Search

We show how present-day 10 meter class telescopes can provide broadband imaging 1.5-2 mag deeper than most previous results within a reasonable amount of time ( ~ 8h on source integration). We illustrate the ability of the 10.4 m Gran Telescopio de Canarias (GTC) telescope to produce imaging with a limiting surface brightness of 31.5 mag/arcsec2 (3σ in 10 × 10 arcsec boxes). We explore the stellar halos of nearby galaxies obtaining surface brightness radial profiles down to μr ~ 33 mag/arcsec2. This depth is similar to that obtained using star counts techniques of Local Group galaxies, but is achieved at a distance where this technique is unfeasible.

Within the central 10 pc of our Galaxy lies a dense cluster of stars, the nuclear star cluster. This cluster forms a distinct component of our Galaxy. Nuclear star clusters are common objects and are detected in ~ 75% of nearby galaxies. It is, however, not fully understood how nuclear star clusters form. The Milky Way nuclear star cluster is the closest of its kind. At a distance of only 8 kpc we can spatially resolve its stellar populations and kinematics much better than in external galaxies. This makes the Milky Way nuclear star cluster the perfect local reference object for understanding the structure and assembly history of nuclear star clusters in general. There are of the order of 107 stars within the central 10 pc of the Galactic center. Most of these stars are several Gyr old late-type stars. However, there are also more than 100 hot early-type stars in the central parsec of the Milky Way, with ages of only a few Myr. Beyond a projected distance of 0.5 pc of the Galactic center, the density of young stars was largely unknown, since only very few spectroscopic observations existed so far. We covered the central >4 pc2 (0.75 sq.arcmin) of the Galactic center using the integral-field spectrograph KMOS (VLT). We extracted more than 1,000 spectra from individual stars and identified >20 new early-type stars based on their spectra. We studied the spatial distribution of the different populations and their kinematics to put constraints on the assembly history of the Milky Way nuclear star cluster.

Large surveys and follow-up spectroscopic studies in the past few decades have been providing chemical abundance data for a growing number of very metal-poor ([Fe/H] et al. 2013). The effective temperatures of these stars are 4500–5000 K, corresponding to a mass of around 0.5 solar masses. Our standard analysis of the high-resolution spectra based on 1D-LTE model atmospheres has obtained self-consistent chemical abundances for these objects, assuming small values of micro-turbulent velocities compared with giants and turn-off stars. The low temperature of the atmospheres of these objects enables us to measure their detailed chemical abundances. Interestingly, two of the four stars have extreme chemical-abundance patterns: one has the largest excesses of heavy neutron-capture elements associated with the r-process abundance pattern known to date (Aoki et al. 2010), and the other exhibits low abundances of the α-elements and odd-Z elements, suggested to be signatures of the yields of very massive stars (> 100 solar masses; Aoki et al. 2014). Although the sample size is still small, these results indicate the potential of very low-mass stars as probes to study the early stages of the Milky Way's halo formation.

We present indirect constraints on the stellar initial-mass-function (IMF) in nine massive elliptical galaxies with σ ≈ 300 km/s, via a comparison of dynamical and stellar-population based stellar masses. We use adaptive-optics assisted, high resolution kinematical data from the SINFONI Search for Supermassive Black Holes that allow us to constrain the dynamical stellar mass-to-light ratio in the very centre of each galaxy. Hence we measure the IMF in a galaxy region where the stellar mass dominates over dark matter, minimising any potential degeneracy between the two mass components. In six of our galaxies – those which have depleted stellar cores – we find an IMF consistent with the one measured in the Milky-Way via direct star counts. The three remaining, power-law galaxies have instead stellar masses about a factor of two times larger than expected from a Milky-Way type IMF, indicating either a more bottom-heavy IMF (like, e.g., the Salpeter IMF) or a dark-matter distribution that is degenerate with the stellar mass down to the very centres of these galaxies. The bottom-light IMF in our core galaxies is surprising in view of previous studies that suggested a systematic IMF variation where early-type galaxies with σ ≈ 300 km/s have a Salpeter or even more dwarf-dominated IMF. Core galaxies are particularly important since their unique central orbital structure offers an independent crosscheck for the dynamical models. Our models with a bottom-light IMF are consistent with the distribution of orbits predicted by SMBH-binary core-formation models. This indicates that spatially well resolved central kinematical data are important for determining unbiased dynamical stellar mass-to-light ratios. Our results imply either that the IMF in massive galaxies varies over a wider range than previously anticipated, and is not the same in core and power-law ellipticals, or else that there are systematic variations in the distribution of dark matter among massive early-type galaxies.

