The integrated light of open cluster remnants (OCRs) is expected to be similar to that of open clusters of comparable ages. Despite erosion of the mass function in remnants as a consequence of dynamical evolution, their integrated spectra could still be similar to those of the clusters of comparable age as long as a sufficient number of bright stars remain. In the present work we employ integrated spectroscopy and individual spectra of stars to analyze 8 OCRs and candidates which were previously classified as open clusters and a new unclassified object. The OCRs and possible open cluster remnants (POCRs) are underpopulated with respect to usual open clusters, but they show a significant density contrast of bright stars when compared to the Galactic field. The spectroscopic observations were carried out with the 2.15-m telescope at CASLEO (San Juan, Argentina) in the range 3800-6800 Å, during 2003 and 2004. We derive foreground interstellar reddening values and ages. We find in most of the sample that the derived properties are compatible with what should be expected for OCRs.

The Small Magellanic Cloud (SMC) is the only dwarf galaxy in the Local Group that is known to have formed and preserved populous star clusters continuously over the past 12 Gyr. Due to its proximity (≈ 60 kpc), stars can be resolved well below the oldest main sequence turnoff points. This facilitates accurate age and metallicity determinations without suffering from the age-metallicity degeneracy. Therefore, the SMC star clusters provide a unique closely spaced set of single-age, single-metallicity tracers to derive a well-sampled age-metallicity relation required for the understanding of the star formation history of this satellite galaxy. Up to date spectroscopically based metallicity estimates exist only for the small number of 7 clusters (Da Costa & Hatzidimitriou 1998). Our project now more than doubles the available data set by the observation of 10 additional clusters.

We analysed HST/WFPC2 colour-magnitude diagrams (CMDs) from 15 populous Large Magellanic Cloud (LMC) stellar clusters with ages between ∼0.3 Gyr and ∼3 Gyr. These (V, B-V) CMDs are photometrically homogeneous and reach typically V ∼22. Accurate and self-consistent physical parameters (age, metallicity, distance modulus and reddening) were extracted for each cluster by comparing the observed CMDs with synthetic ones. These determinations were made by means of simultaneous statistical comparison of MS fiducial lines and red clump position, offering objective and robust criteria to determine the best models. In general, the best models show a satisfactory fit to the data, adequately constraining the physical parameters of each cluster. The inferred spatial distribution of these clusters is roughly aligned with the LMC disk. The set of ages and metallicities homogeneously derived here can be used to calibrate integrated light studies applied to distant galaxies.

We describe our results on multi-colour observations of extremely red galaxies found in two gravitational lensing clusters (Abell 1835 and AC114). Applying a colour criteria of R-K≥ 5.6 we have selected 12(10) EROs, of which 10(4) have no R-band detection. 5 of these objects have exceptional red colours (R-K>7.5). We compare their colours with other galaxy populations, like distant red galaxies and infrared detected extremely red galaxies, in order to differentiate between them.

We present TCS-CAIN, a NIR survey of the Galactic plane, recently made public at the Instituto de Astrofísica de Canarias, and some results derived from it: with star counts derived directly from it the structure of the inner the Milky Way can be dissected, and with low resolution spectra, (part of a follow-up program), its nature, specifically the metallicity distribution in the inner 4 kpc of the Galaxy, further understood.

In this proceeding we present the procedure that we have adopted to obtain a dataset of Padova94 tracks (Bressan et al. (1993), Fagotto et al. (1994), Fagotto et al. (1994)) interpolated in metallicity. The procedure requires special care to avoid spurious features in the resulting grid, thus we have subdivided tracks in evolutionary phases, we have chosen the suitable interpolation method and the transition masses. Finally, we have compared our interpolated dataset with a similar models, Girardi et al. (2000), obtaining a general good agreement.

We have derived a new Hβ absorption index definition, which is fully optimized as an age indicator for old and intermediate-aged stellar populations. Rather than using stellar spectra, we employed theoretical SEDs at moderately high resolution for simple stellar populations of different ages and metallicities. The new index, which is virtually insensitive to metallicity, provides us with improved abilities for lifting the age-metallicity degeneracy, that affects the standard Hβ Lick/IDS index definition. Among other advantages this new index does not require spectra of extremely high signal-to-noise and it can be easily applied to observations of faint galaxies or surveys data.

Using subspace methods, we study the distribution of physical components of galaxies in wavelength space. We find that it is valid to assume that the stellar and the gaseous components of galaxies span complementary subspaces. To first order, stellar and gaseous spectral features can be extracted from galaxy spectra through a simple matrix multiplication. By comparing the stellar continua obtained respectively using the model-based and the empirical approach through a commonality measure, we conclude that the latter may lose higher-order spectral features.

