We present new theoretical period–luminosity (PL) and period–radius (PR) relations at multiple wavelengths (Johnson–Cousins–Glass and Gaia passbands) for a fine grid of BL Herculis models computed using mesa-rsp. The non-linear models were computed for periods typical of BL Her stars, i.e. 1 ≤ P(days) ≤ 4, covering a wide range of input parameters: metallicity (−2.0 dex ≤ [Fe/H] ≤ 0.0 dex), stellar mass (0.5–0.8 ), luminosity (50–300 ) and effective temperature (full extent of the instability strip; in steps of 50K). We investigate the impact of four sets of convection parameters on multi-wavelength properties. Most empirical relations match well with theoretical relations from the BL Her models computed using the four sets of convection parameters. No significant metallicity effects are seen in the PR relations. Another important result from our grid of BL Her models is that it supports combining PL relations of RR Lyrae and Type II Cepheids together as an alternative to classical Cepheids for the extragalactic distance scale calibration.

I present the first results of multiple stellar populations in globular clusters from James Webb Space Telescope (JWST) data. We obtained combined NIRSpec and NIRCam data of the GC 47 Tucanae to investigate the properties of the different stellar populations in the low-mass regime, down to ∼0.5 M⊙. Our analysis of both the photometric data and the spectra suggests that the multiple stellar populations among M dwarfs share similar properties of those extensively studied on bright red giant branch stars. The comparison between stellar populations’ properties at different stellar mass, e.g. at the red giants and M dwarfs’ phases, can potentially provide strong constraints to the formation scenarios of the still eluding phenomenon of the multiple populations in star clusters.

The investigation of the metal-poor tail in the Galactic bulge provides unique information on the early Milky Way assembly and evolution. A chemo-dynamical analysis of 17 very metal-poor stars (VMP, [Fe/H < – 2.0]) selected from the Pristine Inner Galaxy Survey was carried out based on Gemini/GRACES spectra. The chemistry suggests that the majority of our stars are very similar to metal-poor stars in the Galactic halo. Orbits calculated from Gaia EDR3 imply these stars are brought into the bulge during the earliest Galactic assembly. Most of our stars have large [Na,Ca/Mg] abundances, and thus show little evidence of enrichment by pair-instability supernovae. Two of our stars (P171457, P184700) have chemical abundances compatible with second-generation globular cluster stars, suggestive of the presence of ancient and now dissolved globular clusters in the inner Galaxy. One of them (P171457) is extremely metal-poor ([Fe/H < – 3.0]) and well below the metallicity floor of globular clusters, which supports the growing evidence for the existence of lower-metallicity globular clusters in the early Universe. A third star (P180956, [Fe/H]∼ – 2) has low [Na,Ca/Mg] and very low [Ba/Fe] for its metallicity, which are consistent with formation in a system polluted by only one or a few low-mass supernovae. Interestingly, its orbit is confined to the Galactic plane, like other very metal-poor stars found in the literature, which have been associated with the earliest building blocks of the Milky Way.

The chemo-dynamics of the stellar populations in the Galactic Bulge inform and constrain the Milky Way’s formation and evolution. The metal-poor population is particularly important in light of cosmological simulations, which predict that some of the oldest stars in the Galaxy now reside in its center. The metal-poor bulge appears to consist of multiple stellar populations that require chemo-dynamical analyses to disentangle. In this paper, I describe the detailed chemo-dynamical study of the metal-poor stars in the inner Galaxy, named The COMBS Survey which uses VLT/FLAMES spectra of 350 metal-poor stars. I discuss the results and the implications for early Milky Way formation and chemical evolution. In addition, I preview results from an ongoing survey of carbon-enhanced metal-poor stars, which are thought to be solely enriched by the first generation of stars.

