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Milky Way globular clusters are excellent laboratories for stellar population detailed analysis that can be applied to extragalactic environments with the advent of the 40m-class telescopes like the ELT. The globular cluster population traces the early evolution of the Milky Way which is the field of Galactic archaeology. We present our GlObular clusTer Homogeneous Abundance Measurement (GOTHAM) survey. We derived radial velocities, Teff, log(g), [Fe/H], [Mg/Fe] for red giant stars in one third of all Galactic globular clusters that represent well the Milky Way globular cluster system in terms of metallicity, mass, reddening, and distance. Our method is based on low-resolution spectroscopy and is intrinsically reddening free and efficient even for faint stars. Our [Fe/H] determinations agree with high-resolution results to within 0.08 dex. The GOTHAM survey provides a new metallicity scale for Galactic globular clusters with a significant update of metallicities higher than [Fe/H] > -0.7. We show that the trend of [Mg/Fe] with metallicity is not constant as previously found, because now we have more metal-rich clusters. Moreover, peculiar clusters whose [Mg/Fe] does not match Galactic stars for a given metallicity are discussed. We also measured the CaII triplet index for all stars and we show that the different chemical evolution of Milky Way open clusters, field stars, and globular clusters implies different calibrations of calcium triplet to metallicity.
NGC 205 is a small galaxy (M/M⊙ = 0.7 × 109; MV = −16.6) currently located 36′ NW of M31. It is classified as dE because in ground-based images it appears as an elliptical body. However past investigations have revealed characteristics that are more typical of a disk galaxy: the specific frequency of globular clusters is 1.8; the large scale dynamics shows partial rotational support; there is a significant amount (106M⊙) of rotating gas (molecular and atomic) and dust; the central regions harbor a fairly complex stellar population, including a 100–500 Myr old nucleus surrounded by 50- and 100-Myr old stellar associations (see references in Monaco et al. 2009; M09). Very recently, thanks to hst/acs imaging we have been able to reveal a young central ‘field’ population (M09), extending out to ~40″ in radius (~160 pc). The luminosity function of the main sequence can be fitted with Saviane et al. (2004) model of continuous star formation (SF) from at least ~600 Myr ago to ~60 Myr ago. We found that 1.5 × 105M⊙ in stars were produced from ~300 Myr to ~60 Myr ago, with a SF rate of 7 × 10−4M⊙ yr−1. A continuous SF seems to support the latest simulations of NGC 205 orbit: Howley et al. (2008) found that the galaxy must be moving with a velocity 300–500 km s−1 (comparable to the escape velocity) along an almost radial orbit, and it should be approaching M31 for the first time. An episodic SF triggered by passages through M31 disk every ~300 Myr in a bound orbit (Cepa & Beckman 1988) is excluded by our data.
We report on the recent developments of our long-term investigation of the near-IR luminosity-metallicity relation for dwarf irregular galaxies in nearby groups. A very well-defined relation is emerging from our observational database, and a preliminary discussion of its implications is given.
We briefly describe our on-going investigation of the near-IR luminosity-metallicity relationship for dwarf irregular galaxies in nearby groups of galaxies. The motivations of the project and the observational databases are introduced, and a preliminary result is presented. The 12 + log(O/H) vs. H plane must be populated with more low-luminosity galaxies before a definite conclusion can be drawn.
We present deep V, I photometry of the globular cluster Terzan 7, a probable member of the globular cluster system of the Sagittarius dwarf spheroidal galaxy. The metallicity, estimated from a new method based on analytic RGB fits, agrees with previous estimates based on color-magnitude diagrams ([Fe/H]= −0.9 ± 0.1 dex). This result confirms a discrepancy between photometric and spectroscopic determinations. Using both the horizontal and vertical methods to estimate relative ages, we confirm that the age of Terzan 7 is about 70% that of 47 Tuc. A rich population of blue stragglers is found, strongly concentrated toward the center of the cluster.
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