Despite the tremendous amount of spectroscopic data available for Galactic globular cluster stars, several fundamental questions regarding their complex formation and evolution remain yet unanswered. In the general framework of multiple population (generation?) scenarios, an extensive comprehension of the stellar source of pollutions (and its relationship with global cluster parameters) is...
The presence of more than one stellar population in globular clusters (GCs) is one of the most intriguing topics in the field of stellar populations. Recently, we have understood that the properties of the different populations are best constrained by precise chemical abundances coupled with the nicknamed "Chromosome Maps" photometric diagram. Reading the "Chromosome Maps" by using the...
To decipher the history of the Galactic bulge is a tricky task because of the complex stellar populations that live there from other components of the Milky Way. In particular, the globular clusters are fundamental pieces to reconstruct that history since they retain the chemodynamical signatures of the early stages of the Galaxy. In this context, we have the globular cluster Palomar 6 (Pal6),...
Black holes in star clusters
Stellar-mass black hole candidates have been reported in several Milky Way globular clusters, based on either accretion signals or radial velocity variations of companion stars. These individual black holes probably represent much more abundant populations of black holes. Charting the demographics of black holes in clusters helps to understand the contribution...
Globular clusters are excellent laboratories to study star formation and the early evolution of galaxies since they contain large samples of equidistant stars with similar ages and chemical abundance patterns. In addition, their high stellar densities make them unique environments for the creation of exotic stars like low-mass X-ray binaries, millisecond pulsars and merging black hole...
In the last 15 years, several spectroscopic investigations seem to indicate an anomalous chemical composition of young Galactic open clusters and star-forming regions, which include (but is not limited to) sub-solar iron (Fe) abundances of these systems in the solar neighborhood, extreme and unexpected barium (Ba) enhancements (with apparently solar values of lanthanum, La), and super-solar...
Open star clusters are unique tracers of the Galaxy evolution and excellent laboratories to study stellar physics. The huge volumes of data produced by current (and future) low- and medium-resolution surveys are expected to push these fields forward. However, at the end of this decade there are going to be gaps in knowledge that can be filled through complementary high resolution data. Here I...
Star clusters and dwarf galaxies are powerful astrophysical laboratories to address several open issues in modern astronomy, ranging from stellar evolution to cosmology. Stellar kinematics is a unique tool in this context. In particular, precise and accurate stellar velocities allow us to measure the mass of a stellar system (including its dark components and their spatial distribution), to...
Recently, we have studied barium lines in high-quality spectra of two metal-poor giants in the
Galactic halo. The hyperfine splitting effects on the barium lines seem to confirm the theoretical expectation that both r-process events and also s-process contribution by rotating massive stars have polluted the ancient halo of our Galaxy.
Nowadays, this kind of result can be achieved only for...
The abundances of CNO isotopes provide powerful diagnostics of different physical processes acting in stars and galaxies. In particular, carefully chosen isotopic ratios allow us to set useful constraints to galactic chemical evolution (GCE) models, with special regard to the shape of the integrated galaxy-wide stellar initial mass function. After a brief recap of the significance of the CNO...
In the last few years, the synergy between spectroscopy and asteroseismology was key to the improving the precision and accuracy of the inferred stellar properties (surface gravity, effective temperature, chemical composition, radius, mass, age).
For instance, given the difficulties associated with measuring log g via spectroscopic analyses, large-scale spectroscopic surveys have now...
New spectrographs like HRMOS hold great promise to provide high-precision abundance measurements through high-resolution spectra of dozens of stars at a time. However, the chemical composition of stars cannot be directly measured from their spectra, but must be estimated through comparisons to theoretical radiative transfer calculations. At present, shortcomings in this theory are holding back...
High resolution spectroscopy has fundamentally shaped my scientific career and has consequently become my stock in trade. I will present several benchmark examples of my work with high resolution spectroscopy of stellar spectra (a definitely biased point of view but which became relatively extensive overtime), illustrating the needs and requirements for future high resolution spectrographs...
