Structures in surface-brightness profiles of LMC and SMC star clusters: evidence of mergers?

The LMC and SMC are rich in binary star clusters, and some mergers are expected. It is important to characterize single clusters, binary clusters and candidates to mergers. We selected a sample of star clusters in each Cloud with this aim. Surface photometry of 25 SMC and 22 LMC star clusters was carried with the ESO Danish 1.54 m telescope. 23 clusters were observed for the first time for these purposes. We fitted Elson, Fall and Freeman (1987, EFF) profiles to the data, deriving structural parameters, luminosities and masses. We also use isophotal maps to constrain candidates to cluster interactions.} {The structural parameters, luminosities and masses presented good agreement with those in the literature. Three binary clusters in the sample have a double profile. Four clusters (NGC 376, K 50, K 54 and NGC 1810) do not have companions and present as well important deviations from EFF profiles. The present sample contains blue and red Magellanic clusters. Extended EFF profiles were detected in some blue clusters. We find evidence that important deviations from the body of EFF profiles might be used as a tool to detect cluster mergers.Comment: 16 pages and 8 figures. Accepted by A&

Newly Identified Star Clusters in M33. III. Structural Parameters

We present the morphological properties of 161 star clusters in M33 using the Advanced Camera For Surveys Wide Field Channel onboard the Hubble Space Telescope using observations with the F606W and F814W filters. We obtain, for the first time, ellipticities, position angles, and surface brightness profiles for a significant number of clusters. On average, M33 clusters are more flattened than those of the Milky Way and M31, and more similar to clusters in the Small Magellanic Cloud. The ellipticities do not show any correlation with age or mass, suggesting that rotation is not the main cause of elongation in the M33 clusters. The position angles of the clusters show a bimodality with a strong peak perpendicular to the position angle of the galaxy major axis. These results support the notion that tidal forces are the reason for the cluster flattening. We fit King and EFF models to the surface brightness profiles and derive structural parameters including core radii, concentration, half-light radii and central surface brightness for both filters. The surface brightness profiles of a significant number of clusters show irregularities such as bumps and dips. Young clusters (Log age < 8) are notably better fitted by models with no radial truncation (EFF models), while older clusters show no significant differences between King or EFF fits. M33 star clusters seem to have smaller sizes, smaller concentrations, and smaller central surface brightness as compared to clusters in the MW, M31, LMC and SMC. Analysis of the structural parameters presents a age-radius relation also detected in other star cluster systems. The overall analysis shows differences in the structural evolution between the M33 cluster system and cluster systems in nearby galaxies. These differences could have been caused by the strong differences in these various environments.Comment: 30 pages, 12 figures, accepted for publication in MNRA

Young Clusters in the Magellanic Clouds II

We present the results of a quantitative study of the degree of extension to the boundary of the classical convective core within intermediate mass stars. The basis of our empirical study is the stellar population of four young populous clusters in the Magellanic Clouds which has been detailed in Keller, Bessell & Da Costa (2000). The sample affords a meaningful comparison with theoretical scenarios with varying degrees of convective core overshoot and binary star fraction. Two critical properties of the population, the main-sequence luminosity function and the number of evolved stars, form the basis of our comparison between the observed data set and that simulated from the stellar evolutionary models. On the basis of this comparison we conclude that the case of no convective core overshoot is excluded at a 2 sigma level.Comment: 27 pages, 12 figures, AJ accepte

The Extended Main-Sequence Turn-off Clusters of the Large Magellanic Cloud - Missing links in Globular Cluster Evolution

Recent observations of intermediate age (1 - 3 Gyr) massive star clusters in the Large Magellanic Cloud (LMC) have revealed that the majority possess bifurcated or extended main-sequence turn-off (EMSTO) morphologies. This effect can be understood to arise from subsequent star formation amongst the stellar population with age differences between constituent stars amounting to 50 - 300 Myr. Age spreads of this order are similarly invoked to explain the light element abundance variations witnessed in ancient globular clusters. In this paper we explore the proposition that the clusters exhibiting the EMSTO phenomenon are a general phase in the evolution of massive clusters, one that naturally leads to the particular chemical properties of the ancient globular cluster population. We show that the isolation of EMSTO clusters to intermediate ages is the consequence of observational selection effects. In our proposed scenario, the EMSTO phenomenon is identical to that which establishes the light element abundance variations that are ubiquitous in the ancient globular cluster population. Our scenario makes a strong prediction: EMSTO clusters will exhibit abundance variations in the light elements characteristic of the ancient GC population.Comment: ApJ accepted. 33 pages, 5 figure

Mass segregation in young compact star clusters in the Large Magellanic Cloud: I. Data and Luminosity Functions

