Integrated properties of mass segregated star clusters

In this contribution we study integrated properties of dynamically segregated star clusters. The observed core radii of segregated clusters can be 50% smaller than the ``true'' core radius. In addition, the measured radius in the red filters is smaller than those measured in blue filters. However, these difference are small ($\lesssim10$), making it observationally challenging to detect mass segregation in extra-galactic clusters based on such a comparison. Our results follow naturally from the fact that in nearly all filters most of the light comes from the most massive stars. Therefore, the observed surface brightness profile is dominated by stars of similar mass, which are centrally concentrated and have a similar spatial distribution.Comment: 2 pages, 2 figures. To appear in proceedings of the 246th IAU symposium on "Dynamical evolution of dense stellar systems"; acknowledgements include

On the Estimation of Systematic Uncertainties of Star Formation Histories

In most star formation history (SFH) measurements, the reported uncertainties are those due to effects whose sizes can be readily measured: Poisson noise, adopted distance and extinction, and binning choices in the solution itself. However, the largest source of error, systematics in the adopted isochrones, is usually ignored and very rarely explicitly incorporated into the uncertainties. I propose a process by which estimates of the uncertainties due to evolutionary models can be incorporated into the SFH uncertainties. This process relies on application of shifts in temperature and luminosity, the sizes of which must be calibrated for the data being analyzed. While there are inherent limitations, the ability to estimate the effect of systematic errors and include them in the overall uncertainty is significant. Effects of this are most notable in the case of shallow photometry, with which SFH measurements rely on evolved stars.Comment: 28 pages, 9 figures, ApJ in pres

Stellar populations in the Galactic bulge

AIMS:The aim of this paper is to study the characteristics of the stellar populations and the metallicity distribution in the Galactic bulge. We study the entire stellar population, but also retrieve information using only the red clump stars. METHODS: To study the characteristics of the stellar populations and the metallicity distribution in the Galactic bulge, we compared the output of the galaxy model TRILEGAL, which implements the Binney et al. (1997) bulge model, with observations from 2MASS and OGLE-II. A minimisation procedure has been set up to retrieve the best fitting model with different stellar populations and metallicity distributions. RESULTS: Using the TRILEGAL code we find that the best model resembling the characteristics of the Galactic bulge is a model with the distance to the Galactic centre $R_0 = 8.7\pm^{0.57}_{0.43}$ kpc, the major axis ratios of the bar $1:\eta:\zeta = 1 : 0.68\pm_{0.19}^{0.05} : 0.31\pm_{0.04}^{0.06}$, and the angle between the Sun-centre line and the bar $\phi = 15\deg\pm_{12.7}^{13.3}$. Using these parameters the best model is found for a burst of 8 Gyr, although it is almost indistinguishable from models with ages of 9 and 10 Gyr. The metallicity distribution found is consistent with metallicity distributions in the literature based on spectroscopic results.Comment: A&A accepte

Galaxies in group and field environments: a comparison of optical-NIR luminosities and colors

We compare properties of galaxies in loose groups with those in field environment by analyzing the Nearby Optical Galaxy (NOG) catalog of galaxy systems. We consider as group galaxies, objects belonging to systems with at least five members identified by means of the "friends of friends method", and, as field galaxies, all galaxies with no companions. We analyze both a magnitude--limited sample of 959 and 2035 galaxies (groups vs. field galaxies, respectively, B<14 mag, and 2000<cz<6000 km/s) and a volume-limited sample (M_B <-19.01 mag, 2000<cz<4000 km/s 369 group and 548 field galaxies). For all these galaxies, blue corrected magnitudes and morphological types are available. The cross-correlation of NOG with the 2MASS second release allow us to assign K magnitudes and obtain B-K colors for about half of the galaxies in our samples. We analyze luminosity and color segregation-effects in relation with the morphological segregation. For both B and K bands, we find that group galaxies are, on average, more luminous than field galaxies and this effect is not entirely a consequence of the morphological segregation. After taking into account the morphological segregation, the luminosity difference between group and field galaxies is about 10%. When considering only very early-type galaxies (T<-2) the difference is larger than 30%. We also find that group galaxies are redder than field galaxies, Delta(B-K) about 0.4 mag. However, after taking into account the morphological segregation, we find a smaller B-K difference, poorly significant (only at the c.l. of about 80%).Comment: 11 pages, 10 eps figures, A&A in pres

