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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.
We present the first results of a comprehensive HST study of the star-formation history of Fornax dSph, based on WFPC2 imaging of 7 Fornax fields. Our observations reach the oldest main-sequence turnoffs, allowing us to address fundamental questions of dwarf galaxy evolution, such as the spatial variations in the stellar content, and whether the old stellar population is made up of stars formed in a very early burst or the result of a more continuous star formation.
In spite of its relevance, the Thermally Pulsing Asymptotic Giant Branch (TP-AGB) phase is one of the most uncertain phases of stellar evolution, and a major source of disagreement between the results of different population synthesis models of galaxies. I will briefly review the existing literature on the subject, and recall the basic prescriptions that have been used to fix the contribution of TP-AGB stars to the integrated light of stellar populations. The simplicity of these prescriptions greatly contrasts with the richness of details provided by present-day databases of AGB stars in the Magellanic Clouds, which are now being extended to other nearby galaxies. I will present the first results of an ongoing study aimed at simulating photometry, chemistry, pulsation, mass loss, dust properties of AGB star populations in resolved and un-resolved galaxies. We test our predictions against observations from various surveys of the Magellanic Clouds (DENIS, 2MASS, OGLE, MACHO, Spitzer, and AKARI). I will discuss the implications and outline the plan of future developments.
Recent progress in our knowledge of stellar populations in local dwarf spheroidal galaxies is briefly discussed. A few results are summarized including wide field observations of stellar populations and their spatial variations, studies of AGB and variable stars, extension to near-infrared wavelengths, and the interpretation effort based on synthetic color-magnitude diagrams and chemical evolution models.
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.
Results are presented on a study of the short period variable stars in the dwarf irregular galaxy NGC 6822. We observed an almost uniformly populated classical instability strip from the Horizontal Branch up to the Classical Cepheid region. The main goal we achieved from the analysis of the faint sample is the first detection of RR Lyrae stars in this galaxy.
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.
We have obtained multislit spectroscopy of 40 known globular clusters in the nearby peculiar elliptical galaxy NGC 5128 at the ESO NTT telescope. Measurements of metal and hydrogen absorption line indices have been used to estimate the age and metal content of individual clusters. The results have been combined with previous data from multifibre spectroscopy of clusters in the halo of NGC 5128 to study the age and metallicity distribution of the globular cluster system.
It has recently been found that diffuse dwarf elliptical galaxies (dE), as well as low–luminosity normal ellipticals of relatively low surface–brightness, are supported by an anisotropic velocity distribution. New kinematic observations have been obtained of the dwarf elliptical galaxy NGC 185. The velocity dispersion is constant at 28 ± 8 km s–1 between 3″ and 40″, but may increase to about twice that value in the center. We find an upper limit of 10 km s–1 for the rotation along either axis, so that the velocity distribution is anisotropic. The derived M/LB is ~ 3 in solar units.
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