Found 30 talks width keyword stellar populations
APOGEE contains more than hundred thousands new giant stars. This enabled
us to collected an unprecedented and homogeneous sample of giant stars with
light-element abundance variations similar to observed in “
*second-generation*” globular cluster stars. If they are really former
members of dissolved globular clusters, stars in these groups should show
some of the basic SG-like chemical patterns known for stars currently
belonging to the Milky Way globular clusters, such as depletion in C and O
together with N and Al enrichments. Here, I will present the results of an
updated census of *SG-like* stars from a near-infrared manual analysis
using the Brussels Automatic Stellar Parameter (BACCHUS) code to provide
the abundances of C, N, O, Mg, Si, Al, Fe, Ce and Nd for every line of
possible cluster member stars, which they migrate to the disk, halo and
bulge as unbound stars, and become part of the general stellar population
of the Milky Way. By combining wide-field time-series photometry with
APOGEE-2S spectroscopy data, we are in a good position to put the big
picture together. The VVV survey have produced a large variability dataset
towards the Milky Way bulge and disk, including data in the near-IR (J and
Ks). These data will allow us to place constraints on the “polluters" that
are responsible for the chemical peculiarities, with candidates including
TP-AGB stars, binary mass transfer, accretion of material from the winds of
AGB stars, etc. A cross match between VVV sources and APOGEE targets is
The most metal-poor stars in the Galaxy are relics from the first generations of star formation, and their properties can reveal key information about the formation and evolution of the Milky Way. However, only a small number of these extremely rare stars are currently known, due to the difficulty in finding them amongst the overwhelmingly more abundant stars of higher metallicity. In this talk, I will present the Pristine survey, a narrow-band photometric survey in the wavelength region around the Ca H&K absorption lines designed to efficiently search for extremely metal-poor (EMP) stars. In the first three years of the survey, we have covered ~2,500 square degrees of sky in the Northern hemisphere using the CFHT on Mauna Kea in Hawaii, as well as a sizeable spectroscopic follow-up sample using mostly the INT and WHT in La Palma. With this data, we have demonstrated success rates of 70% for finding stars with [Fe/H] < -2.5, and 22% for stars with [Fe/H] < -3.0. This represents a significant improvement upon previous searches for EMP stars, which have reported success rates of 3-4%. With this efficiency, the Pristine survey is poised to make a significant contribution to constraining the metal-poor tail of the metallicity distribution function, as well as increasing the number of known ultra metal-poor (UMP) stars in the literature. In addition, I will discuss how the Pristine survey is being used to characterise the faint dwarf galaxy population, and analyse substructure in the Galactic Halo.
Galactic Archeology is today a vibrant field of research. The adoption and launch of the Gaia astrometric satellite by ESA has resulted in many spectroscopic Galactic surveys that aim to complement the Gaia data with information (for the fainter Gaia stars) about stellar elemental abundances, radial velocities, and stellar parameters. This results in multi-dimensional data sets which will allow us to put the Milky Way stellar populations into a much broader galactic context, eg by comparing with models and galaxies at large look-back times. In this talk I will review a selection of recent exciting developments in Galactic Archeaology found via on-going surveys as well as look to the future and see what surveys like 4MOST and WEAVE will bring. The proposed surveys will be put into a wider context of past, on-going and future spectroscopic surveys and how this can all be combined to understand the Milky Way as a galaxy.
Recent works show that the restframe colours of X-ray selected AGN host galaxies at z~1 are no different from those of inactive galaxies once stellar mass selection effects are taken into account. However, there is a clear deficit of AGN among quiescent galaxies, and the average star formation rates of AGN hosts are comparable or higher than those of inactive star-forming galaxies. These apparently contradictory findings could be a consequence of higher extinction in star-forming AGN hosts compensating for their younger stellar populations in observed colours. In this talk I will present a new method of extinction correction that breaks the degeneracy with stellar age and metallicity by comparing the restframe U-V colour with measurements of the Dn(4000) index on intermediate band photospectra from SHARDS. I'll show that the distribution of extinction corrected U-V colours and Dn(4000) for AGN hosts at z<1 is significantly different from that of comparison samples of inactive galaxies, with a clear deficit of AGN in intrinsic red galaxies and a higher prevalence among those with intermediate age stellar populations.