In their youth, low-mass (0.1-1.5 Msun) stars are rapidly rotating, magnetically active and may be accreting gas from a circumstellar disk. As they age, planets form and possibly migrate, disks disperse and stars spin down, becoming less magnetically active. The magnetic field, generated by a rotation-driven dynamo process, plays a key role in all of these events; the stressing and twisting...
Young stellar objects are characterised by highly dynamical processes related to the interaction of the still accreting star and its proto-planetary disk. These include accretion of matter, funnelled through magnetic field lines from the disk to the stellar surface, as well as mass ejection in the form of collimated jets and disk winds, responsible for the disk dissipation and removal of...
One method to estimate stellar ages is based on the so-called chromospheric activity (CA), according to which we can infer that chromospherically active isolated objects must be young. At the same time, stellar orbits in the Galaxy give rise to a statistical relationship according to which anomalous velocities are probably associated with old stars. This work was built in function of objects...
HRMOS will enable radial velocity searches for planets in clusters and towards the Galactic bulge at a scale previously unobtainable with single-object spectrographs. At present, the most comparable cluster planet searches have been for transiting planets with wide-field cameras. We have led a transiting planet search using data from the Kepler telescope towards NGC 6791, an old, metal-rich...
I will present a new probe of possible variations in the fine-structure constant on Galactic size-scales: solar twins and analogues. This method has been demonstrated on local solar twin spectra from ESO HARPS. We have also recently discovered much more distant solar twins, 4kpc closer to our Galaxy's centre, where the dark matter density is 3 times higher than the local environment. ESPRESSO...
The Gaia-ESO Survey is a very ambitious project to obtain high-quality spectra of 100,000 stars, representing the major stellar populations, from young open star clusters to the oldest field stars, O-stars to M-stars. Gaia-ESO used the VLT GIRAFFE facility, allowing both good signal-noise spectra and also sampling beyond the immediate Solar neighbourhood for unevolved stars. Key features...
The GALAH survey is a large Australian-led project with a goal to measure radial velocities and ~30 elemental abundances in 1 million stars. Using the HERMES spectrograph at the AAT, GALAH has now observed 750,000 unique stars across three affiliated surveys including the main archaeology program, and associated science arising from the K2GAP and TESS surveys. The advent of Gaia has proved a...
Gaia benchmark stars are selected to be calibration stars for different spectroscopic surveys. Very high-quality and homogeneous spectroscopic data for these stars are therefore required. We used ultrahigh- and high-resolution spectra obtained with the ESPRESSO, PEPSI, and HARPS spectrographs to measure spectral line characteristics and determined stellar parameters and abundances for these...
4MOST is a spectroscopic survey facility that will be placed on the Vista telescope on Paranal in Chile. It will be able to simultaneously obtain spectra for about 2400 objects, 800 at a resolution of about R~20000, and 1600 at a resolution of about R~5000. I will give a brief overview of the 4MOST science cases and give a few possible examples where follow-up observations with a...
In this talk, I will present a comprehensive catalog (Survey of Surveys, SoS) to meaningfully merge the main parameters of the largest ground-based spectroscopic surveys to date (RAVE, APOGEE, GALAH, Gaia-ESO, and LAMOST) using Gaia astrometry as reference. The main steps for the compilation of SoS include i) the cross-match algorithm (XM) between Gaia and the spectroscopic surveys, ii) the...
The holy grail of Galactic Archaeology is the constrain the physical processes responsible for of the formation, evolution and assembly of Milky Way-like galaxies. With current technology, the best way to do this is to use the Milky Way as a laboratory to answer questions of galaxy formation using the detailed spatial, kinematic, and chemical information for its billions of stars. In this...
Our ability to detect planets around stars with the radial-velocity (RV) method has a strong dependence on our understanding on the stellar jitter of such stars which can reach dozens of m/s in red giants. This intrinsic RV variability can be caused by stellar magnetic activity, pulsations or granulation and it behaves on a different way depending on the spectral type of the stars and on their...