Within the central 10 pc of our Galaxy lies a dense cluster of stars, the nuclear star cluster, forming a distinct component of our Galaxy. Nuclear star clusters are common objects and are detected in ∼75% of nearby galaxies. It is, however, not fully understood how nuclear clusters form. Because the Milky Way nuclear star cluster is at a distance of only 8 kpc, we can spatially resolve its stellar populations and kinematics much better than in external galaxies. This makes the Milky Way nuclear star cluster a reference object for understanding the structure and assembly history of all nuclear star clusters.We have obtained an unparalleled data set using the near-infrared long-slit spectrograph ISAAC (VLT) in a novel drift-scan technique to construct an integral-field spectroscopic map of the central ∼10 × 8 pc of our Galaxy. To complement our data set we also observed fields out to a distance of ∼19 pc along the Galactic plane to disentangle the influence of the nuclear stellar disk.From this data set we extract a stellar kinematic map using the CO bandheads and an emission line kinematic map using H2 emission lines. Using the stellar kinematics, we set up a kinematic model for the Milky Way nuclear star cluster to derive its mass and constrain the central Galactic potential. Because the black hole mass in the Milky Way is precisely known, this kinematic data set will also serve as a benchmark for testing black hole mass modeling techniques used in external galaxies.

IAU Symposium, 9 (S303), ISSN:0074-1809, ISSN:1743-9213

With the precise, nearly-continuous photometry from the Kepler satellite and the sub-milliarcsecond resolving capabilities of the CHARA Array, astronomy is entering a new age for the imaging and understanding of stellar magnetic activity. We present first results from our Guest Observer Program, where 180 single-epoch surface image reconstructions of KIC 5110407 have revealed differential rotation and hints of magnetic activity cycles based on both spot and flare variations. Analysis of our larger, full dataset will establish in unprecedented detail how surface magnetic activity correlates with stellar age and spectral type. In addition to Kepler work, we have harnessed the power of the world's largest infrared interferometer to “directly” image the spotted surfaces of a few of the closest RS CVn systems, allowing a comparison of contemporaneous Doppler and light-curve inversion imaging techniques.

The rapidly-accumulating archives of ground-based and spacecraft data worldwide that are being linked together through the International Virtual Observatory Alliance (IVOA) provide the binary star community with unparalleled opportunities for research. The main databases that are available to the astronomical community through the IVOA are discussed. Data from long-lasting spacecraft missions such as IUE are especially valuable for studying long-term variability. Some examples of current research on close binary stars that is being carried through with UV spectra from the IUE archive are presented. Included are the search for O-subdwarf companions to bright Be stars and some results from an ongoing investigation of the Double Periodic Variable phenomenon in Algol binaries.

In this review I will present recent results obtained between 2005, which was the last “Be-stars” meeting in Sapporo, and 2010, on the observations of circumstellar disks around active hot stars.

In this article I review measurements of deuterium in the Milky Way.

Over the next 5 years the VVV collaboration (Vista Variable in the Via Lactea) will conduct an extensive survey of the galactic bulge and disk in the near-IR, using the new VISTA telescope. This public survey covers a field of 520 sqr. deg, including not only regions of high star formation, but also 33 known globular clusters and ~350 open clusters. The final product will be a deep IR atlas in 5 passbands for ~109 point sources among which we expect 106 variable stars. These will be produce a 3-D map of the surveyed region using well-understood primary distance indicators such as RR Lyrae stars. The observations will be combined with data from MACHO, OGLE, EROS, VST, Spitzer, HST, Chandra, Integral, and ALMA for a complete understanding of the variable sources in the inner Milky Way. Several important implications for the history of the Milky Way, for globular cluster evolution, for the population census of the bulge and center, and for the pulsation theory will follow from this survey.

