We present a brief, comparative, study of the morphology of a sample of 9 late type, star forming, local galaxies, as seen in different bands. The objects are present in the “The Hα Galaxy Survey” by James et al., 2004 (J04 hereafter), in the Sloan Digital Sky Survey (“SDSSS”, York et al., 2000), and also in data from GALEX (Martin et al. 2005). We tested the pixel to pixel proportionality v. Hα of images in broad bands from FUV to NIR. We also analyzed the differences in the radial profiles of light in different bands. Finally, we also measured several parameters of the morphology of the distributions of light, as detected in bands of SDSS (u,g,r,i,z), GALEX (NUV, FUV) and in R and Hα from J04, aiming to test which bands better mimic the spatial distribution of the SF as traced by Hα. Our goal is to acquire as accurate a determination as possible of the spatial distribution of the massive star formation in local galaxies, to compare with the analogous distribution in galaxies at increasing redshift.

We present a preliminary analysis of the stellar populations in the central parsecs of a sample of 22 Seyfert 2 galaxies, based on a careful separation of nebular emission and stellar light in high-spatial resolution HST-STIS spectra. 10% of the surveyed nuclei display stellar populations of intermediate age, ∼1-2 Gyr old, whereas the remaining targets appear to be evenly split between objects showing only very old stellar populations and nuclei requiring also an additional blue featureless component, which we characterise by means of very young, few-Myr-old stars. The small fraction of stellar population of intermediate age seems to argue against the presence of such a young component, however, since the short lifetime of O-stars would imply recurrent star-formation episodes and the build-up over the last 1-2 Gyr of a detectable intermediate-age population. Additionally, a correlation between the luminosity of such a blue component and the emission from highly-ionised species, together with the general absence of Wolf-Rayet features, further suggests that the featureless continuum arises from the central engine rather than from star-forming regions. We discuss our results in the framework of the unification paradigm and of models for star formation close to supermassive black holes.

The globular cluster ω Cen is an outstanding object in terms of both its chemical and kinematic properties. Its large mass, spread in element abundances, chemical and kinematical segregations, as well as its peculiar orbit, all suggest that it is the surviving remnant of a larger system. In this contribution we deal with the chemical evolution of ω Cen in the framework of a model where it is the remnant of a dwarf spheroidal galaxy evolved in isolation and then swallowed and partially disrupted by the Milky Way. Both infall of primordial matter and metal-enriched gas outflows are necessary in order to reproduce the observed stellar metallicity distribution function, age-metallicity relation and several abundance ratios. Yet, as long as an ordinary stellar initial mass function and standard stellar yields are adopted, we fail by far to get the enormous helium enhancement required to explain the double main sequence of ω Cen.

Here, we present our on-going work on the determination of stellar parameters of giants in the Galactic Disks and Bulge observed with UVES on the VLT. We present some preliminarily results.

The stellar populations of a galaxy are a fossil record of its formation and evolution and the various physical processes involved. Therefore, studying the resolved stellar populations of nearby galaxies can provide important constraints on their structure, formation, and evolution. To that end, we have obtained VI photometry with the Advanced Camera for Surveys on the Hubble Space Telescope for three fields at deprojected radii Rdp ∼ 9 − 13 kpc (∼ 4 − 6 visual scale lengths) along M33's southeast minor axis. We present results for the star formation history (SFH) of these fields based on the technique of synthetic CMD fitting.

We present a study of the morphologies and stellar content of the galaxies in the central ∼ 74”×64” region of the galaxy cluster Abell 2218 (see Fig. 1). The spectroscopic data were obtained with the integral field unit PMAS (Roth et al. 2005) in the PPAK mode (Verheijen et al. 2004; Kelz et al. 2006), at the 3.5 m telescope of the Calar Alto Observatory. The covered wavelength range was 4650–8000 Å, with a spectral resolution FWHM∼ 10Å. These data were combined with with deep HST/ACS F475W, F555W, F625W and F850LP imaging, and additional data from the literature.

In Fig. 2 we show the rest-frame B-V vs. MV colour-magnitude diagram for the identified cluster members. The data are segregated according to an objective morphological classification based on the Sérsic index. Contrary to previous results (e.g. Ziegler et al. 2001; Smail et al. 2001) there is a clear indication that the cluster population is not dominated by early-type galaxies, and that there exists an almost parity between early- and late-type objects. In addition, the late-type galaxies spread over a wider range of colours and luminosities with respect to the early-types. This indicates that early-type objects are more massive and have older stellar populations, while late-type galaxies are less massive and exhibit a wider range of stellar population properties.