Clump stars in the Solar Neighbourhood

Hipparcos data has allowed the identification of a large number of clump stars in the Solar Neighbourhood. We discuss our present knowledge about their distributions of masses, ages, colours, magnitudes, and metallicities. We point out that the age distribution of clump stars is ``biased'' towards intermediate-ages. Therefore, the metallicity information they contain is different from that provided by the local G dwarfs. Since accurate abundance determinations are about to become available, these may provide useful constraints to chemical evolution models of the local disc.Comment: 6 pages, proc. of the Sept. 20-24, 1999 Vulcano Workshop "The chemical evolution of the Milky Way: stars vs. clusters", eds. F. Matteucci, F. Giovanell

Extended star formation history of the star cluster NGC 2154 in the Large Magellanic Cloud

The colour-magnitude diagram (CMD) of the intermediate-age Large Magellanic Cloud star cluster NGC 2154 and its adjacent field has been analysed using Padova stellar models to determine the cluster´s fundamental parameters and its star formation history. Deep BR CCD photometry, together with synthetic CMDs and integrated luminosity functions, has allowed us to infer that the cluster experienced an extended star formation period of about 1.2 Gyr, which began approximately 2.3 Gyr ago and ended 1.1 Gyr ago. However, the physical reality of such a prolonged period of star formation is questionable, and could be the result of inadequacies in the stellar evolutionary tracks themselves. A substantial fraction of binaries (70 per cent) seems to exist in NGC 2154.Fil: Baume, Gustavo Luis. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Astrofísica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas. Instituto de Astrofísica La Plata; ArgentinaFil: Carraro, Giovanni. Università di Padova; ItaliaFil: Costa, E.. Universidad de Chile; ChileFil: Mendez, R. A.. Universidad de Chile; ChileFil: Girardi, L.. Osservatorio Astronomico di Padova; Itali

Proposições horticulturais à citricultura para a mitigação de efeitos do huanglongbing (HLB ou greening).

A citricultura é uma das principais atividades do agronegócio brasileiro, está presente em todas as regiões do país em diferentes ambientes de produção e é explorada por todos os tipos de produtores, muitos de base familiar. A presença da doença greening, constatada no Brasil em 2004, vem provocado perdas expressivas em importantes regiões produtoras e coloca em cheque a sustentabilidade da cadeia citrícola. Estratégias de controle atual se baseiam no uso de mudas sadias, inspeção e erradicação sistemática de plantas sintomáticas e controle químico do inseto vetor. Pesquisas vêm sendo conduzidas pela Embrapa e outras instituições brasileiras com o objetivo de alcançar a resistência ao HLB por melhoramento genético via biotecnologia. Mas, as limitações inerentes a essas ações determinam que proposições adicionais sejam consideradas para a mitigação de efeitos do HLB. Práticas horticulturais com possibilidade de emprego imediato na citricultura são apresentadas de forma a contribuir com o enfrentamento a essa doença. As proposições a seguir são discutidas: seleção de materiais tolerantes de ocorrência natural, mudança geográfica da produção, conceitos não usuais de mudas protegidas, plantas repelentes e atrativas, sistemas de produção de baixo ingresso, uso de elicitores de resistência, cultivo protegido, consorciação e mega-adensamento. A adoção das diferentes estratégias em combinação pode permitir a sustentabilidade da atividade até que sejam obtidas cultivares resistentes.Disponível em: Acesso em: 21 fev. 2011

Use of horticultural practices in citriculture to survive Huanglongbing.

Huanglongbing (HLB) was first reported in Brazil in 2004 and had caused severe losses in the main producing regions, threatening the sustainability of the whole citrus chain. Current control strategies are based on the use of healthy nursery trees, inspection and systematic eradication of symptomatic plants, and chemical control of the insect vector