The RAdial Velocity Experiment (RAVE) is an ambitious survey to measure the radial velocities, temperatures, surface gravities, metallicities and abundance ratios for up to a million stars using the 1.2-m UK Schmidt Telescope of the Anglo-Australian Observatory (AAO), over the period 2003–2011. The survey represents a big advance in our understanding of our own Milky Way galaxy. The main data product will be a southern hemisphere survey of about a million stars. Their selection is based exclusively on their I–band colour, so avoiding any colour-induced bias. RAVE is expected to be the largest spectroscopic survey of the Solar neighbourhood in the coming decade, but with a significant fraction of giant stars reaching out to 10 kpc from the Sun. RAVE offers the first truly representative inventory of stellar radial velocities for all major components of the Galaxy. Here we present the first scientific results of this survey as well as its second data release which doubles the number of previously released radial velocities. For the first time, the release also provides atmospheric parameters for a large fraction of the second year data, making it an unprecedented tool to study the formation of the Milky Way. Plans for further data releases are outlined.

The Sloan Extension for Galactic Exploration and Understanding (SEGUE) has now been completed. This is one of three surveys that were executed as part of the first extension of the Sloan Digital Sky Survey (SDSS-II), which consist of LEGACY, SUPERNOVA SURVEY, and SEGUE. The SEGUE program has obtained over 3600 square degrees of ugriz imaging of the sky outside the original SDSS-I footprint. The regions of sky targeted for SEGUE imaging were primarily at lower Galactic latitudes (|b| < 35°), in order to better sample the disk/halo interface of the Milky Way. SEGUE also obtained medium-resolution (R = 2000) spectroscopy, over the wavelength range 3800-9200 Å, for over 200,000 stars in 200 selected areas over the sky available from Apache Point, New Mexico. We discuss the determination of stellar atmospheric parameters (Teff, log g, and [Fe/H]) for these stars, and highlight several of the scientific results obtained to date. The proposed second extension of SDSS, known as SDSS-III, will include SEGUE-2, a program to roughly double the numbers of stars with available spectroscopy, as well as APOGEE, a program to obtain high-resolution (R = 20000) near-IR spectroscopy for over 100,000 stars in the disk, bulge and halo populations of the Galaxy. Other massive spectroscopic surveys of interest to Galactic science are also briefly discussed.

Recent data have revealed a clear distinction between the abundance patterns of the Milky Way (MW) thick and thin disks, suggesting a different origin for each of these components. In this work we first review the main ideas on the formation of the thin disk. From chemical evolution arguments we show that the thin disk should have formed on a long timescale. We also show clear signs that the local stellar samples are contaminated by stars coming from inner radii. We then check what would have to be changed in such a model in order to explain the observables in the thick disk. We find that a model in which the thick disk forms on a much shorter timescale than thin disk and with a star formation efficiency of around a factor of 10 larger than that in the thin disk can account for the observed abundance ratio shifts of several elements between thick and thin disk stars. Moreover, the lack of scatter in the abundance ratio patterns of both the thick and thin disks suggest both components to have been formed in situ by gas accretion and not by mergers of smaller stellar systems. Especially for the thick disk, this last constraint becomes a strong one if its metallicity distribution extends to, at least, solar. Finally, we briefly discuss the interplay between present deuterium abundance and present infall rates in connection with the thin disk evolution.