I present the first evidence of multiple populations in the globular cluster (GCs) 47 Tucanae based on images collected with the near-infrared camera (NIRCam) on board the James Webb Space Telescope (JWST). While NIRCam photometry is poorly sensitive to multiple populations among stars brighter than the main-sequence (MS) knee, the M-dwarfs more-massive than ∼0.1 define a wide color range due to multiple populations. The star-to-star color differences are mostly due to the different amounts of water vapor (hence oxygen) that affect the spectra of M-dwarfs. The chromosome map unveils an extended first population (1P) composed of M-dwarfs with different metallicities and three main groups of second-population (2P) stars that are depleted in oxygen with respect to the 1P. I present the discovery of an MS of very-low-mass stars and tentatively associated it with a sequence composed of O-rich stars alone.

I describe (i) our recent updates on first star formation, with particular emphasis on their binaries, (ii) formation of low-metallicity stars and the transition of their initial mass functions with metal enrichment, and finally (iii) formation of supermassive stars from slightly metal-enriched gas by the newly found super-competitive accretion channel.

To look at propagating winds from evolved stars into the interstellar medium is to look at how they are sustained. To understand their origins, we must look to the circumstances that create them in the first instance. In this article, I examine the physical conditions under which pulsation-enhanced, dust-driven winds are first generated. These initial conditions can help constrain the late evolutionary stages of these stars and provide insight into the mechanisms that cause the mass loss itself.

I review the methods, mostly developed in the last decade, that are commonly used to identify and characterize multiple populations (MPs) in Globular Clusters (GCs) based on photometry. I summarize the results from the recent surveys of MPs with the Hubble Space Telescope (HST) and ground-based facilities and provide a list of the main properties of MPs as inferred from these studies.

We recently discovered that NGC 3201 has characteristics that set it outside the current twofold classification scheme for Galactic globular clusters (GCs). Most GCs are mono-metallic and show light-element abundance variations (e.g., Na-O and C-N anti-correlations); but a minority of clusters also present variations in Fe correlating with s-process element and C+N+O abundances, and they possess multiple C-N sequences. These anomalous GCs also have a broad sub-giant branch (SGB) and follow the same mass-size relation as dwarf galaxies possibly evolving into GCs. We now revealed that NGC 3201 belongs to neither group. It has multiple C-N sequences, but no broad SGB, no strong evidence of a Fe-spread, and it does not follow the mass-size relation.

The internal dynamics of multiple stellar populations in Globular Clusters (GCs) provides unique constraints on the physical processes responsible for their formation. Specifically, the present-day kinematics of cluster stars, such as rotation and velocity dispersion, seems to be related to the initial configuration of the system. In recent work (Milone et al. 2018), we analyzed for the first time the kinematics of the different stellar populations in NGC 0104 (47 Tucanae) over a large field of view, exploiting the Gaia Data Release 2 proper motions combined with multi-band ground-based photometry. In this paper, based on the work by Cordoni et al. (2019), we extend this analysis to six GCs, namely NGC 0288, NGC 5904 (M 5), NGC 6121 (M 4), NGC 6752, NGC 6838 (M 71) and further explore NGC 0104. Among the analyzed clusters only NGC 0104 and NGC 5904 show significant rotation on the plane of the sky. Interestingly, multiple stellar populations in NGC 5904 exhibit different rotation curves.

I would like to review recent efforts of detailed chemical abundance measurements for field Milky Way halo stars. Thanks to the advent of wide-field spectroscopic surveys up to a several kpc from the Sun, large samples of field halo stars with detailed chemical measurements are continuously expanding. Combination of the chemical information and full six dimensional phase-space information is now recognized as a powerful tool to identify cosmological accretion events that have built a sizable fraction of the present-day stellar halo. Future observational prospects with wide-field spectroscopic surveys and theoretical prospects with supernova nucleosynthetic yields are also discussed.

