bluuebunny/crossref_metadata_2025 huggingface dataset:
Roll convection of binary fluid mixtures in porous media
Authors: UMLA R. , AUGUSTIN M. , HUKE B. , LÜCKE M.
Published: April 2010

We investigate theoretically the nonlinear state of ideal straight rolls in the Rayleigh–Bénard system of a fluid layer heated from below with a porous medium using a Galerkin method. Applying the Oberbeck–Boussinesq approximation, binary mixtures with positive separation ratio are studied and compared with one-component fluids. Our results for the structural properties of roll convection resemble qualitatively the situation in the Rayleigh–Bénard system without porous medium except for the fact that the streamlines of binary mixtures are deformed in the so-called Soret regime. The deformation of the streamlines is explained by means of the Darcy equation which is used to describe the transport of momentum. In addition to the properties of the rolls, their stability against arbitrary infinitesimal perturbations is investigated. We compute stability balloons for the pure fluid case as well as for a wide parameter range of Lewis numbers and separation ratios that are typical for binary gas and fluid mixtures. The stability regions of rolls are found to be restricted by a crossroll, a zigzag and a new type of oscillatory instability mechanism, which can be related to the crossroll mechanism.
Bedforms in a turbulent stream: formation of ripples by primary linear instability and of dunes by nonlinear pattern coarsening
Authors: FOURRIÈRE ANTOINE , CLAUDIN PHILIPPE , ANDREOTTI BRUNO
Published: April 2010

It is widely accepted that both ripples and dunes form in rivers by primary linear instability; the wavelength of the former scaling on the grain size and that of the latter being controlled by the water depth. We revisit here this problem in a theoretical framework that allows to give a clear picture of the instability in terms of dynamical mechanisms. A multi-scale description of the problem is proposed, in which the details of the different mechanisms controlling sediment transport are encoded into three quantities: the saturated flux, the saturation length and the threshold shear stress. Hydrodynamics is linearized with respect to the bedform aspect ratio. We show that the phase shift of the basal shear stress with respect to the topography, responsible for the formation of bedforms, appears in an inner boundary layer where shear stress and pressure gradients balance. This phase shift is sensitive to the presence of the free surface, and the related effects can be interpreted in terms of standing gravity waves excited by topography. The basal shear stress is dominated by this finite depth effect in two ranges of wavelength: when the wavelength is large compared to the flow depth, so that the inner layer extends throughout the flow, and in the resonant conditions, when the downstream material velocity balances the upstream wave propagation. Performing the linear stability analysis of a flat sand bed, the relation between the wavelength at which ripples form and the flux saturation length is quantitatively derived. It explains the discrepancy between measured initial wavelengths and predictions that do not take this lag between flow velocity and sediment transport into account. Experimental data are used to determine the saturation length as a function of grain size and shear velocity. Taking the free surface into account, we show that the excitation of standing waves has a stabilizing effect, independent of the details of the flow and sediment transport models. Consequently, the shape of the dispersion relation obtained from the linear stability analysis of a flat sand bed is such that dunes cannot result from a primary linear instability. We present the results of field experiments performed in the natural sandy Leyre river, which show the formation of ripples by a linear instability and the formation of dunes by a nonlinear pattern coarsening limited by the free surface. Finally, we show that mega-dunes form when the sand bed presents heterogeneities such as a wide distribution of grain sizes.
An experimental study of turbulent vortex rings during their early development
Authors: GAN L. , NICKELS T. B.
Published: April 2010

In this paper, the early development of turbulent vortex rings at two Reynolds numbers is studied using two-dimensional and stereoscopic particle image velocimetry (PIV). In the late 1980s, a similarity theory of turbulent vortex rings was proposed and this theory was tested primarily using laser Doppler velocimetry (LDV). However, because of limitations of the experimental technique, the tests were inconclusive and important assumptions could not be checked. Because single-point measurements were used, vortex ring structures could only be inferred using a complex signal analysis technique. In this study, the PIV technique provides spatial measurements of the full field of the cross-section of a ring from which a more rigorous investigation of the similarity theory is possible. Because the region over which the similarity theory appears to hold starts at about 2.5 orifice diameters downstream, this study focusses on the early development region from this point to 8 diameters downstream. Finally, Reynolds stresses and turbulence production contours are presented. The effects of ring dispersion on the measurements is also studied and quantified.
Scaling of near-wall turbulence in pipe flow
Authors: HULTMARK MARCUS , BAILEY SEAN C. C. , SMITS ALEXANDER J.
Published: April 2010

New measurements of the streamwise component of the turbulence intensity in a fully developed pipe flow at Reynolds numbers up to 145 000 indicate that the magnitude of the near-wall peak is invariant with Reynolds number in location and magnitude. The results agree with previous pipe flow data that have sufficient spatial resolution to avoid spatial filtering effects, but stand in contrast to similar results obtained in boundary layers, where the magnitude of the peak displays a prominent Reynolds number dependence, although its position is fixed at the same location as in pipe flow. This indicates that the interaction between the inner and outer regions is different in pipe flows and boundary layers.
Self-conditioned fields for large-eddy simulations of turbulent flows
Authors: POPE STEPHEN B.
Published: April 2010