Extremely metal-poor (EMP) stars are thought to be formed in the low-mass protogalaxies as building blocks of the Milky Way and can be probes to investigate the early stage of galaxy formation and star formation in the early universe. We study the formation history of EMP stars in the Milky Way halo using a new model of chemical evolution based on the hierarchical theory of the galaxy formation. We construct the merging history of the Milky Way halo based on the extended Press-Schechter formalism, and follow the star formation and chemical evolution along the merger tree. The abundance trends and number of low-mass stars predicted in our model are compared with those of observed EMP stars. Additionally, in order to clarify the origin of hyper metal poor stars, we investigate the change of the surface metal abundances of stars by accretion of interstellar matter. We also investigate the pre-enrichment of intergalactic matter by the first supernovae.

A review of recent progress relating to Wolf-Rayet (WR) stars is presented. Topics include improved Milky Way statistics from near-IR surveys, different flavours of hydrogen-rich and hydrogen-poor WN stars, WR masses from binary orbits, plus spectroscopic analysis of WR stars resulting in stellar temperatures, luminosities, ionizing fluxes, plus wind properties accounting for clumping. Chemical abundances of WN and WC stars are presented, including a discussion of neon abundances in WC and WO stars fromSpitzerobservations. Empirical evidence supporting metallicity-dependent winds is also presented, including its effect on subtype distributions in different environments. Finally, difficulties in comparisons between evolutionary models and observations are highlighted, plus outstanding issues with predictions from continuous star formation and instantaneous bursts in the Milky Way

High-resolution adaptive optics observations of the inner 0.5 pc of the Milky Way with multiple intermediate band filters are presented. From the images, stellar number counts and a detailed map of the interstellar extinction were extracted. The extinction map is consistent with a putative southwest-northeast aligned outflow from the central arcseconds.An azimuthally averaged, crowding and extinction corrected stellar density profile presents clear evidence for the existence of a stellar cusp around Sgr A*. Several density peaks are found in the cluster that may indicate clumping of stars, possibly related to the last epoch of star formation in the Galactic Center. An analysis of stars in the brightness range 14.25 < magK < 15.75 shows possible signs of mass segregation.

Star formation at very low metallicity is expected to produce only massive stars. This is a result of the low cooling rate. Hydrodynamical simulations of star formation from zero metallicity gas suggest that the first stars had masses in excess of about 10 2 M [odot ] . These stars can not be observed because of their large redshift and their very short lifetime. However, a similar (but not the same) effect might be observable in regions of star formation close to very luminous radiation sources, where intense radiation may destroy dust and CO molecules in starforming clouds. Such clouds will be warmer than in normal metal rich star forming regions because of the reduced cooling, which is then predominantly due to H 2 and atomic C and O. Under those conditions star formation may result in the formation of high mass stars without the normal large numbers of accompanying low mass stars. Observations show that this process may occur close to the centre of the interacting galaxy M51, where the intense radiation of the nuclear starburst and the small dust content destroyed molecular CO in star forming regions. HST observations of this region show the presence of about 30 massive stars, of $25\textlessM\textless 150 M\odot$ , without the accompanying clusters of low mass stars.

We present results of a photometric survey for carbon stars in the M31 dwarf spheroidal galaxies. From the low frequency of carbon stars in these galaxies compared to their Milky Way cousins we conclude that they consist of predominantly ancient stellar populations. However, the complexity and variety of the metallicity distributions in the M31 dwarf spheroidals suggest that they still experienced an extended epoch of star formation.

We present spectroscopic analysis of ∼1000 stars on the Lick, Keck and AAT planet search projects. This analysis provides a quantitative, and unbiased correlation between metallicity and the rate of occurrence of detected gas giant planets with orbital periods shorter than three years. As stellar metallicity increases, the occurrence of planets increases. Stars with [Fe/H] that is one third of solar only have gas giants detected ∼ 3% of the time. Stars with solar metallicity have a planet occurrence rate of 5 − 10%. The occurrence of gas giant planets rises to 20% in stars with a metallicity that is three times solar.At issue is whether the quantitative dependence of planet occurrence on metallicity is primarily an initial condition, or a by-product of accretion of gas-depleted material onto the convective zone of the star. Accretion could be distinguished as the underlying mechanism for enhanced metallicity if: 1) planet-bearing F-type stars with thinner convective envelopes show a higher mean metallicity than planet-bearing G- or K-type stars, or 2) planet-bearing sub-giants with diluted convective zones showed statistically lower metallicity than their main sequence counterparts.

