We use Hubble Space Telescope (HST) and ground-based imaging to study the multiple populations of 47 Tuc, combining high-precision photometry with

DAOSPEC is a Fortran code for measuring equivalent widths of absorption lines in stellar spectra with minimal human involvement. It works with standard FITS format files and it is designed for use with high resolution (R>15000) and high signal-to-noise-ratio (S/N>30) spectra that have been binned on a linear wavelength scale. First, we review the analysis procedures that are usually employed in the literature. Next, we discuss the principles underlying DAOSPEC and point out similarities and differences with respect to conventional measurement techniques. Then experiments with artificial and real spectra are discussed to illustrate the capabilities and limitations of DAOSPEC, with special attention given to the issues of continuum placement; radial velocities; and the effects of strong lines and line crowding. Finally, quantitative comparisons with other codes and with results from the literature are also presented.

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. ...

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