An alternative foundation is developed for the large-eddy simulation (LES) of turbulent flows. It is based on ‘self-conditioned fields’, for example, the mean velocity field conditional on a discrete representation of the filtered velocity field. It is shown that the self-conditioned velocity field minimizes the residual kinetic energy, and that, with the ideal model, the method yields the correct one-time behaviour as determined by the Navier–Stokes equations. The approach is extended to the self-conditioned probability density function (PDF) of compositions. Compared to LES formulations based on the filtered velocity and the filtered density function, the self-conditioned field approach has several advantages: for laminar flow, and in the direct-numerical-simulation limit, the residual fluctuations are zero or exponentially small; full account is taken of the probability distribution of turbulent fields; there are no commutation issues; and there are no issues with filtering at walls, where the self-conditioned velocity is zero. The exact evolution equations for the self-conditioned velocity and composition PDF are derived. Basic models are presented, and the development of improved models is discussed.
Self-excited oscillations in three-dimensional collapsible tubes: simulating their onset and large-amplitude oscillations
Authors: HEIL MATTHIAS , BOYLE JONATHAN
Published: April 2010

We employ numerical simulations to explore the development of flow-induced self-excited oscillations in three-dimensional collapsible tubes which are subject to boundary conditions (flow rate prescribed at the outflow boundary) that encourage the development of high-frequency oscillations via an instability mechanism originally proposed by Jensen & Heil (J. Fluid Mech., vol. 481, 2003, p. 235). The simulations show that self-excited oscillations tend to arise preferentially from steady equilibrium configurations in which the tube is buckled non-axisymmetrically. We follow the growing oscillations into the large-amplitude regime and show that short tubes tend to approach an approximately axisymmetric equilibrium configuration in which the oscillations decay, whereas sufficiently long tubes develop sustained large-amplitude limit-cycle oscillations. The period of the oscillations and the critical Reynolds number beyond which their amplitude grows are found to be in good agreement with theoretical scaling estimates.
Linear spatio-temporal instability analysis of ice growth under a falling water film
Authors: HU JUN , ZHOU BING-HONG , HANG YI-HONG , LIU QIU-SHENG , ZHANG SHU-DAO
Published: April 2010

A linear spatio-temporal stability analysis is conducted for the ice growth under a falling water film along an inclined ice plane. The full system of linear stability equations is solved by using the Chebyshev collocation method. By plotting the boundary curve between the linear absolute and convective instabilities (AI/CI) of the ice mode in the parameter plane of the Reynolds number and incline angle, it is found that the linear absolute instability exists and occurs above a minimum Reynolds number and below a maximum inclined angle. Furthermore, by plotting the critical Reynolds number curves with respect to the inclined angle for the downstream and upstream branches, the convectively unstable region is determined and divided into three parts, one of which has both downstream and upstream convectively unstable wavepackets and the other two have only downstream or upstream convectively unstable wavepacket. Finally, the effect of the Stefan number and the thickness of the ice layer on the AI/CI boundary curve is investigated.
Analysis of the dripping–jetting transition in compound capillary jets
Authors: HERRADA M. A. , MONTANERO J. M. , FERRERA C. , GAÑÁN-CALVO A. M.
Published: April 2010

We examine the behaviour of a compound capillary jet from the spatio-temporal linear stability analysis of the Navier–Stokes equations. We map the jetting–dripping transition in the parameter space by calculating the Weber numbers for which the convective/absolute instability transition occurs. If the remaining dimensionless parameters are set, there are two critical Weber numbers that verify Brigg's pinch criterion. The region of absolute (convective) instability corresponds to Weber numbers smaller (larger) than the highest value of those two Weber numbers. The stability map is affected significantly by the presence of the outer interface, especially for compound jets with highly viscous cores, in which the outer interface may play an important role even though it is located very far from the core. Full numerical simulations of the Navier–Stokes equations confirm the predictions of the stability analysis.
Challenges in Stellar Population Studies
Authors: Brinchmann Jarle
Published: April 2010

The stellar populations of galaxies contain a wealth of detailed information. From the youngest, most massive stars, to almost invisible remnants, the history of star formation is encoded in the stars that make up a galaxy. Extracting some, or all, of this information has long been a goal of stellar population studies. This was achieved in the last couple of decades and it is now a routine task, which forms a crucial ingredient in much of observational galaxy evolution, from our Galaxy out to the most distant systems found. In many of these domains we are now limited not by sample size, but by systematic uncertainties and this will increasingly be the case in the future.

The aim of this review is to outline the challenges faced by stellar population studies in the coming decade within the context of upcoming observational facilities. I will highlight the need to better understand the near-IR spectral range and outline the difficulties presented by less well understood phases of stellar evolution such as thermally pulsing AGB stars, horizontal branch stars and the very first stars. The influence of rotation and binarity on stellar population modelling is also briefly discussed.
Blue Stragglers: Spectra of Globular Clusters
Authors: Cenarro A. J. , Cervantes J. L. , Beasley M. A. , Marin-Franch A. , Vazdekis A.
Published: April 2010