The results agree with the two-steps scenario for the evolution of galaxies in clusters (e.g. Poggianti 2003), which explains the co-existence of a primordial population of early-type galaxies formed at early epochs, with an additional population of late-type galaxies that have been captured by the cluster, infalling, suffering a short enhancement of the star formation that is later quenched by the interaction with the environment, and that afterwards evolved passively, becoming redder and fainter. Finally, galaxy-galaxy interactions and dry merging processes were responsible for the building up of new massive spheroidal galaxies.

Full details are given in Sánchez et al. (2007).

We combine together physical parameters estimates for a large sample of galaxies drawn from the Sloan Digital Sky Survey Data Release Two (SDSS DR2), spanning wide ranges in galaxy properties, in order to provide a census of the physical parameters of galaxies in the local Universe. Stellar metallicities, masses and ages for this sample have been estimated comparing the strengths of selected absorption features in each observed spectrum to a comprehensive Monte Carlo library of star formation histories, following a Bayesian statistical approach. This allows us also to derive the total amount of metals locked up in stars today, and hence the average stellar metallicity of galaxies in the local Universe, finding a value of . We also quantify the relative contribution to the total densities of mass and metals in stars from galaxies with different properties.

One of the main ingredients of current stellar population models is a library of stellar spectra. Both empirical and theoretical libraries are used for this purpose, and the question about which one to use is still being debated in the literature. Empirical and theoretical libraries are improving significantly over the years, and many libraries have become available lately. It is not clear what are the advantages of using each of these new libraries, and how far behind are models compared to observations. Here we compare in detail some of the modern theoretical libraries availabe in the literature against empirical libraries attempting to detect their weaknesses and strengths. The aim is to be able to compute in the short future a new synthetic stellar library that combines the best qualities of the current available ones, while improving considerably their weaknesses.

Heliocentric (UVW) and galactocentric (VR VΦ VZ) space motions were derived for 38 RR Lyrae (RRL) and 79 blue horizontal branch (BHB) stars in a 200-sq degree area near the North Galactic Pole (NGP). A kinematic analysis of the 26 RRL and 52 BHB stars whose height (Z) above the plane is < 8 kpc shows that the sample is not homogeneous. Our BHB sample shows zero galactic rotation and roughly isotropic velocity dispersions. whereas the RRL sample shows a definite retrograde rotation and non-isotropic velocity dispersions. The combined BHB and RRL sample shows a smaller retrograde rotation that is similar to that found by Majewski et al. (1996) for a sample of subdwarfs in SA 57 at the NGP. There are significantly more RRL with negative W-velocity (streaming down) than positive W-velocity, whereas the numbers of BHB stars are comparable. This indicates the presence near the NGP of an accreted halo component that is rich in RRL (probably Oosterhoff type I) stars.

These results are presented in detail in a forthcoming paper (Kinman et al. 2007).

Metal-rich globular clusters are important to study the chemical evolution of the Galaxy and one of the best approaches to better understand the physical processes occurring in stellar populations as building blocks of galaxies. We report on Mn, Cu, and Zn abundances of giant stars in metal-rich Galactic globular clusters (−0.70 < [Fe/H] < −0.11), measured on spectra obtained with the UVES spectrograph on the 8-m VLT UT2-Kueyen telescope.

The nearby Virgo Cluster provides an ideal laboratory to study galaxy-galaxy and galaxy-cluster interactions at a level of detail impossible at higher redshift. In Virgo, there exists a large population of spiral galaxies with mostly undisturbed stellar disks, but truncated gas disks. We present results of an observational study of several of these galaxies, utilizing optical and UV imaging, and optical spectroscopy. By combining optical spectroscopy and UV imaging, we are able to constrain the time since star formation endedin the outer disk and, therefore, constrain the time since the galaxies were stripped. Our results show that while most of the galaxies in our sample are consistent with being stripped near the cluster center, several show evidence for being stripped well outside the core, suggesting that the “reach” of the intracluster medium is greater than is suggested by simple ICM models.

We have computed new models for stars of low and intermediate mass, with varying degrees of α-element enhancement factors, using new low-temperature molecular opacities. We present some of the effects found.

