Found 34 talks width keyword stellar populations

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.

Galaxy clusters are the perfect places to study both the always controversial nature vs nurture problem and the still not well understood evolution that galaxies follow. By studying the properties of the galaxies at different locations of the cluster we can assess the first problem, while studying the same properties over cosmic time, helps constraining the different proposed evolutionary theories. In this work we have focused in an intermediately-redshift rich cluster, RX J0152.7-1357 (z=0.83), by fully characterizing its stellar population properties with new state-of-the-art tools . By this means, we have derived for the first time in such a high-z cluster the ages, metallicities, abundance patterns and Star Formation Histories of the cluster ETGs on an individual galaxy-basis . The relations that these properties follow with galaxy velocity dispersion allow us to discuss a passive evolution scenario with respect to a cluster at z~0. Our results favor a downsizing picture where the relation between the position within the cluster, the velocity dispersion and the type of star formation history of the galaxies allow us to better understand the cluster evolution. We find that the most massive galaxies evolve passively while the lower-mass ones, generally located at the outskirts of the cluster, experience a more extended star formation history related to their later incorporation in the cluster.

Crucial issues in cosmology and astrophysics are to understand the
process of galaxy formation and evolution and the nature of what
appears to be the dominant form of matter in the Universe, i.e. dark
matter. Dwarf galaxies provide important information on both of these
issues. In this talk, I will focus on the dwarf galaxies found in the
Local Group, as it is the galaxy population that can be studied in
the greatest detail than any other from the properties of their
resolved stellar populations. I will show how wide-area surveys have
led to a leap forward in our observational understanding of these
galaxies and discuss future prospects.

The general picture of galaxy formation and evolution includes bars as the main drivers of the internal secular processes affecting the lifetime of disc galaxies. Bars are present in a very high fraction of all the spiral galaxies found at different redshifts, and the processes inducing their formation or the effects they may have on their host galaxies are still under discussion. Particularly interesting is the case of double-barred galaxies: at least 20% of all spirals have turned out to host not only one but two bars embedded in them. These two bars appear randomly oriented and independently rotating. The formation of such a double-barred system has been the goal of several numerical simulations and the results obtained so far can be roughly divided in two big groups: gas-rich and gas-free formation scenarios. In the same way a single bar does, double-bar systems might also promote gas inflow and contribute to the internal secular evolution. Moreover, they have also been proposed as a very efficient mechanism for the feeding of the active galactic nuclei.

All the previous theoretical hypothesis on the formation and evolution of double-barred galaxies have not been tested due to the lack of observational works focused on these systems. With this motivation, during my PhD I observed a sample of double-barred galaxies in order to fully analyse their kinematics and stellar populations. Among the most interesting results, it is important to highlight the discovery of the sigma-hollows, which are the only known kinematical signature of the presence of inner bars, or the fact that inner bars are younger and more metal-rich than their surrounding regions. In this talk I will present the whole work and discuss the results in the framework of the different formation scenarios and the role that these inner bars may be playing in the evolution of their host galaxies.

Taking advantage of the ultra-deep near-infrared imaging obtained with the Hubble Space Telescope on the Hubble Ultra Deep Field, we detect and explore for the first time the properties of the stellar haloes of two Milky Way-like galaxies at z~1. We find that the structural properties of those haloes (size and shape) are similar to the ones found in the local universe. However, these high-z stellar haloes are approximately three magnitudes brighter and exhibit bluer colours ((g-r)<0.3 mag) than their local counterparts. The stellar populations of z~1 stellar haloes are compatible with having ages <1 Gyr. This implies that the stars in those haloes were formed basically at 1<z<2. This result matches very well the theoretical predictions that locate most of the formation of the stellar haloes at those early epochs. A pure passive evolutionary scenario, where the stellar populations of our high-z haloes simply fade to match the stellar halo properties found in the local universe, is consistent with our data.

In recent years accurate photometric and spectroscopic observations have
provided sound evidence that Galactic Globular Clusters can not be longer
considered the prototype of Simple Stellar Populations. In this talk we
present the most recent updates concerning the empirical evidence and
discuss the theoretical framework required for interpreting observations.
Current shortcomings in the interpretation of how the multiple stellar
populations formed in a given cluster are also discussed.

The classical idea that globular clusters are the prototypes of simple stellar populations has been revolutionized in the last few years. Multiple sequences of stars have been detected in the colour-magnitude diagram of a number of clusters, mostly thanks to high-precision HST photometry, and the correlation with the chemical properties of different generations of stars has been demonstrated. In this talk, we will first present a summary of the observational picture, and we will then introduce the SUMO project (a SUrvey of Multiple pOpulations). This is a long-term project, lead here at the IAC and aimed at detecting and characterizing multiple populations in a large sample of globular clusters. We will review the scope, the observing and reduction strategy, and the first results. So far, data for more than 30 clusters have been secured, using the wide field imagers available at the 2.2m ESO/MPI and INT telescope, thus covering both hemispheres. We will present a new photometric index which turned out to be very effective in detecting multiple RGBs in nearly all the clusters analyzed so far. The connection with the chemical content of the different populations will be also discussed.