I summarize the method commonly used to estimate the current star formation rate per unit volume as a function of redshift from various star formation diagnostics, as well as the often conflicting results from the various multi-wavelength datasets collected in recent years. Combined together, and with the help of theoretical and empirical models, these results allow us to address the issues of excitation, reddening, metallicity, and star formation history in individual galaxies at low redshift. They seem to point to the fact, that a lot of the star formation in the local universe, and potentially at all redshift, occurs in burst mode rather than continuously.

Using the circumstellar envelope parameters (mean temperature, extent and opacity) derived by fitting theoretical energy distributions to those observed in a sample of 20 Be stars, we estimate the respective magnitude difference ΔV = V – V* of the continuum flux excess produced by their circumstellar envelopes. Using then the HIPPARCOS parallaxes of these stars and the ISM E(B-V) colour excesses derived with the surrounding normal B stars, we estimate the visual absolute magnitude of the central objects in the program Be stars. In most cases the results obtained are in good agreement with the absolute magnitudes obtained from the photospheric (λ1, D) components derived in the BCD spectrophotometric system. There are, however, strong discrepancies in 4 program stars which deserve further studies. The magnitude excess seems to be ΔV ≲ 0 for the higher effective temperatures only. There is no correlation between ΔV and Vsin i, as would be expected if the circumstellar envelopes were strongly flattened.

To study effects of stellar variability, it is necessary to have complete lists of variable stars with good coordinates, correct variability ranges, reliable classification. The General Catalogue of Variable Stars (GCVS) is one of the main sources of information of this kind. Recently, the flow of information on stellar variability has increased strongly, requiring new approaches to GCVS compilation. New classification schemes are needed for variable stars, taking into account the development of our knowledge. We present information on the current state of the GCVS, its web data base, new Name-Lists containing thousands of new variables. We also discuss the problems of developing a new classification system for variable stars, of implementing catalogs of variable stars based on automatic surveys into the GCVS, of cooperation and interaction between the GCVS and other important sources of information on variable stars.

We advance some results of our study of the star formation history of the Local Group dSph galaxy Leo I, obtained through the analysis of its deep HST color-magnitude diagram (CMD) using model CMDs computed from stellar evolutionary models. We conclude that most star formation (≃ 90%) took place in Leo I between 7 and 1 Gyr ago. It seems to have started at a very low rate ≃ 15 Gyr ago and continued, also at a very low rate, from 1 Gyr ago until the present time. A constant Z=0.0004 and a large fraction of binary stars are required to obtain the best agreement with both the distribution of stars across the CMD and with its morphology. An IMF like the one obtained by Kroupa et al. (1993) for the solar neighborhood, or steeper, is compatible with the data.

We report on our new photometric surveys of star fields in the Fornax dwarf spheroidal (dSph) galaxy designed to investigate its star formation and chemical evolution histories.

Our systematic searches for carbon stars in the Fornax dwarf spheroidal galaxy at the Canada-France-Hawaii Telescope have led to more than a doubling of the number of carbon stars known in this system, to 104. Furthermore, low-luminosity carbon stars resembling those we had previously found in the Small Magellanic Cloud have been identified in this system. We review the carbon star surveys carried out in the Fornax dwarf and present our main results. The Fornax carbon star population is compared to those of other Galactic halo dwarf systems.

HST V, I color-magnitude diagrams (CMDs) of four outer-halo clusters, NGC 2419, Pa13, Pal4 and Eridanus, provide insight into the relative ages of old star clusters throughout the 200 kpc diameter volume sampled, and thus into the formation epoch of the Milky Way galaxy.

This review concentrates on the oldest populations in the LMC. Specifically, the LMC has a large extent and mass, it has star clusters coeval with those in the Milky Way halo, and more work needs to be done before we are convinced that there are similarly-aged field stars in the LMC. Further, all studied fields in the Clouds are different from Milky Way halo fields. Observations with the new generation of large telescopes can clear up the uncertainties noted in this review.