I discuss how galaxy fundamental parameters that are derived by comparing observational data with stellar population models, depend on the adopted models. The emphasis is on the treatment of the Thermally-Pulsing Asymptotic Giant Branch (TP-AGB) stellar phase, that is a source of major discrepancy between the various model renditions. In particular, I show that ages and stellar masses of galaxies decrease when models including an empirically-calibrated TP-AGB phase are considered. Illustrative examples are provided for a wide redshift range. Constraints to galaxy formation models need revision on the light of these results.

The impact on the predicted Teff scale of using the latest MARCS model atmospheres, instead of a fixed atmospheric structure (e.g., the gray T–τ relation) is examined. The former were fitted to stellar interior models at both the photosphere and at τ = 100 to determine the sensitivity of evolutionary tracks and isochrones for [Fe/H] = 0.0 and −2.0 to the chosen fitting point. In the case of solar abundances, the Teff of the giant branch varied by up to 100–150 K, depending on how the outer layers were treated. Much smaller variations were found for metal-poor giants (or main-sequence stars). Interestingly, models for the low solar Z favored by Asplund et al. (Z=0.0125) were unable to reproduce the gap near the turnoff in the C-M diagram of the old open cluster M 67, in contrast to models that assume Z=0.0188.

We are using full spectrum fitting to determine the ages and metallicities of Galactic clusters (M67 and globular clusters). We find that the method is very accurate to measure the metallicity. Blue horizontal branches are well identified as a ‘young’ sub-component, and the age of the ‘old’ component is in fair agreement with CMD determinations.

The stellar binary fraction in star clusters is a key factor in understanding the effects of binary stars on the properties and dynamical evolution of the host cluster. Using a very accurate stellar catalogue based on deep Hubble Space Telescope (HST) observations of the young rich Large Magellanic Cloud cluster NGC 1818, we assess its binary content. Based on artificial star tests we have established a method to very efficiently determine the probability of chance blends and superpositions. Combining the measured photometric errors and the superposition statistics, we construct synthetic colour-magnitude diagrams (CMDs) as a function of input binary fraction. The binary fraction of the cluster is then calculated by means of a Kolmogorov-Smirnoff (K–S) test between the synthetic and the observed CMDs. The likely binary fraction for this cluster is 50–70.

We present results from a series of projects aimed at better understanding the ages, velocities, metallicities, and distances of populous clusters in the LMC. Using FORS2 on the VLT, we obtained near-infrared spectra for more than 200 stars in 28 LMC clusters, which span a large range of ages and metallicities. The strong absorption lines of the Ca II triplet are used to calculate cluster velocities and abundances. We determine cluster ages through main sequence fitting of theoretical isochrones to deep optical photometry using a combination of published photometry, VLT FORS2 images and archival HST WFPC2 images. As shown by Grocholski & Sarajedini, a cluster's age and [Fe/H] can be used to predict the K-band luminosity of core helium burning red clump (RC) stars in that cluster. Using ISPI on the CTIO 4m telescope, we imaged 17 LMC clusters in the J– and K–bands, with the resulting photometry reaching ∼0.5 mag below the RC. We combine the measured apparent RC magnitudes with the predicted absolute values to determine absolute distances to each of these clusters and thereby probe the structure of the LMC as traced by its intermediate-age clusters.

We present integral-field observations of kinematically decoupled components (KDCs) in a sample of 24 Sa galaxies part of the SAURON Survey. We show how the V/σ maps can be used to highlight the presence of the KDC and investigate their stellar populations (i.e. age) to understand their origin (i.e. secular vs hierarchical scenarios). We find that KDCs can be long-lived and are typically well aligned with the galaxies kinematical major axis, supporting mounting evidence that secular evolution becomes important at intermediate redshifts. Dynamically colder ones seem to host younger stellar populations. We also relate these features to the ones found in our sample of 48 elliptical and lenticular galaxies. We find that there is no age vs size relation for these decoupled components in Sa galaxies, suggesting that the dominant factor determining their size is the amount of star formation they have been subject to during their life time.

Evolutionary synthesis models (ESM) have been extensively used to obtain the star formation history in galaxies by means of SED fitting. Implicit in this use of ESM is that (a) for given evolutionary parameters, the shape of the SED is fixed whatever the size of the observed cluster (b) all regions of the observed SED have the same weight in the fit. However, Nature does not follow these two assumptions, as is implied by the existence of Surface Brightness Fluctuations in galaxies and as can be shown by simple logical arguments.

The possibilities and problems of using calculated spectra from model atmospheres when analysing stellar populations in galaxies are reviewed. Various types of consistency tests for stellar models are discussed, as well as comparisons with observational data. It is argued that major improvements in the model spectra are possible and worthwhile.