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Globular clusters (GCs) provide statistically significant coeval populations of stars spanning various evolutionary stages, allowing robust constraints on stellar evolution model parameters and ages. We analyze eight old Milky Way GCs with…

One of the largest sources of uncertainty in the computation of globular cluster isochrones and hence in the age determination of globular clusters is the lack of a rigorous description of convection. Therefore, we calibrated the…

We present spectroscopic ages, metallicities, and [alpha/Fe] ratios for 70 globular clusters in M31 that were derived from Lick line-index measurements. In addition to a population of old (>10 Gyr) globular clusters with a wide range of…

We use nearby K dwarf stars to measure the helium-to-metal enrichment ratio, a diagnostic of the chemical history of the Solar Neighbourhood. Our sample of K dwarfs has homogeneously determined effective temperatures, bolometric…

We supplement recent evolutionary computations of canonical stellar models (i.e. with inefficient core overshooting) with Z=0.0002, 0.0004, 0.0006, 0.001, 0.004, 0.008 and suitable assumptions about the original He content. Evolutionary…

We derive ages, metallicities and [alpha/Fe] ratios from the integrated spectra of 23 globular clusters in M31, by employing multivariate fits to two stellar population models. In parallel we analyze spectra of 21 Galactic globular clusters…

We show that the factor $\sim$2 discrepancy between spectroscopic and photometric age determinations of the Galactic bulge main-sequence turnoff can be naturally explained by positing an elevated helium enrichment for the bulge relative to…

We present updated stellar population models appropriate for old ages (>1 Gyr) and covering a wide range in metallicities (-1.5<[Fe/H]<0.3). These models predict the full spectral variation associated with individual element abundance…

We test the performance of our analysis technique for integrated-light spectra by applying it to seven well-studied Galactic GCs that span a wide range of metallicities. Integrated-light spectra were obtained by scanning the slit of the…

An extensive grid of metal-rich isochrones utilizing the latest available input physics has been calculated for comparison with the old, metal-rich open cluster NGC 6791. The isochrones have been simultaneously fit to BV and VI color…

We present isochrone ages and initial bulk metallicities ($\rm [Fe/H]_{bulk}$, by accounting for diffusion) of 163,722 stars from the GALAH Data Release 2, mainly composed of main sequence turn-off stars and subgiants ($\rm 7000…

Using data from the GALAH survey, we explore the dependence of elemental abundances on stellar age and metallicity among Galactic disc stars. We find that the abundance of most elements can be predicted from age and [Fe/H] with an intrinsic…

The Yale stellar evolution code has been modified to use the OPAL equation of state tables (Rogers 1994). Stellar models and isochrones were constructed for low metallicity systems ($-2.8 \le [Fe/H] \le -0.6$). Above $M\sim 0.7\,\msun$, the…

In Papers I and II of this series, the existence of two distinct halo populations of stars have been found in the solar neighborhood. Precise relative ages and orbital parameters are determined for 67 halo and 16 thick-disk stars having…

In the era of large spectroscopic surveys, massive databases of high-quality spectra provide tools to outline a new picture of our Galaxy. In this framework, an important piece of information is provided by our ability to infer stellar…

We extend to lower metallicities recent evolutionary computations devoted to Magellanic Clouds stars, presenting and discussing new stellar models with Z=0.0002, 0.0004, 0.0006, 0.001 and suitable assumptions about the original He content.…

Solar twins are stars with similar stellar (surface) parameters to the Sun that can have a wide range of ages. This provide an opportunity to analyze the variation of their chemical abundances with age. Nissen (2015) recently suggested that…

Helium and hydrogen recombination lines observed in low-metallicity, extragalactic, HII regions provide the data used to infer the primordial helium mass fraction, Y_P. In deriving abundances from observations, the correction for unseen…

We introduce the Yale-Potsdam Stellar Isochrones (YaPSI), a new grid of stellar evolution tracks and isochrones of solar-scaled composition. In an effort to improve the Yonsei-Yale database, special emphasis is placed on the construction of…

Using the optimal sampling model, we synthesized the embedded clusters of ATLASGAL clumps with HII regions (HII-clumps). The 0.1 Myr isochrone was used to estimate the bolometric luminosity of each star in an embedded cluster, we also added…