The integrated Balmer lines of unresolved stellar systems have been widely used as age indicators, since they are sensitive to the temperature of the main sequence turn-off. However, the existence of “non-canonical” stellar stages such as hot horizontal branch stars and blue straggler stars (BSSs) can lead to underestimations of the true stellar population ages. Using an optimized Hβ index in conjunction with HST/WFPC2 color-magnitude diagrams (CMDs), we find that Galactic globular clusters of similar metallicity exhibit a large scatter in their Hβ strengths, which does not correlate with their CMD-derived ages. Instead, we demonstrate that the specific frequency of BSSs is responsible for the observed Hβ scatter at intermediate-to-high metallicity, in the sense that, at fixed metallicity, higher BSS ratios lead to larger integrated Hβ strengths. Therefore, the specific frequency of BSSs sets a fundamental limit on the accuracy for which integrated spectroscopic ages can be determined for globular clusters and, probably, other stellar systems like galaxies. The observational implications of this result are discussed.
TP-AGB stars in population synthesis models
Authors: Marigo Paola , Girardi Léo , Bressan Alessandro , Aringer Bernhard , Gullieuszik Marco , Held Enrico V. , Groenewegen Martin A.T. , Silva Laura , Granato Gian Luigi
Published: April 2010

In spite of its relevance, the Thermally Pulsing Asymptotic Giant Branch (TP-AGB) phase is one of the most uncertain phases of stellar evolution, and a major source of disagreement between the results of different population synthesis models of galaxies. I will briefly review the existing literature on the subject, and recall the basic prescriptions that have been used to fix the contribution of TP-AGB stars to the integrated light of stellar populations. The simplicity of these prescriptions greatly contrasts with the richness of details provided by present-day databases of AGB stars in the Magellanic Clouds, which are now being extended to other nearby galaxies. I will present the first results of an ongoing study aimed at simulating photometry, chemistry, pulsation, mass loss, dust properties of AGB star populations in resolved and un-resolved galaxies. We test our predictions against observations from various surveys of the Magellanic Clouds (DENIS, 2MASS, OGLE, MACHO, Spitzer, and AKARI). I will discuss the implications and outline the plan of future developments.
Testing evolutionary synthesis models: Empirical feedback to model makers
Authors: Cid Fernandes Roberto , Delgado Rosa M. González
Published: April 2010

Integrated spectra of star clusters are the best test beds for predictions of evolutionary synthesis models. We present spectral fits of star cluster using a variety of recent models. All models allow good spectral fits, but newer ones tend to be better. Ages estimated through spectral fits are not strongly model dependent, but metallicities can differ a lot from one model to another. For some clusters, multi-population fits suggest a combination of very old (1010 yr) and very young (< 108) populations, an artifact of the lack of old and blue stars in the models.
Nebular abundances in galaxies: Beware of biases
Authors: Stasińska Grażyna
Published: April 2010

The derivation of nebular abundances in galaxies using strong line methods is simple and quick. Various indices have been designed and calibrated for this purpose, and they are widely used. However, abundances derived with such methods may be significantly biased, if the objects under study have different structural properties (hardness of the ionizing radiation field, morphology of the nebulae) than those used to calibrate the methods. Special caution is required when comparing the metallicities of different samples, like, for example, blue compact galaxies and other emission line dwarf galaxies, or samples at different redshifts.
Revealing infrared populations of nearby galaxies using the Spitzer Space Telescope
Authors: Matsuura Mikako
Published: April 2010

Due to their brightness in infrared, asymptotic giant branch (AGB) stars are in important evolutionary stage to be understood at this wavelength. In particular, in next decades, when the infrared optimised telescopes, such as the JWST and the ELT are in operation, it will be essential to include the AGB phase more precisely into the population synthesis models. However, the AGB phase is still one of the remaining major problems in the stellar evolution. This is because the AGB stellar evolution is strongly affected by the mass-loss process from the stars. It is important to describe mass loss more accurately so as to incorporate it into stellar evolutionary models. Recent observations using the Spitzer Space Telescope (SST) enabled us to make a significant progress in understanding the mass loss from AGB stars. Moreover, the SST large surveys contributed to our understanding of the role of AGB stars in chemical enrichment process in galaxies. Here we present the summary of our recent progress.
Metallicity Mapping with gri Photometry: The Virgo Overdensity and the Halos of the Galaxy
Authors: Beers Timothy C. , An Deokkeun , Johnson Jennifer A. , Pinsonneault Marc H. , Terndrup Donald M. , Delahaye Franck , Lee Young Sun , Masseron Thomas , Carollo Daniela , Yanny Brian
Published: April 2010

We describe the methodology required for estimation of photometric estimates of metallicity based on the SDSS gri passbands, which can be used to probe the properties of main-sequence stars beyond ~10 kpc, complementing studies of nearby stars from more metallicity-sensitive color indices that involve the u passband. As a first application of this approach, we determine photometric metal abundance estimates for individual main-sequence stars in the Virgo Overdensity, which covers almost 1000 deg2 on the sky, based on a calibration of the metallicity sensitivity of stellar isochrones in the gri filter passbands using field stars with well-determined spectroscopic metal abundances. Despite the low precision of the method for individual stars, internal errors of σ[Fe/H]~0.1 dex can be achieved for bulk stellar populations. The global metal abundance of the Virgo Overdensity determined in this way is 〈[Fe/H]〉 = −2.0±0.1 (internal) ±0.5 (systematic), from photometric measurements of 0.7 million stars with heliocentric distances from ~10 kpc to ~20 kpc. A preliminary metallicity map, based on results for 2.9 million stars in the northern SDSS DR-7 footprint, exhibits a shift to lower metallicities as one proceeds from the inner- to the outer-halo population, consistent with recent interpretation of the kinematics of local samples of stars with spectroscopically available metallicity estimates and full space motions.
The current status on the UV upturn
Authors: Yi Sukyoung K.
Published: April 2010