High dispersion spectra for 44 southern evolved stars of spectral type K or M have been obtained. From these observations relative radial velocities of 50 m/s precision have been obtained by the method of digital cross-correlation. This method of achieving precise relative radial velocities for late-type stars, and the problems encountered in its use, are discussed. Using this method, statistically significant radial-velocity variations have been found. Two of the observed stars have their precise radial velocities presented and the potential mechanisms of their variation examined.

In this work, we present a set of M-type star candidates selected from the LAMOST DR1. A discrimination method with the spectral index diagram is used to separate M giants and M dwarfs. Then, we have successfully assembled a set of M giants templates from M0 to M6, using the spectra identified from the LAMOST spectral database. After combining the M dwarf templates in Zhong et al. (2015a) and the new created M giant templates, we use the M-type spectral library to perform the template-fit method to classify and identify M-type stars in the LAMOST DR1. A catalog of M-type star candidates including 8639 M giants and 101690 M dwarfs/subdwarfs is provided. As an additional results, we also present other fundamental parameters like proper motion, photometry, radial velocity and spectroscopic distance.

Throughout the past decade, significant advances have been made in the size and scope of large-scale spectroscopic surveys, allowing for the opportunity to study in-depth the formation history of the Milky Way. Using the fourth data release of the RAdial Velocity Experiment (RAVE), we study the age-metallicity-velocity space of ~ 100,000 FGK stars in the extended solar neighborhood in order to explore evolutionary processes. Combining these three parameters, we better constrain our understanding of these interconnected, fundamental processes.

Kim 1 & 2 are two new star clusters discovered in the Stromlo Missing Satellite Survey. Kim 1, located at a heliocentric distance of 19.8 ± 0.9 kpc, features an extremely low total luminosity (MV = 0.3 ± 0.5 mag) and low star concentration. Together with the large ellipticity (ε = 0.42 ± 0.10) and irregular isophotes, these properties suggest that Kim 1 is an intermediate mass star cluster being stripped by the Galactic tidal field. Kim 2 is a rare ultra-faint outer halo globular cluster located at a heliocentric distance of 104.7 ± 4.1 kpc. The cluster exhibits evidence of significant mass loss such as extra-tidal stars and mass-segregation. Kim 2 is likely to follow an orbit confined to the peripheral region of the Galactic halo, and/or to have formed in a dwarf galaxy that was later accreted into the Galactic halo.

Large complexes of young objects are common features in galaxies and are called superassociations, complexes and supercomplexes according to their size. They contain HII regions, early-type stars, associations and young clusters. Such large structures are expected to trace the star formation regions within galaxies. Star counts and spectral classification over extended areas, using direct and objective prism Schmidt telescope plates are good methods of determining the boundaries of these complexes and supercomplexes where the spatial density of early-type stars is enhanced. A project of tracing the supercomplexes in the Magellanic Clouds has started using plates taken with the UK 1.2 m Schmidt Telescope.

The He-rich variable HD 37479 has 2 axes of symmetry, one characterized by the depletion of metals, and one by the enrichment of He. The former is oriented along the axis of the magnetic dipole, while the latter is off set by some 45°. The 2 axes represent 2 different modes of diffusion, the first one being controlled solely by the magnetic field, irrespective of wind, the second one being due to stellar wind that is controlled by the magnetic field and intertial forces. It has been attempted to formulate simple physical conditions that allow to determine the diffusion regions on the surface. It is shown that the resulting surface map can well reproduce the observed phase variations of the equivalent widths of HeI 4471, of UV resonance lines of C IV and Si IV, and the effective magnetic field.

The Star Formation History (SFH) of the Phoenix dwarf galaxy has been obtained using IAC-star and IAC-pop. The observations are based on WFPC2@HST. The results show a Star Formation Rate (SFR) decreasing with time and that star formation has happened in Phoenix up to 0.5 Gyr ago. The metallicity decrease with the stellar age: z >0.0007 for stars younger than 5 Gyr and z N of the star density distribution profile has been obtained as a function of the time. The results show that α N decreases smoothly with time, suggesting a sort of shrinking scenario for the evolution of Phoenix.

