Galactic Globular Cluster Metallicity Scale from the CA II Triplet I. Catalog

Abstract

We have obtained 2640 CCD spectra with resolution ∼4Å in the region 7250-9000Å for 976 stars lying near the red giant branches in color-magnitude diagrams of 52 Galactic globular clusters. Radial velocities of ∼16 km s −1 accuracy per star determined from the spectra are combined with other criteria to assess quantitative membership probabilities. Measurements of the equivalent widths of the infrared 1 Visiting Astronomer, Las Campanas Observatory.-2calcium triplet lines yield a relative metal-abundance ranking with a precision that compares favorably to other techniques. Regressions between our system and those of others are derived. Our reduction procedures are discussed in detail, and the resultant catalog of derived velocities and equivalent widths is presented. The metal abundances derived from these data will be the subject of a future paper.provided numerous results of widespread interest, the original motivation of our program remains. In this paper we describe how we optimized our reduction of the spectral data ( §3) to provide radial velocities ( §4) and equivalent widths ( §5), compare our prescriptions and results with those of other workers ( §5.5), and present a catalog of the individual stellar results ( §7). Following the AD91 prescription, the cluster reduced equivalent widths, W ′ , are calculated ( §6). A companion paper discusses the calibration of our cluster W ′ values to [Fe/H] values, and the astrophysical implications of our results. ObservationsSpectra were obtained at the Las Campanas Observatory's 2.5m Dupont telescope equipped with the modular spectrograph and the Canon 85mm f/1.2 camera. A GG495 filter was used to block the second and higher spectral orders. The TI#2 detector (800 × 800 thinned CCD; readout noise = 11 e − pix −1 ; gain = 1.35 e − per ADU; scale = 0.85 ′′ pix −1 ) was used with an 831 l mm −1 (8000Å blaze) grating, which produced a dispersion of 2.19Å pix −1 and spectral coverage from 7250-9000Å. The 8 ′ × 1.25 ′′ slit provided an instrumental spectral resolution of ∼4Å.Observations were obtained on two 1989 runs: 1) April 13-20 and 2) July 13-21. Of the 52 clusters observed, 23 were observed during the first run only, 26 were observed during the second run only, and three were observed during both runs to check the consistency of our results. In each cluster, spectra were obtained for 10 to 20 stars selected from published color-magnitude diagrams (CMDs) to lie on the red giant branch (RGB) and, if proper motion data were available, to be likely proper-motion members. Probable asymptotic branch (AGB) stars were avoided, as were horizontal branch (HB) stars, and known variable stars near the RGB tip. Slit positions were chosen to contain at least two stars per spectrograph rotation.Each star was observed two or three times consecutively, with an Fe-Ar arc taken before and after each sequence for the wavelength calibration. Occasionally the same star was observed on different nights, or with a different slit orientation, to check for systematic effects in our results. ...

New constraints on the chemical evolution of the dwarf spheroidal galaxy Leo I from VLT spectroscopy

“…Two different exposure times were used (long and short exposure) to prevent saturation of the brightest RGB stars. The photometry of the GC stars was taken from the data compilation of Rutledge et al (1997b).…”

Integrated colours of Milky Way globular clusters and horizontal branch morphology

“…Where available, metallicities were compiled from the homogeneous data set of Rutledge et al (1997aRutledge et al ( , 1997b. They are based on the combined strengths of the λ8498, λ8542, and λ8662 Ca II triplet lines of red giant branch (RGB) stars that are probable GC members.…”

“…They are based on the combined strengths of the λ8498, λ8542, and λ8662 Ca II triplet lines of red giant branch (RGB) stars that are probable GC members. Rutledge et al (1997aRutledge et al ( , 1997b followed the techniques of Armandroff & Da Costa (1991) for measuring the equivalent widths of these lines, correcting them to a reference point on the RGB equal to the V magnitude of the horizontal branch, and correlating them against various [Fe/H] measurements. The metallicities given in column 5 of Table 2 of Rutledge et al (1997b) were adopted in this study, this column containing their "most probable" [Fe/H] value on the scale of Zinn & West (1984;ZW84).…”

“…The metallicities given in column 5 of Table 2 of Rutledge et al (1997b) were adopted in this study, this column containing their "most probable" [Fe/H] value on the scale of Zinn & West (1984;ZW84). Since the Rutledge et al (1997b) metallicities are based on spectroscopy of individual cluster red giants (typically ∼10-20 per cluster, Rutledge et al 1997a), they should not be subject to horizontal branch effects in the way that metallicity estimates based on integrated cluster-light techniques could be. Where not available from this source, values of [Fe/H] for the clusters in our compilation were adopted from Table 6 of ZW84. Reddenings for the clusters included in this study are available from both Reed et al (1988) and the 1999 version (designated elsewhere in this paper as H99) of the catalogue of Milky Way GC properties described by Harris (1996).…”

The Ca ii triplet in red giant spectra: [Fe/H] determinations and the role of [Ca/Fe]

“…As a result, measurements of the strength of these lines have been extensively used as a metallicity indicator in a variety of stellar systems. These include Galactic globular clusters (e.g., Armandroff & Da Costa 1991;Da Costa & Armandroff 1995;Rutledge et al 1997;Saviane et al 2012), Galactic open clusters (e.g., Cole et al 2004;Warren & Cole 2009;Carretta et al 2009;Carrera et al 2015) and stars in the Galactic Bulge (e.g., Vásquez et al 2015). It has also been used to study both field stars and star clusters in the LMC (e.g., Olszewski et al 1991;Cole et al 2005;Carrera et al 2008a) and SMC (e.g., Da Costa & Hatzidimitriou 1998;Carrera et al 2008b;Parisi et al 2010;Dobbie et al 2014;Parisi et al 2015), as well as red giants in dwarf spheroidal (e.g., Armandroff & Da Costa 1991;Pont et al 2004;Tolstoy et al 2004;Battaglia et al 2008Battaglia et al , 2011 and dwarf irregular galaxies (e.g., Leaman et al 2013).…”