The UV upturn phenomenon found in giant elliptical galaxies through space observations has been a mystery. Recent GALEX observations have revealed new facts. The most notable is the rarity of UV upturn galaxies. Unlike previous beliefs, UV upturn is found only in less than 10 percent of giant ellitpical galaxies. Another notable finding is that the UV flux has been increasing for the last couple of billion years. This is consistent with the theoretical predictions that suggest hot horizontal branch stars are the main UV sources. Remaining theoretical and observational issues on this topic can be found in another recent review of mine (Yi 2008).
Dissecting the Formation Histories of Galaxies with Stellar Populations Models
Authors: Labbé Ivo
Published: April 2010

How did galaxies evolve from primordial fluctuations to the well-ordered but diverse population of disk and elliptical galaxies that we observe today? Stellar populations synthesis models have become a crucial tool in addressing this question by helping us to interpret the spectral energy distributions of present-day galaxies and their high redshift progenitors in terms of fundamental characteristics such as stellar mass and age. I will review our current knowledge on the evolution of stellar populations in early- and late type galaxies atz< 1 and the tantalizing – but incomplete – view of the stellar populations in galaxies at 1 <z< 3, during the global peak of star formation. Despite great progress, many fundamental questions remain: what processes trigger episodes of galaxy-scale star formation and what quenches them? To what degree does the star formation history of galaxies depend on the merger history, (halo) mass, or local environment? I will discuss some of the challenges posed in interpreting current data and what improved results might be expected from new observational facilities in the near- and more distant future.
Probing the stellar population of seyfert galaxies: a near infrared perspective
Authors: Riffel Rogério , Pastoriza Miriani G. , Rodríguez-Ardila Alberto , Bonatto Charles
Published: April 2010

We employ IRTF SpeX NIR (0.8–2.4μm) spectra to investigate the stellar population (SP), active galactic nuclei (AGN), featureless continuum (FC) and hot dust properties in 9 Sy 1 and 15 Sy 2 galaxies. Both the starlight code and the hot dust as an additional base element were used for the first time in this spectral range. Our synthesis shows significant differences between Sy 1 and Sy 2 galaxies: the hot dust component is required to fit the K-band spectra of ~90% of the Sy 1 galaxies, and only of ~25% of the Sy 2; about 50% of the Sy 2 galaxies require an FC component contribution ≳20%; this fraction increases to about 60% in the Sy 1. In about 50% of the Sy2, the combined FC and young components contribute with more than 20%, while this occurs in 90% of the Sy1, suggesting recent star formation in the central region. The central few hundred parsecs of our galaxy sample contain a substantial fraction of intermediate-age SPs with a mean metallicity near solar. Our SP synthesis confirms that the 1.1μm CN band can be used as a tracer of intermediate-age stellar populations.
DEEP, AEGIS, & CATS - Pathfinding Surveys to the Next Generation of Distant Galaxy Stellar Population Research
Authors: Koo David C. ,   DEEP2,   AEGIS,   CATS Teams
Published: April 2010

DEEP, AEGIS, and CATS are examples of spectroscopic, multiwavelength, and adaptive optics surveys, respectively, that are pushing the frontiers of stellar population studies of distant galaxies. Together, these surveys affirm the unprecedented richness of high quality information that can already be gathered using today's generation of ground and space telescopes. We highlight several results in extracting the stellar and dynamical masses, chemical abundances, ages, and frequency of galactic winds for galaxies at redshifts up to z ~ 1.4.
What have we learned from large spectroscopic surveys?
Authors: Blanton Michael R.
Published: April 2010

An essential use of stellar population synthesis methods is to interpret the observations of galaxies, to infer their star-formation and assembly histories. I describe here some of the uses of these techniques over the past few years, primarily in the context of local galaxy redshift surveys. For this purpose, such surveys have both advantages and disadvantages relative to higher signal-to-noise but smaller studies, which I discuss. After discussing general issues, I describe how the substantial model uncertainties impact the analysis of galaxy spectra. Then, I discuss the special case of elliptical galaxies, arguing that investigators have made interesting discoveries even in the absence of perfect (or even good) models. I then describe the desiderata for massive higher redshift surveys and the trade-offs that must be made between cosmological and galaxy-focused science, in qualitative terms.
The Promise of Multiwavelength and IFU Observations
Authors: Kennicutt Robert C. , Hao Cai-Na , Johnson Benjamin D. , Rosales-Ortega Fabian , Díaz Angeles , Pasquale Anna , Sánchez Sebastian F.
Published: April 2010

Many of the advances of the last decade in this subject have been the result of large spectroscopic surveys of galaxies on the one hand, and multi-wavelength surveys of galaxies on the other. This talk highlights applications that exploit a combination of spectroscopic and multi-wavelength diagnostics. Most applications to date have been based on spatially integrated measurements of galaxies, but the introduction of wide-field integral field spectrometers promises to extend ths approach to spatially-resolved analyses of galaxies.
Building the red sequence through gas-rich major mergers
Authors: Wild Vivienne , Walcher C. Jakob , Johansson Peter H.
Published: April 2010