1. The data. We study detailed star formation histories (SFH) of 14 dwarf galaxies in the central parts ( 300 Kpc) of the two nearby galaxy groups: M 81 (D=3.6 Mpc) and Cen A (D = 3.8 Mpc). The images of 7 galaxies were selected from the sample of about 50 nearby dwarf galaxies observed with the Advanced Camera for Surveys (ACS) at the Hubble Space Telescope within our prog. 9771 & 10235, (PI I.Karachentsev). The rest of the images (ACS and WFPC2) were taken from the Hubble Archive (prog. 9884, 5898 and 6964). 2. The methods and photometry. Photometry of the resolved stars in the galaxies was made with the DOLPHOT package (Dolphin 2002, MNRAS, 332, 91) for crowded field photometry. Photometric distances for all galaxies in the sample were obtained using tip of the red giant branch (TRGB) distance indicator (Lee et al. 1993, ApJ, 417, 553; Sakai et al. 1996, ApJ, 461, 713). We have developed the StarProbe package for quantitative star formation history determination (Makarov & Makarova 2004, Ap, 47, 229). We create a library of synthetic color-magnitude diagrams from theoretical stellar isochrones, taking the initial mass function, distance to the galaxy, internal and external absorption, and photometric errors into account. The resulting synthetic diagrams are combined linearly and compared quantitatively with photometric data for stars in a galaxy in order to determine star formation rates as a function of age and metallicity.

We present a method for deriving light-weighted stellar metallicities and ages from high-resolution galaxy spectra, based on the new population synthesis code of Bruzual & Charlot (2003). The method relies on the simultaneous fit of several optical spectral absorption features that are sensitive to either age or metallicity, but not to the $\alpha$ -elements abundance ratio. We have constructed a library of stochastic star formation histories, which we have used to derive median-likelihood estimates of ages and metallicities for $\sim10^5$ galaxies extracted from the Sloan Digital Sky Survey Data Release One (SDSS DR1), spanning the full range in star formation activities, from dormant early type to actively star forming. Here we discuss the results for early-type galaxies. We show that the $g-r$ , $M_r$ color-magnitude relation for these galaxies is driven primarily by changes in metallicity and in heavy-element abundance ratios. Changes in light-weighted age contribute mainly to the scatter about the relation. This is consistent with previous interpretations of this relation based on lower resolution models. To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Extensive discoveries of variable stars in ground-based photometric surveys and in observations from space missions that provide unprecedented accuracy demonstrate that, till the most recent time, we knew only a tiny fraction of all detectable variable stars of our Galaxy. As a result, our knowledge on stellar variability types, related physical processes, variable-star statistics turn out to be based on an unrepresentative sample and are expected to be radically revised in the near future. The flow of new discoveries results in quite difficult problems for catalogs of variable stars, making it impossible to proceed in their compilation in the traditional way. Regretfully, automatic solutions are still not completely satisfying. Though not able to suggest a perfect way out, we present our vision of the future of variable-star research.

The present study reports measurements of the rotation period of a young solar analogue, estimates of its surface coverage by photospheric starspots and of its chromospheric activity level, and derivations of its evolutionary status. It compares the chromospheric activity level of this young star with a model of chromospheric activity evolution established by combining relationships between the R′HK index and the Rossby number with a recent model of stellar rotation evolution on the main-sequence.

The massive star forming complex W33 contains several molecular clouds at different stages of star formation activity, ranging from quiescent to highly active clouds. Our trigonometric parallax observations of water masers in this complex, conducted with the VLBA at 22.2 GHz, show that all water masers have the same distance of 2.4 kpc, locating the W33 complex in the Sagittarius spiral arm.

