combined with published data for 7 other
clusters with well-known metal abundances and used to calibrate the
derivation of metallicity values for the remaining clusters from the
summed strength of the 2 strongest Ca lines at a given V -
VHB. The mean (Fe/H) values we find are: -1.82 for NGC 2298,
-2.10 for NGC 4372, -1.84 for NGC 4833, -2.10 for NGC 5053, -1.87 for
NGC 5694, -1.94 for NGC 5897, -1.86 for NGC 6101 and -1.86 for NGC 6144,
with a typical mean error of 0.05 dex from an average of 10 member
giants per cluster. Upper limits to any intrinsic intracluster
metallicity dispersion are less than or = 0.05 dex in all of the
clusters except approximately 0.15 dex in NGC 5053 and NGC 5694, where
the higher limits are due to the lower quality spectra for these more
distant clusters. The mean metallicity values for most of the program
clusters are in excellent agreement with the Zinn scale, while those for
NGC 5897 and NGC 5053 are 0.26 dex lower and 0.48 dex higher than given
by Zinn, respectively. The value for NGC 5897 is intermediate to that
given by the Washington photometry of Geisler et al. (1992b) and Zinn.
The high value for NGC 5053 increases the already very significant
difference between the metallicity distribution functions of halo
clusters and field stars. Our results, combined with previous
determinations for other clusters, indicate that the lower metallicity
limit for globular clusters in the Galaxy is -2.25 +/- 0.10. A similar
value also appears to hold for other nearby globular cluster systems. We
also derive mean cluster radial velocities to a typical precision of 1.2
km/s (mean error). The values for several of the program clusters are
significantly different from previously published values. An updated
analysis slightly strengthens van den Bergh's (1993) finding that halo
clusters on retrograde orbits have different horizontal branch
morphologies than clusters on prograde orbits.