We briefly review some constraints for stellar models in various mass regimes and evolutionary stages as provided by observational data from spectroscopy to multi-wavelenghts photometry. The accuracy of present generation of stellar models can be significantly improved only through an extensive comparison between theory and observations.

After a brief review of the observational evidences indicating how the populations of Be stars, red/blue supergiants, Wolf-Rayet stars vary as a function of metallicity, we discuss the implications of these observed trend for our understanding of the massive star evolution. We show how the inclusion of the effects of rotation in stellar models improves significantly the correspondence between theory and observation.

We characterize the stellar populations in the nuclear region of the barred spiral galaxy NGC 4900 using the integral field spectrometer OASIS and the synthesis code LavalSB and the code from Mollá & García-Vargas (2000) for the young (<10 Myr) and the old stellar populations, respectively. The high spatial resolution of the instrument allows us to find an old population uniformely distributed and younger regions located at the end of the galaxy bar and on each side of a nuclear bar.

The VLT Survey Telescope (VST) is going to offer a unique chance to collect deep and wide field photometry in multi-directions, opening the door to a definitive mapping of the Galactic halo. In this shortcoming scenario, we present a pilot study aimed at recovering the halo stellar density using the Capodimonte Deep Field (OACDF, Alcalá et al. 2004). Turn-off stars are isolated and the relative color-magnitude diagram (CMD) is compared with synthetic CMDs. Our result is consistent with a power law exponent n≈ 3 over a range of Galactocentric distances from 8 to 40 kpc.

We analyzed a sample of about 2500 stars extracted from the Sloan Digital Sky Survey with Teffin the range 4750÷6500 K and log g greater than 1.5. Atmospheric parameter estimates are obtained by comparing observed and synthetic spectral indices. The dependence of the α-enhancement phenomenon on stellar metallicity and on Galactic position is investigated.

We give a progress report on our work to reduce and calibrate spectra obtained for Hubble's Next Generation Spectral Library (NGSL). We will shortly be working with Bruzual and Charlot to incorporate these spectra into their stellar population synthesis code.

V, I time-series photometry of the new Milky Way satellite recently discovered in the Bootes constellation (Belokurov et al. 2006) was collected at the TNG, WIRO and Loiano telescopes and used to search for variable stars. We have identified a non-negligible population of RR Lyrae variables, which confirms the presence of an old population in this newly discovered structure. The distribution of periods coupled with information on the evolutionary status of the system derived fromthe color-magnitude diagram provide important hints on the nature and history of this intriguing new companion of the Milky Way.

The combination of stellar population synthesis models and photoionization models allows a better understanding of the spectral features of HII regions and HII galaxies. In this work we show that sampling effects in the initial mass function (IMF) are very important in the low cluster mass case. To this aim, we compute photoionization models ionized by realistic clusters made up of various combinations of individual stars and clusters made up with a synthesis model. We discuss the differences in the position on diagnostic diagrams and their implications.

We discuss SAURON absorption line strength maps of a sample of 24 early-type spirals, mostly Sa. From the Lick indices Hβ, Mgb and Fe 5015 we derive SSP-ages and metallicities. By comparing the scaling relations of Mg b and Hβ and central velocity dispersion with the same relation for the edge-on sample of Falcón-Barroso et al. (2002) we derive a picture in which the central regions of Sa galaxies contain at least 2 components: one (or more) thin, disc-like component, often containing recent star formation, and another, elliptical-like component, consisting of old stars and rotating more slowly, dominating the light above the plane. If one defines a bulge to be the component responsible for the light in excess of the outer exponential disc, then many Sa-bulges are dominated by a thin, disc-like component containing recent star formation.

37 potential members of the red-giant branches of NGC 6192, NGC 6208 and NGC 6268 were observed in the UBV system, while 22 of them were also observed in the DDO system. The observations were made at La Silla and Cerro Tololo Inter-American observatories (Chile), using pulse-counting photoelectric photometers. Coravel radial velocities (RVs) were obtained at La Silla for 24 red giant candidates in the three clusters. Five stars of NGC 6192 have RVs in the narrow range -8.8 km/s < VR < -6.4 km/s, including two new spectroscopic binaries (SBs). Three stars of NGC 6208 – including a new SB – and three stars of NGC 6268 show similar RVs so that their physical membership to NGC 6208 and NGC 6268, respectively, is highly probable. Mean radial velocities are: -7.7 ± 0.38 km/s (NGC 6192), -32.21 ± 0.28 km/s (NGC 6208) and -15.11 ± 0.08 km/s (NGC 6268). We have also derived the following mean E(B-V) values from Janes (1977) iterative method: 0.63 ± 0.02 (NGC 6192), 0.31 ± 0.02 (NGC 6208) and 0.43 ± 0.02 (NGC 6268).

We present some preliminary results obtained within the MAGPOP-ITP collaboration for a subsample of four dwarf elliptical galaxies. On the basis of high-resolution, optical spectroscopic data obtained for these galaxies at the WHT, their ages, metallicities and single element abundance ratios have been derived from their line-strength indices and the improved, MILES-based, stellar population model predictions by Vazdekis et al. (in preparation).

