GOTHAM survey: MilkyWay globular cluster chemical evolution based on full spectrum fitting

B. Dias1*, B. Barbuy2, I. Saviane1, E. V. Held3, G. S. Da Costa4, S. Ortolani3,5, and M. Gullieuszik3
1European Southern Observatory, Alonso de Cordova 3107, Santiago, Chile
2USP, Dept. de Astronomia, Rua do Matão 1226, São Paulo 05508-090, Brazil
3INAF, Osservatorio Astronomico di Padova, Vicolo dell’Osservatorio 5, 35122 Padova, Italy
4Research School of Astronomy & Astrophysics, Australian National University, Mount Stromlo Observatory, via Cotter Road, Weston Creek, ACT 2611, Australia
5Università di Padova, Dipartimento di Astronomia, Vicolo dell’Osservatorio 2, 35122 Padova, Italy

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Milky Way globular clusters are excellent laboratories for detailed analyses of stellar populations and which can be applied to extragalactic environments. We use our GlObular clusTer Homogeneous Abundance Measurement (GOTHAM) survey to show how much the chemical abundances of globular cluster stars differ from field stars, open clusters, and extragalactic star clusters. In particular, we show how [α/Fe] a ects the calibration of the calcium triplet to metallicity according to the chemical evolution history of the host galaxy (Vasquez et al. in prep.), and we conclude that there is no universal calibration for the calcium triplet index. We apply full spectrum fitting techniques using synthetic and empirical stellar spectral libraries. This method is intrinsically reddening-free and ecient even for faint stars and low-resolution spectroscopy, and we use it to derive radial velocity, Teff, log(g), [Fe/H], [Mg/Fe], and [α/Fe]. We obtained results for [Fe/H] that were within 0.08 dex of the results from highresolution spectroscopy (Dias et al. 2015, 2016), with an improvement for the metal-rich regime, which makes our results establish a new metallicity scale for Galactic globular clusters. Our technique is fully suitable for observing extragalactic globular cluster stars with 40m-class telescopes like the E-ELT.

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Keywords : stars: abundances – stars: kinematics and dynamics – stars: population II – galaxy: globular clusters – galaxy: stellar content – galaxy: evolution - galaxy: formation – galaxy: bulge – galaxy: halo