Understanding the details of how the red sequence is built is a key question in galaxy evolution. What are the relative roles of gas-rich vs. dry mergers, major vs. minor mergers or galaxy mergers vs. gas accretion? In a recent paper (Wild et al. 2009), we compare hydrodynamic simulations with observations to show how gas-rich major mergers result in galaxies with strong post-starburst spectral features, a population of galaxies easily identified in the real Universe using optical spectra. Using spectra from the VVDS deep survey with  = 0.7, and a principal component analysis technique to provide indices with high enough SNR, we find that 40% of the mass flux onto the red-sequence could enter through a strong post-starburst phase, and thus through gas-rich major mergers. The deeper samples provided by next generation galaxy redshift surveys will allow us to observe the primary physical processes responsible for the shut-down in starformation and build-up of the red sequence.
The Slow Growth of Massive Galaxies in Rapidly Growing Dark Matter Halos
Authors: Brown Michael J. I. ,   the Boötes Field Collaborations
Published: April 2010

In cold dark matter cosmologies, the most massive dark matter halos are predicted to undergo rapid growth at z < 1. While there is the expectation that massive galaxies will also rapidly grow via merging, recent observational studies conclude that the stellar masses of the most massive galaxies grow by just ~ 30% at z < 1. We have used the observed space density and clustering of z < 1 red galaxies in Boötes to determine how these galaxies populate dark matter halos. In the most massive dark matter halos, central galaxy stellar mass is proportional to halo mass to the power of a ~1/3 and much of the stellar mass resides within satellite galaxies. As a consequence, the most massive galaxies grow slowly even though they reside within rapidly growing dark matter halos.
Modeling high-redshift galaxies: what can we learn from high and ultra-high resolution hydrodynamical simulations?
Authors: Devriendt J. , Slyz A. , Powell L. , Pichon C. , Teyssier R.
Published: April 2010

We present results from a high resolution cosmological galaxy formation simulation called Mare Nostrum and a ultra-high resimulation of the first 500 million years of a single, Milky Way (MW) sized galaxy. Using the cosmological run, we measure UV luminosity functions and assess their sensitivity to both cosmological parameters and dust extinction. We find remarkably good agreement with the existing data over the redshift range 4 < z < 7 provided we adopt the favoured cosmology (WMAP 5 year parameters) and a self-consistent treatment of the dust. Cranking up the resolution, we then study in detail a z = 9 protogalaxy sitting at the intersection of cold gas filaments. This high-z MW progenitor grows a dense, rapidly spinning, thin disk which undergoes gravitational fragmention. Star formation in the resulting gas clumps rapidly turns them into globular clusters. A far reaching galactic wind develops, co-powered by the protogalaxy and its cohort of smaller companions populating the filaments. Despite such an impressive blow out, the smooth filamentary material is hardly affected at these redshifts.
Testing star formation rate indicators using galaxy merger simulations and radiative transfer
Authors: Hayward Christopher C. , Jonsson Patrik , Noeske Kai , Wuyts Stijn , Cox T. J. , Narayanan Desika , Groves Brent , Hernquist Lars
Published: April 2010

We discuss our ongoing project analyzing N-body/smoothed-particle hydrodynamics simulations of isolated and merging galaxies, performed using GADGET-2 (Springel 2005), with the 3-D adaptive grid, polychromatic Monte Carlo radiative transfer code SUNRISE (Jonsson 2006). We apply commonly used UV, optical, and IR star formation rate (SFR) indicators to the integrated spectral energy distributions (SEDs) of the simulated galaxies in order to determine how well the SFR indicators recover the instantaneous SFR in the simulations. The models underlying each SFR indicator must necessarily make assumptions about physical properties of the galaxies, e.g., the star formation history (SFH), whereas all such properties are known in the simulations. This enables us to test and compare SFR indicators in a way that is complementary to observational studies. We present one preliminary result of interest: even after correcting the Hα luminosity for dust using the Calzetti et al. (2000) attenuation law the SFR is significantly underestimated for simulated galaxies with SFR ≳ 10 M⊙ yr−1.
The Shining Future of UV Spectral Synthesis
Authors: Pellerin Anne , Finkelstein Steven L.
Published: April 2010

With the coming generation of instruments and telescopes capable of spectroscopy of high redshift galaxies, the spectral synthesis technique in the rest-frame UV and Far-UV range will become one of a few number of tools remaining to study their young stellar populations in detail. The rest-frame UV lines and continuum of high redshift galaxies, observed with visible and infrared telescopes on Earth, can be used for accurate line profile fitting such as Pvλλ1118, 1128, Ciiiλ1176, and Civλ1550. These lines are very precise diagnostic tools to estimate ages, metallicities, and masses of stellar populations.