The evolution of stellar disks is of great importance for understanding many aspects of galaxy formation. In this work we perform stellar population synthesis on radially resolved photometry of 564 disk galaxies from the SDSS DR5, selected to have both spectra of the central regions and photometry. To explore fully the multi-dimensional likelihood space defined by the output parameters of the spectral synthesis, we use Markov Chain Monte Carlo to quantify the expectation values, the uncertainties and the degeneracies of the parameters. We find good agreement between the parameter values obtained using the SDSS broad-band colors and the spectra respectively. In general the derived mean stellar age and the best-fit stellar metallicity decline in value from the galaxy center to the outer regions (around 1.5 half-light radii), based on sub-samples defined by concentration index. We also find that the radial dependency of the stellar population parameters exhibits a significant variation, and this diversity is likely related to morphology and the physics of star formation.

I present a report of the work in progress towards building a graphical user interface (GUI) for STECKMAP (STEllar Content and Kinematics via Maximum A Posteriori). It is the first serious attempt at making a GUI for a software for analysis of stellar content from integrated spectra of galaxies. It will allow a wider fraction of the community to use this sort of tools thanks to improved user-friendliness. As a result, better understanding of these methods and their strengths and flaws will be achieved by the community. This software also has a strong pedagogical potential. It will contribute to a higher awareness of the community concerning the challenges and the oppportunities in stellar populations modelling. The homepage of the project is http://www.astro.u-strasbg.fr/Obs/GALAXIES/stecmap_eng.html.

We present the result of a search for Cepheids in the Local Group dwarf irregular galaxy (DIG) Pegasus. We identified 20 Cepheid stars with periods 0d.6 < P < 15d.3. We have compared them with previously published Cepheids and we have carried out an accurate completeness analysis in order to obtain the fraction of them which are lost. Using their period-luminosity relation we obtain a distance for Pegasus of 950±30 Kpc.

Multi-object spectrographs available on 8-m class telescopes provide the unique opportunity to directly investigate the kinematical and chemical properties of significant samples of resolved stars in galaxies of the Local Group. We present here the first results concerning an extensive study of stellar populations of the Carina dSph galaxy, based on data collected with the multi-object spectrographs FORS2 and FLAMES, both available at VLT. Preliminary estimates concerning the radial velocity distributions of the different samples are presented.

We present preliminary results of a wide-field spectroscopic study on star clusters in the spiral galaxy M 33. We derive for 42 star clusters both age and metallicity using the principles of the Bayesian statistic and the Lick indices. We find that M 33 globular clusters in our sample are relatively young (∼8 – 9 Gyr), none of them being as old as the oldest Galactic counterparts. This implies that this galaxy started forming most of its star clusters after the main episode of star formation took place in the big Local Group galaxies (Milky Way, M 31 and LMC), possibly together with the SMC.

We present preliminary results from a near-infrared, integral-field study of the central 500 pc in the nearby Sbc spiral NGC 613. More specifically, we present maps of various gaseous emission lines in which the ring structure can be identified. The ring consists of at least seven “hot spots” that are actively forming stars and thus can be identified in recombination lines of hydrogen (H) and Helium (He). The molecular gas (traced by emission from the H2 molecule) is more evenly distributed over the entire ring. We also present H- and K-band spectra of one of the ring hot spots and the nucleus of NGC 613 (i.e. the central 1′′). The nucleus emits little or no flux in H or He recombination lines. Instead, its spectrum is dominated by H2 and [FeII] emission, suggesting that NGC 613 is currently in a phase in which gas is accumulating within the central 50 pc. Moreover, we find clear evidence that the ring structure is disturbed by an energetic outflow from the nucleus, supporting evidence that NGC 613 harbors an AGN.

We present a novel approach for simultaneous extraction of stellar population parameters and internal kinematics from the spectra integrated along a line of sight. We fit a template spectrum into an observed one in a pixel space using a non-linear χ2 minimization in the multidimensional parameter space, including characteristics of the line-of-sight velocity distribution (LOSVD) and parametrized star formation history (SFH). Our technique has been applied to IFU and multi-object spectroscopy of low-luminosity early type galaxies.

We present new near-infrared Ks photometry of the interesting Galactic globular cluster NGC 6441. The optical-NIR color-magnitude diagram shows evolutionary features that seem to agree with a canonical evolutionary framework. The K-band Period-Luminosity-Metallicity relation of RR Lyrae stars gives a distance estimate of 15.51±0.07 that is slightly larger previous estimates.

We present new results on stellar populations of bulges in spiral galaxies, from optical and near-IR data (images and spectra). In particular, we analyze a sample of bulges hosted by low surface brightness galaxies (LSBs). Correlations between metallicity, scale lengths of disk and bulges, and HI content are reported, supporting the bulge secular evolution hypothesis, as well as systematics between the derived evolutionary parameters of the embedded stellar populations. Using spectra of moderate resolution, we also investigate the stellar histories of bulges using Lick/IDS indices and recent α-enhancement models. Results indicate that small bulges tend to be smaller and metal poor, compared to larger ones. However, all bulges appear to have been formed in the same time-scale. We present some ongoing studies and some prospects of our research.