We present a star cluster population study in the interacting galaxy system M51 based on HST ACS BV I mosaic images taken by the Hubble Heritage Team to commemorate the HST's 15th anniversary. We have found and classified star clusters in M51 using SExtractor and visual inspection. We have derived the photometry, size, and age of the clusters. It is found that the companion SB0 galaxy NGC 5195 harbors about 50 faint fuzzy clusters and that the age distribution of star clusters appears to be correlated with the epochs of dynamical events in M51 system.

Spiral galaxies can be affected by interactions in clusters, that also may distort the internal velocity field. If unrecognized from single-slit spectroscopy, this could lead to a wrong determination of the maximum rotation velocity as pointed out by Ziegler et al. 2003. This parameter directly enters into the Tully--Fisher relation, an important tool to investigate the evolution of spiral galaxies. To overcome this problem, we measure the 2D-velocity fields by observing three different slit positions per galaxy using FORS2 at the VLT providing us with full coverage of each galaxy and an adequate spatial resolution. The kinematic properties are compared to structural features determined on the HST/ACS images to assess possible interaction processes. As a next step, the whole analysis will be performed for three more clusters, so that we will be able to establish a high-accuracy TFR for spirals at z∼0.5.

Understanding the stellar populations of extragalactic globular cluster (GC) systems and, in particular, determining their ages, provide essential clues to constrain the star formation histories of their host galaxies. We here summarize the most relevant results derived from a detailed, spectroscopic study of 20 GCs in the E0 NGC 1407. We find most GCs are old (~11 Gyr), follow a tight metallicity sequence reaching values slightly above solar, and exhibit mean [α/Fe] ratios of ~0.3 dex. Blue horizontal branch effects are detected for 3 GCs. We also report the existence of two families of metal-rich (MR) GCs, as some of them exhibit significantly larger [Mg/Fe] and [C/Fe] ratios, what might be interpreted in terms of different star formation time-scales. Striking CN overabundances are found over the entire GC metallicity range. In particular, for MR GCs, N increases dramatically while C essentially saturates. This may be interpreted as a consequence of the increasing importance of the CNO cycle with increasing metallicity.

The star formation history (SFH) of Local Group galaxies is a powerful tool for studying their evolution, including chemical enrichment histories and stellar population gradients, which in turn may shed light on the role of reionization or Supernovae feedback in galaxy formation and evolution. In particular, isolated dwarfs are ideal laboratories since their evolution has not been complicated by the vicinity of giant galaxies. In this paper, we present the project Local Cosmology from Isolated Dwarfs (LCID), aimed at deriving detailed SFHs for a sample of Local Group isolated dwarf galaxies. To accomplish this goal we have collected, using the ACS on board the HST, color-magnitude diagrams (CMD) reaching their oldest main sequence turnoff (V≃ 28 or MV ≃ + 3.5) with good photometric accuracy. Some preliminary results from the CMDs are shown and briefly discussed.

The theory interest group in the International Virtual Observatory Alliance (IVOA) has the goal of ensuring that theoretical data and services are taken into account in the IVOA standards process. In this poster we present some of the efforts carried out by this group to include evolutionary synthesis models in the VO framework. In particular we present the VO tool PGos3, developed by the INAOE (Mexico) and the Spanish Virtual Observatory which includes most of public SSP models in the VO framework (e.g. VOSpec). We also describe the problems related with the inclusion of synthesis models in the VO framework and we try to encourage people to define the way in which synthesis models should be described. This issue has implications not only for the inclusion of synthesis models in the the VO framework but also for a proper usage of synthesis models.

HST observations have revealed that compact sources exist at the centers of many, maybe even most, galaxies across the Hubble sequence. These sources are called “nuclei” or also “nuclear star clusters” (NCs), given that their structural properties and position in the fundamental plane are similar to those of globular clusters. Interest in NCs increased recently due to the independent and contemporaneous finding of three groups (Rossa et al. for spiral galaxies; Wehner & Harris for dE galaxies; and Côté et al. for elliptical galaxies) that NC masses obey similar scaling relationships with host galaxy properties as do supermassive black holes. Here we summarize the results of our group on NCs in spiral galaxies. We discuss the implications for our understanding of the formation and evolution of NCs and their possible connection to supermassive black holes.