Here we discuss the potential for spectral synthesis of rest-frame UV spectra obtained at the Keck telescope. As an example, we study the 8 o'clock arc, a lensed galaxy at z=2.7322. We show that the poor spectral type coverage of the actual UV empirical spectral libraries limits the age and metallicity diagnostic. In order to improve our knowledge of high redshift galaxies using spectral synthesis, UV stellar libraries need to be extended to obtain accurate age, metallicity, and mass estimates likely to be occuring in young stellar populations observed in the early universe.
Concluding Remarks: Recent Achievements and Future Challenges in Stellar Population Studies
Authors: Charlot Stephane
Published: April 2010

To conclude this exciting conference on Stellar Populations: Planning for the Next Decade, we have sacrificed the traditional ‘conference summary’ for an opinion poll among all invited speakers on two issues: the most important achievements in the field of stellar populations over the past few years; and the most important challenges for the coming decade. The answers to this poll were remarkably uniform, indicating that the field of stellar populations has a clear future in the era when several new major research facilities are coming online.
Extragalactic GCs in the near-infrared: genuinely old in E/S0's?
Authors: Chies-Santos Ana L. , Larsen Søren S.
Published: April 2010

Globular cluster (GC) systems are powerful probes to study the evolutionary histories of galaxies, being tracers of major star fomation episodes (Brodie & Strader 2006). They are found around all major galaxies and are easy to see far beyond the local group. Age dating GCs therefore helps pinpoint epochs of major star forming events. Spectroscopic age dating though (Strader et al. 2005) is extremely time consuming and can only access the few brightest clusters. An alternative is to combine near-infrared (NIR) and optical photometry, and therefore have a better chance in lifting the age metallicity degeneracy than with optical colours alone. This approach relies in testing GC colours against simple stellar population (SSP) models. The first studies following this technique showed the possible existence of a high percentage of intermediate age (2-3 Gyrs) GCs in early-type galaxies known to contain old stellar populations from integrated light studies. Two strong cases can be listed: NGC 4365 (Puzia et al. 2002, Larsen et al. 2005) and NGC 5846 (Hempel et al. 2003). In the present study we combine NIR deep photometry obtained with the WHT/LIRIS instrument and archival HST/ACS optical images to determine g(F475W), z(F840LP) and K(2.2m) magnitudes and colours of GCs in 14 early-type galaxies.
The Effects of Galactic Winds on the Chemical Evolution of Baryons
Authors: De Rossi María E. , Tissera Patricia B.
Published: April 2010

During the last decade, the development of more sophisticated surveys allows the exploration of the chemical enrichment of galaxies and their environment at different cosmic times. In this context, it has been suggested that galactic winds play a fundamental role in the regulation of the star formation and the transportation of metals outside the galaxies. In this work, we study the influence of Supernovae winds in the chemical evolution of galaxies and the intergalactic medium by employing cosmological numerical simulations within a hierarchical Universe. We focus on the origin and evolution of the mass-metallicity relation (MZR).
The Tully-Fisher Relation in Numerical Simulations of Structure Formation
Authors: De Rossi María E. , Tissera Patricia B. , Pedrosa Susana E.
Published: April 2010

The Tully-Fisher Relation (TFR) is of fundamental importance for galaxy formation as it provides information about the relation between the baryonic content of galaxies and the depth of their dark halos potential wells. In recent years, it has been possible to study this relation at different redshifts. However, there are still controversies about its origin and evolution. In this work, we try to address the origin of the Tully-Fisher Relation by employing cosmological hydrodynamical simulations.
A near-infrared view of AGB stars in nearby dwarf galaxies
Authors: Gullieuszik M. , Held E. V. , Girardi L. , Rizzi L. , Marigo P. , Saviane I. , Momany Y.
Published: April 2010

As part of our near-infrared photometric survey of nearby dwarf galaxies, we present recent results for Leo I and Leo II dwarf spheroidal galaxies. We selected O- and C-rich AGB stellar populations using two-color diagrams and compared their luminosity functions and star counts with the predictions of the most recent AGB theoretical models.
Mid-UV Spectral Diagnostics
Authors: Heap Sara R. , Lindler Don
Published: April 2010

The mid-ultraviolet is an important diagnostic region due to its sensitivity to the hottest stars of a stellar population. Sources of mid-UV flux include main sequence turn-off stars, the basic clocks of stellar evolution, and also blue horizontal branch stars and blue stragglers. We describe some observed trends in mid-UV colors and spectral indices.
The star formation history of the Fornax dwarf spheroidal galaxy
Authors: Held Enrico V. , Tolstoy Eline , Rizzi Luca , Cesetti Mary , Cole Andrew A. , Battaglia Giuseppina , Da Costa Gary S. , Gullieuszik Marco , Mateo Mario , Olszewski Edward W. , Walker Matthew G.
Published: April 2010

We present the first results of a comprehensive HST study of the star-formation history of Fornax dSph, based on WFPC2 imaging of 7 Fornax fields. Our observations reach the oldest main-sequence turnoffs, allowing us to address fundamental questions of dwarf galaxy evolution, such as the spatial variations in the stellar content, and whether the old stellar population is made up of stars formed in a very early burst or the result of a more continuous star formation.
On the parameterization of single and binary stars
Authors: Malkov O. , Sichevskij S. , Kovaleva D. , Myakutin V.
Published: April 2010

Many astrophysical problems in the theory of formation and evolution of stars and stellar groups require knowledge of the mass or age of individual stars. Stellar masses and ages are not directly observable parameters, and most of the methods used to determine them are based on the calibrating relations obtained from observations or from theoretical considerations. In most cases, the mass-luminosity relation, based on the masses of approximately two hundred well-studied binaries, is the only way to estimate the mass of single stars. Unfortunately, the statistical nature of the mass-luminosity relation means that the stellar masses determined with it may only be considered as approximate. The establishment of methods for estimating stellar masses and ages of stars with accuracy comparable to direct methods remains a challenging task. This work proposes a way to use the location of a star in the HR diagram to estimate its mass and age based on modern stellar models. The method is based on the geometric similarity of evolutionary tracks for the stars at the same evolutionary stage. To examine the proposed approach and involved assumptions, it has been applied to various test data sets.
Spiral triggering of star formation in normal galaxies
Authors: Martínez-García Eric E. , González-Lópezlira Rosa Amelia , Bruzual-A. Gustavo
Published: April 2010