Stellar population synthesis has reached a high degree of sophistication that has been exploited to understand to a certain extent the mechanisms of formation, assembling, and evolution of galaxies in our universe. Progress is based on solid results in the field of stellar evolution and spectrophotometric observations of large numbers of stars and galaxies. However, there are certain phases of stellar evolution, like the thermally pulsing asymptotic giant branch (TP-AGB) phase, the Wolf-Rayet stage, and the presence of interacting binaries, whose treatment is either ignored or extremely simplified in galaxy evolution models due to the uncertainties in their description. In this talk I will present results from models that add the state of the art in the treatment of these evolutionary phases to traditional population synthesis models.
Since the early 50' of last century the study of Horizontal Branch stars in Galactic GCs has been of pivotal relevance since the core He-burning stage is an 'amplifier' of any evolutionary/physical process occurring during the early evolutionary stages. Thanks to the huge observational effort devoted to this issue many outstanding 'anomalies' have been discovered concerning the physical properties of GC HB stars. The situation is becoming more complex when accounting for the discovery of the Multiple Population phenomenon in Galactic GCs. We will review the main anomalies related to the HB evolutionary stage, their (when available) theoretical interpretations, and current shortcomings. We will also discuss how the discovery of the Multiple Population Phenomenon offers a new approach for interpreting many observational evidence.
Many stars are observed to belong to multiple systems. Interactions between binary stars may change the evolutionary track of a star, creating atypical stars like Blue Stragglers and explaining the existence of extreme horizontal branch (EHB) stars. Using evolutionary population synthesis models including binary star evolutionary tracks from Hurley et al. and including the two He white dwarfs merger channel, suggested by Han et al., for the formation of EHB stars we compute a series of isochrones which include these atypical stars. We derive the integrated spectral energy distributions and the colors corresponding to these populations. The predictions of this model are in good agreement with traditional population synthesis models, except when the spectrum of the stellar population is dominated by binary stars or their products, e.g., EHB stars in the ultraviolet (UV) of early-type galaxies (ETGs) (Hernández-Pérez and Bruzual 2013). Using this binary population synthesis model we reproduce successfully the observed colour-colour diagram of a sample of 3417 ETGs observed both in the optical (SDSS -DR8) and the UV (GALEX-GR6) (Hernández-Pérez and Bruzual 2014). I will show how important is to consider binary interactions in evolutionary synthesis models.
I will talk about how resolved stellar populations in the nearby Local Group dwarf galaxies have been used to study the detailed chemical, kinematic and star formation history of these systems and the link to the properties of the Milky Way. I will mainly discuss the results from the DART spectroscopic surveys of nearby dwarf spheroidal galaxies, determining detailed abundances, looking for CEMP stars and also combining spectroscopy with colour-magnitude diagram analysis to measure the time scale for star formation and chemical evolution.
The Magellanic Clouds are the closest star forming galaxies, and their star formation histories can be derived in great details from color-magnitude diagrams reaching the oldest main sequence turnoffs. In the last several years, we have been conducting a wide research program on the Magellanic Clouds, including both photometry and spectroscopy, and have analysed the star formation history across both the Large and the Small Magellanic Clouds. This has revealed the nature of the stellar population gradients of these galaxies, as well as signatures that can possibly be related to their interaction history, among them and with the Milky Way.
Dwarf galaxies are a complex population. They comprise objects with young and old stellar populations, slow and fast rotation, as well as single- and multi-component structure. These characteristics show correlations with environmental density - we thus believe that dwarf galaxies hold a fossil record of how environment affected galaxy evolution. In this talk I will review and discuss recent progress on our understanding of dwarf galaxies in clusters, both from the observational and the modelling side. In particular, I will attempt to reconcile the proposed formation mechanisms of early-type dwarf galaxies - the most abundant population in clusters - with the continuous environmental influence predicted by cosmological simulations.
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