We have undertaken a detailed analysis of HST/WFPC2 and STIS imaging observations, and of supplementary wide-field ground-based observations obtained with the NTT of two young ~10-25 Myr) compact star clusters in the LMC, NGC 1805 and NGC 1818. The ultimate goal of our work is to improve our understanding of the degree of primordial mass segregation in star clusters. This is crucial for the interpretation of observational luminosity functions (LFs) in terms of the initial mass function (IMF), and for constraining the universality of the IMF. We present evidence for strong luminosity segregation in both clusters. The LF slopes steepen with cluster radius; in both NGC 1805 and NGC 1818 the LF slopes reach a stable level well beyond the clusters' core or half-light radii. In addition, the brightest cluster stars are strongly concentrated within the inner ~4 R_hl. The global cluster LF, although strongly nonlinear, is fairly well approximated by the core or half-light LF; the (annular) LFs at these radii are dominated by the segregated high-luminosity stars, however. We present tentative evidence for the presence of an excess number of bright stars surrounding NGC 1818, for which we argue that they are most likely massive stars that have been collisionally ejected from the cluster core. We therefore suggest that the cores of massive young stars clusters undergo significant dynamical evolution, even on time-scales as short as ~25 Myr.Comment: 19 pages, incl. 10 embedded postscript figures, MNRAS, resubmitted (referee's comments included

A joint experimental and theoretical study on the electronic structure and photoluminescence properties of Al2(WO4)3 powders

In this paper, aluminum tungstate Al2(WO4)3 powders were synthesized using the co-precipitation method at room temperature and then submitted to heat treatment processes at different temperatures (100, 200, 400, 800, and 1000 °C) for 2 h. The structure and morphology of the powders were characterized by means of X-ray diffraction (XRD), Rietveld refinement data, and field emission scanning electron microscopy (FE-SEM) images. Their optical properties were examined with ultraviolet-visible (UV-vis) diffuse reflectance spectroscopy and photoluminescence (PL) measurements. XRD patterns and Rietveld refinement data showed that Al2(WO4)3 powders heat treated at 1000 °C for 2 h have a orthorhombic structure with a space group (Pnca) without the presence of deleterious phases. FE-SEM images revealed that these powders are formed by the aggregation of several nanoparticles leading to the growth of microparticles with irregular morphologies and an agglomerated nature. UV-vis spectra indicated that optical band gap energy increased from 3.16 to 3.48 eV) as the processing temperature rose, which was in turn associated with a reduction in intermediary energy levels. First-principle calculations were performed in order to understand the behavior of the PL properties using density functional theory at the B3LYP calculation level on periodic model systems and indicate the presence of stable electronic excited states (singlet). The analyses of the band structures and density of states at both ground and first excited electronic states provide insight into the main features, based on structural and electronic order-disorder effects in octahedral [AlO6] clusters and tetrahedral [WO4] clusters, as constituent building units of this material

The Hubble Constant from Observations of the Brightest Red Giant Stars in a Virgo-Cluster Galaxy

The Virgo and Fornax clusters of galaxies play central roles in determining the Hubble constant H_0. A powerful and direct way of establishing distances for elliptical galaxies is to use the luminosities of the brightest red-giant stars (the TRGB luminosity, at M_I = -4.2). Here we report the direct observation of the TRGB stars in a dwarf elliptical galaxy in the Virgo cluster. We find its distance to be 15.7 +- 1.5 Megaparsecs, from which we estimate a Hubble constant of H_0 = 77 +- 8 km/s/Mpc. Under the assumption of a low-density Universe with the simplest cosmology, the age of the Universe is no more than 12-13 billion years.Comment: 12 pages, LaTeX, with 2 postscript figures; in press for Nature, July 199

Pharmacognostic characterization of Celtis iguanaea (Jacq.) Sargent

Celtis iguanaea (Jacq.) Sargent (Ulmaceae) é conhecida popularmente como esporão-de-galo e amplamente utilizada na medicina popular brasileira. O objetivo desse trabalho foi realizar o estudo farmacognóstico das folhas e caules jovens da C. iguanaea através de análises macro e microscópicas, triagem fitoquímica, ensaios de pureza (umidade, cinzas totais e insolúveis em ácido) e determinação dos teores de polifenóis e flavonóides totais. As folhas são anfiestomáticas, apresentando grande quantidade de tricomas tectores, litocistos e estômatos na epiderme abaxial. Na triagem fitoquímica foram detectados mucilagem, flavonóides e cumarinas. Os teores de umidade, cinzas totais, cinzas insolúveis em ácido, polifenóis e flavonóides totais encontrados, foram de 7,05 ± 0,22 %, 18,2 ± 0,18 %, 7,43 ± 1,03 %, 0,55 ± 0,03 % e 0,53 ± 0,007 %, respectivamente. Esses resultados podem subsidiar estudos futuros e contribuir para a obtenção de informações relevantes acerca da padronização e controle de qualidade da matéria-prima dessa espécie.Celtis iguanaea (Jacq.) Sargent (Ulmaceae) is popularly known as esporão-de-galo and widely used in Brazilian folk medicine. The aim of this work was to perform a pharmacognostic study of C. iguanaea leaves and young stem through macro and microscopic analysis as well as phytochemical screening, purity assays (moisture, total and acid insoluble ash contents), total polyphenols and total flavonoids contents. The leaves are amphistomatic, presenting large amounts of tector trichomes, lytocists and stomata were noted on the abaxial leaf surface epidermis. The phytochemical screening detected flavonoids, coumarins and mucilage. The moisture, total ash, acid insoluble ash, polyphenol and flavonoid contents were 7.05 ± 0.22 %, 18.2 ± 0.18 %, 7.43 ± 1.03 %, 0.55 ± 0.03 % and 0.53 ± 0.007 %, respectively. These results must to subsidize further studies and contribute to the obtainment of relevant informations about this raw material standardization and quality controlColegio de Farmacéuticos de la Provincia de Buenos Aire

