J/A+A/573/A13 Metal abundances in 6 globular cluster (Dias+, 2015) FORS2/VLT survey of Milky Way globular clusters. I. Description of the method for derivation of metal abundances in the optical and application to NGC 6528, NGC 6553, M 71, NGC 6558, NGC 6426, and Terzan 8. Dias B., Barbuy B., Saviane I., Held E.V., Da Costa G.S., Ortolani S., Vasquez S., Gullieuszik M., Katz D. =2015A&A...573A..13D ADC_Keywords: Clusters, globular ; Abundances ; Effective temperatures Keywords: stars: abundances - stars: kinematics and dynamics - stars: Population II - globular clusters: general - Galaxy: stellar content Abstract: We have observed almost one third of the globular clusters in the Milky Way, targeting distant and/or highly reddened objects, as well as a few reference clusters. A large sample of red giant stars was observed with FORS2 at VLT/ESO at R∼2000. The method for deriving stellar parameters is presented with application to six reference clusters. We aim at deriving the stellar parameters effective temperature, gravity, metallicity, and α-element enhancement as well as the radial velocity to confirm the membership of individual stars in each cluster. We analyse the spectra collected for the reference globular clusters NGC 6528 ([Fe/H]~-0.1), NGC 6553 ([Fe/H]~-0.2), M 71 ([Fe/H]~-0.8), NGC 6558 ([Fe/H]~-1.0), NGC 6426 ([Fe/H]~-2.1), and Terzan 8 ([Fe/H]~-2.2). They cover the full range of globular cluster metallicities, and are located in the bulge, disc, and halo. Full spectrum-fitting techniques were applied by comparing each target spectrum with a stellar library in the optical region at 4560-5860Å. We employed the library of observed spectra MILES, and the Coelho synthetic library. We validated the method by recovering the known atmospheric parameters for 49 well-studied stars that cover a wide range in the parameter space. We adopted as final stellar parameters (effective temperatures, gravities, metallicities) the average of results using the observed and synthetic spectral libraries. Description: We observed with FORS2 at VLT/ESO 17 red giant stars in the globular cluster NGC 6528, 17 in NGC 6553, 12 in M 71, 17 in NGC 6558, 10 in NGC 6426, and 13 in Terzan 8, under projects 077.D-0775(A) and 089.D-0493(B). File Summary: FileName Lrecl Records Explanations ReadMe 80 . This file table3.dat 80 86 Star-by-star coordinates, magnitude, colour, heliocentric radial velocity, and membership selection table6.dat 127 86 Atmospheric parameters for all stars analysed in the six clusters: Teff, log(g), [Fe/H], [Mg/Fe], and [α/Fe] Byte-by-byte Description of file: table3.dat Bytes Format Units Label Explanations 1- 11 A11 --- Star Star identification (1) 13- 29 F17.13 deg RAdeg Right ascension (J2000) 31- 47 F17.13 deg DEdeg Declination (J2000) 49- 54 F6.3 mag Vmag V magnitude 56- 60 F5.3 mag V-I V-I colour index 62- 68 F7.2 km/s HV [-317/200] Heliocentric velocity 70- 78 F9.4 km/s HVt [231/209]? Ca triplet heliocentric velocity (2) 80 A1 --- Mmb [M] Membership (M=member) Note (1): Star identification as NGC NNNN_NN, M71_NN, Terzan8_NN and NGC NNNN_NN for NGC 6426, 6528, 6553 and 6558. Note (2): The velocities from CaT were taken from from Saviane et al. (2012A&A...540A..27S, Cat. J/A+A/540/A27) for NGC 6528, NGC 6553, M 71, and NGC 6558, and from Vasquez et al. (in prep.) for NGC 6426 and Terzan 8. Byte-by-byte Description of file: table6.dat Bytes Format Units Label Explanations 1- 11 A11 --- Star Star designation 13- 16 I4 K Teffa Effective temperature from MILES library 18- 20 I3 K e_Teffa rms uncertainty on Teffa 22- 25 I4 K Teffb Effective temperature from Coelho library 27- 29 I3 K e_Teffb rms uncertainty on Teffb 31- 34 I4 K Teff Average of MILES and Coelho effective temperature 36- 38 I3 K e_Teff rms uncertainty on Teff 40- 43 F4.2 [cm/s2] logga Surface gravity from MILES library 45- 48 F4.2 [cm/s2] e_logga rms uncertainty on logga 50- 53 F4.2 [cm/s2] loggb Surface gravity from Coelho library 55- 58 F4.2 [cm/s2] e_loggb rms uncertainty on loggb 60- 63 F4.2 [cm/s2] logg Average of MILES and Coelho surface gravity 65- 68 F4.2 [cm/s2] e_logg rms uncertainty on logg 70- 75 F6.3 [Sun] [Fe/H]a Metallicity from MILES library 77- 81 F5.3 [Sun] e_[Fe/H]a rms uncertainty on [Fe/H]a 83- 87 F5.2 [Sun] [Fe/H]b Metallicity from Coelho library 89- 92 F4.2 [Sun] e_[Fe/H]b rms uncertainty on [Fe/H]b 94- 98 F5.2 [Sun] [Fe/H] Average of MILES and Coelho metallicity 100-103 F4.2 [Sun] e_[Fe/H] rms uncertainty on [Fe/H] 105-110 F6.3 [Sun] [Mg/Fe] Abundance [Mg/Fe] from MILES library 112-115 F4.2 [Sun] e_[Mg/Fe] rms uncertainty on [Mg/Fe] 117-120 F4.2 [Sun] [a/Fe] Abundance [α/Fe] from Coelho library 122-125 F4.2 [Sun] e_[a/Fe] rms uncertainty on [α/Fe] 127 A1 --- Mmb [M] Membership (as in table3.dat) History: From electronic version of the journal (End) Patricia Vannier [CDS] 06-Feb-2015