The chemical evolution of galaxies is governed by the chemical yields from stars, especially from Asymptotic Giant Branch (AGB) stars. Observations from Post-Asymptotic Giant Branch (post-AGB) stars serve as exquisite tools to quantify and understand AGB nucleosynthesis. Our studies have shown that AGB nucleosynthesis is riddled with complexities. In this talk, I will present the invaluable...
Measurements of elemental abundances and their isotope ratios allow us to perform key tests of mixing mechanisms inside stars and provide powerful diagnostics of chemical enrichment in galaxies across cosmic time. For this purpose we need large samples of stars with precise chemical abundances over a full range of metallicities and other stellar atmospheric parameters, a full range of masses,...
Dwarf galaxies and larger satellite galaxies are ideal laboratories to study the earliest chemical evolution, different nucleosynthetic channels, dark matter structure, and hierarchical galaxy formation. The Milky Way has dozens of satellites which can be studied in far greater detail than their more distant counterparts. With upcoming large spectroscopic surveys such as 4MOST and WEAVE, these...
We investigate the contribution of sub-Chandrasekhar mass Type Ia supernovae to the chemical enrichment of the Gaia Sausage galaxy, the progenitor of a significant merger event in the early life of the Milky Way. Using a combination of data from Nissen & Schuster (2010), the 3rd GALAH data release (with 1D NLTE abundance corrections) and APOGEE data release 16, we fit analytic chemical...
I will discuss the potential for HRMOS in studying the stars that are escaping from globular clusters into the halo field through streams or extratidal structures. These stars allow us to address questions of globular cluster origins, abundance anomalies, and chemical tagging, as well as dynamics, mass loss, and dark matter. The large-scale spectroscopic surveys planned for the 2020s will...
The halo of our Milky Way is scarred by galaxy formation in the form of stellar streams. These streams are a uniquely powerful tool for understanding the building blocks of the Milky Way’s stellar halo, the mass and shape of the Milky Way’s halo, and ultimately the nature of dark matter. Each stream is the remnant of a dwarf galaxy or globular cluster; the former are especially interesting as...
The homogeneous comparison between the chemical composition of the Milky Way (MW) and its more massive satellites (Large Magellanic Cloud - LMC and Sagittarius - Sgr) reveals that the latter galaxies have different chemical abundances with respect to the MW stars for almost all the species. In particular the largest difference is measured for [V/Fe] and [Zn/Fe], reaching up to 0.5/0.7 dex for...
The properties of the first stars remain unknown. The chemistry of relic environments, enriched only by the supernovae of the first (Pop III) stars, may offer the best opportunity to uncover their properties (e.g. mass distribution and explosion energies). In this talk, I will present the analysis of two of the most chemically near-pristine gas reservoirs at a redshift z~3 observed using a...
Modern-day machine learning generative models allow us to directly model the distribution of the observed spectroscopic data, even when the stellar labels are absent. In recent years, we have seen the explosion of studies in terms of supervised machine learning. However, the exploration of unsupervised generative models in stellar spectroscopy is, unfortunately, lagging behind. In this talk, I...
High-resolution spectroscopic surveys of the Milky Way have entered the Big Data regime, and have opened avenues for solving outstanding questions in Galactic Archaeology. However, exploiting their full potential is limited by complex systematics, whose characterization has not received much attention in modern spectroscopic analyses. We present a novel method to disentangle the component of...
In this talk I will give a general overview of the HRMOS spectrograph concept design for the VLT . Different approaches and optical solutions will be also discussed in order to be compliant with the scientific requirements.
The proposed HRMOS is the next step in pursuing, on a large scale, precise chemical characterisation of stellar populations. A number of new medium-to-low resolution spectroscopic survey instruments, in operation or under development, provide a wealth of data on a very large scale from which key subsets can extracted as input to higher resolution spectroscopic surveys (e.g. with HRMOS). While...