We summarize results from McDermid et al. (2006), who present a set of follow-up observations of the sauron representative survey of early-type galaxies. We used the oasis integral-field spectrograph (while at the Canada-France-Hawaii Telescope) to obtain high spatial resolution spectra of 28 elliptical and lenticular galaxies. These seeing-limited data have on average twice the spatial resolution of the sauron data, albeit over a smaller field. These new data reveal previously unresolved features in these objects' stellar kinematics, stellar populations, and ionized gas properties. In this contribution, we focus on the discovery of a population of compact kinematically decoupled cores in a number of our sample galaxies. These compact cores are related to regions of young stars, and counter-rotate around the host galaxy's minor axis. We compare these objects to previously known decoupled components, which in contrast are composed of old stars, and which rotate around axes unrelated to the host galaxy's kinematics or shape. A key difference between these two kinds of decoupled cores are their physical size and relative mass. The compact decoupled cores are smaller than a few hundred parsec, and constitute less than a few percent of the total galaxy mass. The ‘classical’ decoupled cores exist on kiloparsec scales, and comprise around a factor 10 more mass. We suggest that the small components are only found with young ages because of their low mass-to-light ratio. We show that after a few Gyrs, these components ‘fade’ into the background galaxy, making them more difficult to detect. We draw the following conclusions: 1) young stars found in early-type galaxies are very often associated with centrally-concentrated counter-rotating components; 2) the small mass fraction and kinematic decoupling of these cores suggests that the star formation is associated to minor accretion events, which effectively drive the spread in luminosity-weighted ages found in early-type galaxies; and 3) such decoupled components may be common in all early-type galaxies, but not directly observed due to their small contribution to the total galaxy light at older ages.

The IMF UNIVERSALITY HYPOTHESIS cannot be discarded despite the existence of the CLUSTER IMF THEOREM. This means that the currently existing star-formation theory fails to describe the stellar outcome. The IGIMF THEOREM, however, predicts a variation of galaxy-wide IMFs in dependence of the galaxy's star-formation rate even if the IMF UNIVERSALITY HYPOTHESIS is valid. Taking indirect evidence from chemical evolution studies and the IGIMF THEOREM into account, it follows, however, that bulges and elliptical galaxies may have had a top-heavy IMF. A break-down of the IMF UNIVERSALITY THEOREM would thus be evident in extreme galaxy-wide (≳ 10 M⊙yr) star-formation events.

Properties related to dust attenuation and star formation of an UV selected sample of intermediate redshift galaxies are presented in this work. We find hints of a decrease of the LIR/LFUV ratio with increasing redshift at low values of the total luminosity. Downsizing is observed at all redshifts, and the SSFR is found to increase with increasing redshift at all stellar masses.

We present a new method for measuring the recent star formation history (SFH) of galaxies from their 4000Å break and Balmer absorption line strength. By making use of the whole 3750-4150Å spectral region, the method achieves a higher signal-to-noise ratio than traditional indices. The new technique is ideally suited to finding evidence for weak or old starbursts in good quality spectra, or studying post-starburst galaxies at high redshift. On application to massive, bulge dominated galaxies in the SDSS, we find clear correlations between the recent star formation history of bulges and the properties of the AGN.

It is well established that mass loss from AGB stars due to dust driven winds cannot be arbitrarily low. We model the mass loss from carbon rich AGB stars using detailed frequency-dependent radiation hydrodynamics including dust formation. We present a study of the thresholds for the mass loss rate as a function of stellar parameters based on a subset of a larger grid of such models and compare these results to previous theoretical work. Furthermore, we demonstrate the impact of the pulsation mechanism and dust formation for the creation of a stellar wind and how it affects these thresholds and briefly discuss the consequences for stellar evolution.

Recent (≤ 0.5 Gyr) star formation histories have a large impact on the observable properties of galaxies. Using HST/ACS observations, we have used the blue helium burning (BHeB) stars to construct spatially resolved star formation histories of M81 group dwarf galaxies with a time resolution of roughly 30 Myr over the last 500 Myr. We have designed a sample of ten galaxies spanning ranges of 6 magnitudes in luminosity, 1000 in current star formation rate, and 0.5 dex in metallicity. The ACS observations allow us to directly observe the strength and spatial relationships of all of the recent star formation in these galaxies. These observations are complemented by high-quality ancillary data (e.g., Spitzer, UV/optical/H-alpha/NIR, VLA HI). Our resolved star formation maps will be compared with star formation rates inferred from H-alpha, UV, and IR observations – allowing an independent calibration of these techniques. Given the ranges in metallicity, these observations will provide calibrations of stellar evolution tracks for young, low metallicity stars. These observations will also enable us to construct prescriptions of how star formation and feedback depend on metallicity, size, gas content, and current star formation rates in galaxies. Finally, I note that the new observations becoming available as a part of the ANGST (ACS Nearby Galaxies Survey Treasury Program) will allow a large number of dwarf galaxies to be analyzed in this way.