We present results for 13 spiral galaxies from a sample of 31, where we have used the method developed by González & Graham 1996, to search for and analyze azimuthal color gradients across spiral arms (see figure 1 in Martínez-García et al. 2009). A total of 23 regions were analyzed in the spiral disks. Ten of the galaxies present regions that match theoretical predictions.
The nature of the LINER in the galaxy NGC 404
Authors: Menezes Roberto B. , Steiner João E. , Ricci Tiago V. , Oliveira Alexandre S.
Published: April 2010

NGC 404, at a distance of 3.4 Mpc, is the nearest S0 galaxy. This galaxy harbors a LINER; however, since the spectrum does not show a broad Hα emission, it is not certain that this LINER is a low luminosity AGN and its nature is still an open question. HST observations show the existence of stellar populations with an age of 3 × 108 years in the galactic bulge and with an age of 6–15 × 109 years in the galactic disk. In this work, we present an analysis of the data cube of NGC 404 obtained with the IFU (Integral Field Unity) of the GMOS (Gemini Multi-Object Spectrograph) on the Gemini North telescope.
Stellar populations of disc galaxies: from the center of the bulge to the edge of the disc
Authors: Morelli L. , Pompei E. , Pizzella A. , Coccato L. , Corsini E. M. , Mendez Abreu J. , Saglia R. , Sarzi M. , Bertola F.
Published: April 2010

We present extensive photometric and spectroscopic study to give a new insight in the bulge stellar population. Super-solar α/Fe and its constant value along the radial profile, in most of the galaxies, suggest that the star formation in these objects has been fast and occurred at the same time in the whole bulge.
Young Stellar Populations in the Collisional Ring Galaxy NGC 922
Authors: Pellerin A. , Meurer G. R. , Bekki K. , Elmegreen D. M. , Wong O. I. , Knezek P.
Published: April 2010

We studied the star cluster population properties in the nearby collisional ring galaxy NGC 922 using HST/WFPC2 photometry and population synthesis modeling. We found that 69% of the detected clusters are younger than 7 Myr, and that most of them are located in the ring or along the bar, consistent with the strong Hα emission. The images also show a tidal plume pointing toward the companion. Its stellar age is consistent with pre-existing stars that were probably stripped off during the passage of the companion. We compared the star-forming complexes observed in NGC 922 with those of a distant ring galaxy from the GOODS eld. It indicates very similar masses and sizes, suggesting similar origins. Finally, we found clusters that are excellent progenitor candidates for faint fuzzy clusters.
Control sample for galaxy pairs: Simulations and Observations
Authors: Perez Josefa , Tissera Patricia
Published: April 2010

Several attempts have been made in order to isolate the effect of galaxy interactions by comparing galaxy in pairs with isolated galaxies. However, different authors have proposed different ways to build these control samples (CS). By using mock galaxy catalagues built up from the Millennium Simulation, we show that the set of constrains used to define a CS might introduce biases which could affect the interpretation of results. In this analysis, we make use of the fact that the physics of interactions is not included in the semi-analytic model, so that any difference between the mock control and pair samples can be attributed to selection biases. Thus, we suggest how to build an unique and unbiased CS in order to individualize the effect of interactions. Based on this theoretical findings and using the SDSS-DR4 data, we revise some previous observational results of galaxy in pairs in order to evaluate any possible disagreement. The comparison between simulations and observations suggests an overestimated effect of the DM halo bias in semianalytical models.
Abundance Patterns Among Very Metal-Poor Stars in the Halo of the Galaxy: A Statistical Approach
Authors: Placco Vinicius M. , Rossi Silvia , Beers Timothy C. , Lucatello Sara
Published: April 2010

The main goal of this work is to explore the abundance patterns of the very metal-poor stars ([Fe/H]<−2.0) observed by the HERES (Hamburg ESO R-process Enhanced Star - Christlieb et al. 2004) survey. This type of study allows the analysis of the correlations among chemical elements, and place some constraints on the operation of the neutron-capture (r and s) processes in the early Galaxy. This approach makes use of statistical tools, such as agglomerative nesting, which can identify the formation of natural groups based on relations among elemental abundances (e.g. [C/Fe], [Sr/Fe], [Ba/Fe], and [Eu/Fe]), and can also be used in a series of “large-sample like” studies.