We determined zirconium abundance in the atmospheres of 327 red giant branch (RGB) stars in the globular cluster 47 Tuc. The 1D LTE abundances were obtained from the archival VLT GIRAFFE spectra, using 1D hydrostaticATLAS9 stellar model atmospheres and synthetic Zr I line profiles computed with theSYNTHE package. The average zirconium abundance determined in the sample of RGB stars, 〈[Zr/Fe]〉 = +0.38 ± 0.12, agrees well with zirconium abundances obtained at this metallicity in the Galactic field stars, as well as with those observed in other Galactic globular clusters.

I present the latest results from our group about the multiple stellar populations in the old Milky Way globular clusters (GCs) and in the young systems both in the Magellanic Clouds and in the Milky Way. For the ancient GCs in our Galaxy I summarize the chemical properties of the stellar populations as observed on the chromosome map. Both Type I and Type II GCs are discussed. For the youngest clusters I will briefly report our latest spectroscopic analysis on the Large Magellanic Cloud cluster NGC 1818 and the Galactic open cluster M 11, which supports the co-existence of stellar populations with different rotation rates.

The standard scenario for the production of carbon-enhanced extremely metal-poor (CEMP) stars requires a more massive binary companion, which has evolved through the AGB stage and transferred carbon-rich material to the surface of the surviving, likewise extremely metal-poor (EMP) star. Evidently, the binary companion plays a key role in this process.

In order to characterise the polluting star, if any, the stage of evolution of the observed star (whether RGB or AGB), and whether pulsations exist, must be known. The Gaia DR2 parallaxes and photometry should contain the answer.

The factors controlling strong mass loss from evolved stars remain elusive, frustrating efforts to parameterise mass loss in models of evolved stars. We herein describe evidence we have collected to show that the mass-loss rate of stars is controlled by stellar pulsations, and that we are close to providing improved prescriptions for mass-loss rates from many kinds of evolved stars.

Much progress has been achieved in the age-dating of old stellar systems, and even of individual stars in the field, in the more than sixty years since the evolution of low-mass stars was first correctly described. In this paper, I provide an overview of some of the main methods that have been used in this context, and discuss some of the issues that still affect the determination of accurate ages for the oldest stars.

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 Non-Local Thermodynamic Equilibrium (Non-LTE) abundance corrections for Mg, Ca, and Fe in 12 ultra metal-poor (UMP) stars ([Fe/H] < −4.00). We show that they increase in absolute value toward the lower metallicity up to 0.45 dex for Mg, 0.30 dex for Ca, and 1.00 dex for Fe. This represents a first step toward a full Non-LTE analysis of chemical species in the UMP stars that will enable us to put useful constraints on the properties of the “First” stars.

We report the discovery by APOGEE of five mildly metal-poor ([Fe/H] >−1) anomalous giant stars in the halo/disk/bulge Galaxy with abundances of C, N, and Al that are typically found in globular cluster stars (GCs, see e.g. Carretta et al. 2009a; Mészáros et al. 2015; Pancino et al. 2017; Schiavon et al. 2017a; Tang et al. 2017) and in the inner Galaxy (e.g., Schiavon et al. 2017b; Recio-Blanco et al. 2017) simultaneously with atypical abundances of Mg (Mg-poor: [Mg/Fe] < 0) never before seen in Milky Way (MW) GCs, dwarf galaxies (see Hasselquist et al. 2017) neither in MW field stars. Additionally, four new moderately metal-poor ([Fe/H] <−1) anomalous giant stars (i.e., N-rich, Al-rich and C-poor) with trustly GCs second-generation like chemical patterns were identified within the Galactic bulge, halo and disk field.

It is widely accepted that binary interactions are responsible for the shaping of planetary nebula. However, these binary interactions and evolutionary channels are poorly understood. Our recent study revealed a newly discovered population of low-luminosity, low-metallicity, likely binaries in the Magellanic Clouds: dusty post-RGB stars. They are likely to have evolved off the RGB via binary interaction. In this paper we present preliminary results of the first radial velocity monitoring of the post-RGB stars in the Small Magellanic Cloud (SMC) and the implications on stellar (binary) evolution. We also investigate their link, if any, to the planetary nebulae systems.