Pharmacognostic characterization of Celtis iguanaea (Jacq.) Sargent

Celtis iguanaea (Jacq.) Sargent (Ulmaceae) é conhecida popularmente como esporão-de-galo e amplamente utilizada na medicina popular brasileira. O objetivo desse trabalho foi realizar o estudo farmacognóstico das folhas e caules jovens da C. iguanaea através de análises macro e microscópicas, triagem fitoquímica, ensaios de pureza (umidade, cinzas totais e insolúveis em ácido) e determinação dos teores de polifenóis e flavonóides totais. As folhas são anfiestomáticas, apresentando grande quantidade de tricomas tectores, litocistos e estômatos na epiderme abaxial. Na triagem fitoquímica foram detectados mucilagem, flavonóides e cumarinas. Os teores de umidade, cinzas totais, cinzas insolúveis em ácido, polifenóis e flavonóides totais encontrados, foram de 7,05 ± 0,22 %, 18,2 ± 0,18 %, 7,43 ± 1,03 %, 0,55 ± 0,03 % e 0,53 ± 0,007 %, respectivamente. Esses resultados podem subsidiar estudos futuros e contribuir para a obtenção de informações relevantes acerca da padronização e controle de qualidade da matéria-prima dessa espécie.Celtis iguanaea (Jacq.) Sargent (Ulmaceae) is popularly known as esporão-de-galo and widely used in Brazilian folk medicine. The aim of this work was to perform a pharmacognostic study of C. iguanaea leaves and young stem through macro and microscopic analysis as well as phytochemical screening, purity assays (moisture, total and acid insoluble ash contents), total polyphenols and total flavonoids contents. The leaves are amphistomatic, presenting large amounts of tector trichomes, lytocists and stomata were noted on the abaxial leaf surface epidermis. The phytochemical screening detected flavonoids, coumarins and mucilage. The moisture, total ash, acid insoluble ash, polyphenol and flavonoid contents were 7.05 ± 0.22 %, 18.2 ± 0.18 %, 7.43 ± 1.03 %, 0.55 ± 0.03 % and 0.53 ± 0.007 %, respectively. These results must to subsidize further studies and contribute to the obtainment of relevant informations about this raw material standardization and quality controlColegio de Farmacéuticos de la Provincia de Buenos Aire

Pharmacognostic characterization of Celtis iguanaea (Jacq.) Sargent

Celtis iguanaea (Jacq.) Sargent (Ulmaceae) é conhecida popularmente como esporão-de-galo e amplamente utilizada na medicina popular brasileira. O objetivo desse trabalho foi realizar o estudo farmacognóstico das folhas e caules jovens da C. iguanaea através de análises macro e microscópicas, triagem fitoquímica, ensaios de pureza (umidade, cinzas totais e insolúveis em ácido) e determinação dos teores de polifenóis e flavonóides totais. As folhas são anfiestomáticas, apresentando grande quantidade de tricomas tectores, litocistos e estômatos na epiderme abaxial. Na triagem fitoquímica foram detectados mucilagem, flavonóides e cumarinas. Os teores de umidade, cinzas totais, cinzas insolúveis em ácido, polifenóis e flavonóides totais encontrados, foram de 7,05 ± 0,22 %, 18,2 ± 0,18 %, 7,43 ± 1,03 %, 0,55 ± 0,03 % e 0,53 ± 0,007 %, respectivamente. Esses resultados podem subsidiar estudos futuros e contribuir para a obtenção de informações relevantes acerca da padronização e controle de qualidade da matéria-prima dessa espécie.Celtis iguanaea (Jacq.) Sargent (Ulmaceae) is popularly known as esporão-de-galo and widely used in Brazilian folk medicine. The aim of this work was to perform a pharmacognostic study of C. iguanaea leaves and young stem through macro and microscopic analysis as well as phytochemical screening, purity assays (moisture, total and acid insoluble ash contents), total polyphenols and total flavonoids contents. The leaves are amphistomatic, presenting large amounts of tector trichomes, lytocists and stomata were noted on the abaxial leaf surface epidermis. The phytochemical screening detected flavonoids, coumarins and mucilage. The moisture, total ash, acid insoluble ash, polyphenol and flavonoid contents were 7.05 ± 0.22 %, 18.2 ± 0.18 %, 7.43 ± 1.03 %, 0.55 ± 0.03 % and 0.53 ± 0.007 %, respectively. These results must to subsidize further studies and contribute to the obtainment of relevant informations about this raw material standardization and quality controlColegio de Farmacéuticos de la Provincia de Buenos Aire