This study provides a comprehensive analysis of a sample of 326 metal-poor stars, and introduces two new subclasses (r-0 and s-I) for metal-poor stars with determined abundances of neutron-capture elements, aiming to standardize the nomenclature for those objects and, by reproducing previous results, confirms the validity of the statistical method used.
Stellar populations in Luminous Red Galaxies: cosmic chronometers?
Authors: Ratsimbazafy A. L. , Cress C. M. , Blyth S. L. , Crawford S. M. , Olivier E. A. , van der Heyden K. J.
Published: April 2010

The expansion rate of the Universe can potentially be measured using age-dating of Luminous Red Galaxies (LRGs). Here, we explore the validity of the assumptions implicit in this method using LRGs identified in the Millenium Simulation (MS). We use stellar population modelling and spectral synthesis to estimate the errors on ages that can be expected and discuss optimization of such an experiment. We find that H(z) using simulated galaxies from MS can be recovered with high accuracy. Using single stellar populations (SSPs) to age-date LRGs is not sufficient but if the MS star formation histories of galaxies are used, accurate ages are obtainable. We discuss an observing program to carry out this experiment using SALT (Southern African Large Telescope).
Stellar Populations in Barred Galaxies
Authors: Robert C. , Cantin S. , Mollá M. , Pellerin A. , Brière É.
Published: April 2010

We developed an iterative technique to better characterize stellar populations and the central activity of barred galaxies using evolutionary synthesis codes and OASIS data. The case of NGC 5430 is presented here. Our results are reinforcing the role played by the bar and nuclear structures for the evolution of galaxies.
Morphological transformation of NGC 205?
Authors: Saviane Ivo , Monaco Lorenzo , Hallas Tony
Published: April 2010

NGC 205 is a small galaxy (M/M⊙ = 0.7 × 109; MV = −16.6) currently located 36′ NW of M31. It is classified as dE because in ground-based images it appears as an elliptical body. However past investigations have revealed characteristics that are more typical of a disk galaxy: the specific frequency of globular clusters is 1.8; the large scale dynamics shows partial rotational support; there is a significant amount (106M⊙) of rotating gas (molecular and atomic) and dust; the central regions harbor a fairly complex stellar population, including a 100–500 Myr old nucleus surrounded by 50- and 100-Myr old stellar associations (see references in Monaco et al. 2009; M09). Very recently, thanks to hst/acs imaging we have been able to reveal a young central ‘field’ population (M09), extending out to ~40″ in radius (~160 pc). The luminosity function of the main sequence can be fitted with Saviane et al. (2004) model of continuous star formation (SF) from at least ~600 Myr ago to ~60 Myr ago. We found that 1.5 × 105M⊙ in stars were produced from ~300 Myr to ~60 Myr ago, with a SF rate of 7 × 10−4M⊙ yr−1. A continuous SF seems to support the latest simulations of NGC 205 orbit: Howley et al. (2008) found that the galaxy must be moving with a velocity 300–500 km s−1 (comparable to the escape velocity) along an almost radial orbit, and it should be approaching M31 for the first time. An episodic SF triggered by passages through M31 disk every ~300 Myr in a bound orbit (Cepa & Beckman 1988) is excluded by our data.
The Apache Point Observatory Galactic Evolution Experiment (APOGEE)
Authors: Schiavon Ricardo P. , Majewski Steven R.
Published: April 2010

The Apache Point Observatory Galactic Evolution Experiment (APOGEE) is a large scale, high-resolution, near-infrared spectroscopic survey of Milky Way stellar populations and one of the four experiments in the Sloan Digital Sky Survey III (SDSS-III). APOGEE will be based on a new multi-fiber cryogenic spectrograph, currently under construction, expected to begin survey observations on the 2.5 m Sloan telescope in the Spring of 2011. APOGEE will measure high-precision radial velocities and elemental abundances for ~15 elements for ~ 105 stars, and is expected to shed new light on the processes that led to the formation of the Galaxy.
Star-forming regions in the intragroup medium of compact groups of galaxies
Authors: Torres-Flores S. , Mendes de Oliveira C. , de Mello D. F. , Amram P. , Plana H. , Epinat B. , Iglesias-Páramo J.
Published: April 2010

We present the results of a multiwavelength campaign searching for young objects in the intragroup medium of seven compact groups of galaxies: HCG 2, 7, 22, 23, 92, 100 and NGC 92. We used Fabry-Perot velocity fields and rotation curves together with GALEX NUV and FUV images, optical R-band and HI maps to evaluate the stage of interaction of each group. We conclude that groups (i) HCG 7 and HCG 23 are in an early stage of interaction, (ii) HCG 2 and HCG 22 are mildly interacting, and (iii) HCG 92, HCG 100 and NGC 92 are in a late stage of evolution. Evolved groups have a population of young objects in their intragroup medium while no such population is found within the less evolved groups. We also report the discovery of a tidal dwarf galaxy candidate in the tail of NGC 92. These three groups, besides containing galaxies which have peculiar velocity fields, also show extended HI tails. Our results indicate that the advanced stage of evolution of a group together with the presence of intragroup HI clouds may lead to star formation in the intragroup medium.
Stellar formation in Brightest Cluster Galaxies
Authors: Zapata Pichinao Tatiana , Lima Neto Gastão B.
Published: April 2010

We study the interplay between stellar population of the Brightest Cluster Galaxies (BCG) and cluster global properties. We use X-ray properties from Chandra, ROSAT and ASCA observations and BCGs spectra from SDSS-DR6. Using STARLIGHT we determined the star formation history of the BCGs and look for relations with the intra-cluster gas properties. Our first results show no correlation between the recent star formation with x-ray temperature and dynamic state. An important star formation is happening in cool-core Cluster. This new stellar population has low metallicity, pointing to an external source of cold gas to form stars.