Photometric searches for Be stars in environments with different metallicities have led to the discovery of many Be-like star variables. The knowledge of these types of variables is still fragmentary. This work presents the preliminary results of analyzing FLAMES+GIRAFFE spectra of a sample of these Be-like stars that we have found in the Small Magellanic Cloud (SMC).

We have developed a new procedure to search for Carbon-Enhanced Metal-Poor (CEMP) stars from the Hamburg/ESO (HES) prism-survey plates. This method uses an extended line index for the CH G-band, which we demonstrate to have superior behavior when compared to the narrower G-band index formerly employed for these spectra.A first subsample, biased towards brighter stars (B

We have carried out a multi-wavelength study of the star forming region NGC 1893 to make a comprehensive exploration of the effects of massive stars on low mass star formation. Using deep optical U BV RI broad band, Hα narrow band photometry and slit-less spectroscopy along with archival data from the surveys such as 2MASS, MSX, IRAS and NVSS, we have studied the region to understand the star formation scenario in the region.

We present TCS-CAIN, a NIR survey of the Galactic plane, recently made public at the Instituto de Astrofisica 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.

Despite much work, the connection between dwarf elliptical galaxies (dEs) and dwarf irregulars (dIs) remains unclear. Recently, we found that the surface brightness profiles (SBPs) of dIs in the near-infrared can be well fitted with a hyperbolic secant (sech) function. From sech fits, a tight relationship was derived between the absolute magnitude, central surface brightness, and 21cm line widths, which amounts to a fundamental plane for dIs. Here we examine how closely dEs fit into the dI fundamental plane using published data for 22 dEs in the Virgo cluster and the Local Group. Over a 9 mag interval in absolute magnitude the dEs fall in the plane defined by the dIs. The outstanding overlap suggests more than a casual relationship between the two classes., Comment: To appear in the Proceedings of the IAU Colloquium 198, H. Jerjen & B. Binggeli

The currently available empirical evidence on the star formation processes in the extreme, high-pressure environments induced by galaxy encounters, mostly based on high-resolution Hubble Space Telescope imaging observations, strongly suggests that star cluster formation is an important and perhaps even the dominant mode of star formation in the starburst events associated with galaxy interactions.

We present new medium-deep wide field galaxy counts at J- and K-bands, performed in the ELAIS fields. The source detection limits are at J = 19.5 and K = 18.0 magnitudes. The sky coverage is 1 degree2, making our survey the largest to date at these wavelengths and magnitudes. Counts in this brightness range are critical for normalization of models when explaining the deepest galaxy counts. In our survey fields we find evidence for a higher than expected local galaxy density. If normalized to our counts, galaxy models do not need strong brightness evolution or exotic populations to be explained even at the faintest levels. We measure clearly sub-Euclidean slopes of d log N(m)/dm ~ 0.45 to 0.50 at 13 < K < 17.5 and 14.5 < J < 19. Normal, passively evolving stellar populations along with a high normalization of the local luminosity function and an open cosmological model best fit both the slope and amplitude of our number counts. We report a preliminary value, ~ 30 n Wm−2sr−1, for the K-band extragalactic background light using zodi-subtracted DIRBE-data and our observed star counts. The value is consistent with, e.g., Matsumoto (these Proceedings 2001) and Gorjian, V., Wright, E. L., & Chary, R. R. 2000, ApJ, 536, 550, but is considerably higher than extrapolations from faint galaxy counts.

By isolating the red clump giant population in the color-magnitude diagrams and inverting their star counts, we can obtain directly the density distribution of the old stellar population along the line of sight. We have applied this method to several near infrared surveys and obtained information on the disc, bulge and long bar. The disc is well fitted by an exponential distribution in both the galactocentric distance and height, flared and warped in the outer parts, and with a deficit of stars in the inner in-plane regions. The long bar occupies these in-plane regions within R < 3.9 kpc, with approximate dimensions of 7.8 kpc × 1.2 kpc × 0.2 kpc and a position angle of 40-45 deg. The bulge is a triaxial structure, possibly boxy, thicker and shorter than the long bar and with position angle of 10-30 deg.