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Coelho P.R.T.,University of Sao Paulo | Coelho P.R.T.,Southern Cross University of Brazil
Monthly Notices of the Royal Astronomical Society | Year: 2014

Theoretical stellar libraries have been increasingly used to overcome limitations of empirical libraries, e.g. by exploring atmospheric parameter spaces not well represented in the latter. This work presents a new theoretical library which covers 3000 ≤ Teff ≤ 25 000 K,-0.5 ≤ log g ≤ 5.5 and 12 chemical mixtures covering 0.0017 ≤ Z ≤ 0.049 at both scaledsolar and α-enhanced compositions. This library complements previous ones by providing: (i) homogeneous computations of opacity distribution functions, models atmospheres, statistical surface fluxes and high-resolution spectra; (ii) high-resolution spectra with continua slopes corrected by the effect of predicted lines and (iii) two families of α-enhanced mixtures for each scaled-solar iron abundance, to allow studies of the α-enhancement both at 'fixed iron' and 'fixed Z' cases. Comparisons to observed spectra were performed and confirm that the synthetic spectra reproduce well the observations, although there are wavelength regions which should be still improved. The atmospheric parameter scale of the model library was compared to one derived from a widely used empirical library, and no systematic difference between the scales was found. This is particularly reassuring for methods which use synthetic spectra for deriving atmospheric parameters of stars in spectroscopic surveys © 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. Source


Kirby E.N.,California Institute of Technology | Lanfranchi G.A.,Southern Cross University of Brazil | Simon J.D.,Carnegie Institution of Washington | Cohen J.G.,California Institute of Technology | Guhathakurta P.,University of California at Santa Cruz
Astrophysical Journal | Year: 2011

We present metallicity distribution functions (MDFs) for the central regions of eight dwarf satellite galaxies of the Milky Way: Fornax, Leo I and II, Sculptor, Sextans, Draco, Canes Venatici I, and Ursa Minor. We use the published catalog of abundance measurements from the previous paper in this series. The measurements are based on spectral synthesis of iron absorption lines. For each MDF, we determine maximum likelihood fits for Leaky Box, Pre-Enriched, and Extra Gas (wherein the gas supply available for star formation increases before it decreases to zero) analytic models of chemical evolution. Although the models are too simplistic to describe any MDF in detail, a Leaky Box starting from zero metallicity gas fits none of the galaxies except Canes Venatici I well. The MDFs of some galaxies, particularly the more luminous ones, strongly prefer the Extra Gas Model to the other models. Only for Canes Venatici I does the Pre-Enriched Model fit significantly better than the Extra Gas Model. The best-fit effective yields of the less luminous half of our galaxy sample do not exceed 0.02 Z⊙, indicating that gas outflow is important in the chemical evolution of the less luminous galaxies. We surmise that the ratio of the importance of gas infall to gas outflow increases with galaxy luminosity. Strong correlations of average [Fe/H] and metallicity spread with luminosity support this hypothesis. © 2011. The American Astronomical Society. Source


Caproni A.,Southern Cross University of Brazil | Abraham Z.,University of Sao Paulo | Monteiro H.,Federal University of Itajuba
Monthly Notices of the Royal Astronomical Society | Year: 2013

BL Lacertae is the prototype of the BL Lac class of active galactic nuclei, exhibiting intensive activity on parsec (pc) scales, such as intense core variability and multiple ejections of jet components. In particular, in previousworks the existence of precession motions in the pc-scale jet of BL Lacertae has been suggested. In this work we revisit this issue, investigating temporal changes of the observed right ascension and declination offsets of the jet knots in terms of our relativistic jet-precession model. The seven free parameters of our precession model were optimized via a heuristic cross-entropy method, comparing the projected precession helix with the positions of the jet components on the plane of the sky and imposing constraints on their maximum and minimum superluminal velocities. Our optimized best model is compatible with a jet having a bulk velocity of 0.9824c, which is precessing with a period of about 12.1 yr in the observer's reference frame and changing its orientation in relation to the line of sight between 4° and 5°, approximately. Assuming that the jet precession has its origin in a supermassive binary black hole system, we show that the 2.3-yr periodic variation in the structural position angle of the very-long-baseline interferometry (VLBI) core of BL Lacertae reported by Stirling et al. is compatible with a nutation phenomenon if the secondary black hole has a mass higher than about six times that of the primary black hole. © 2012 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. Source


Vinolo M.A.R.,University of Sao Paulo | Hirabara S.M.,Southern Cross University of Brazil | Curi R.,University of Sao Paulo
Current Opinion in Clinical Nutrition and Metabolic Care | Year: 2012

Purpose of review: It has been demonstrated that fatty acids (FAs) are physiological ligands of G-protein-coupled receptors (GPRs). Activation of the GPRs (40, 41, 43, 84, 119 and 120) by FAs or synthetic agonists modulates several responses. In this review, we discuss the current knowledge on the actions of FA-activated GPRs and their relevance in normal and pathological conditions. Recent findings: Studies have shown that FA-activated GPRs modulate hormone secretion (incretin, insulin and glucagon), activation of leukocytes and several aspects of metabolism. Summary: Understanding GPR actions and their involvement in the development of insulin-resistance, β-cell failure, dyslipidemia and inflammation associated with obesity, type 2 diabetes, metabolic syndrome and cardiovascular diseases is important for the comprehension of the mechanisms underlying these pathological conditions and for the establishment of new and effective interventions. © 2012 Wolters Kluwer Health | Lippincott Williams & Wilkins. Source


Coelho P.,Southern Cross University of Brazil | Gadotti D.A.,European Southern Observatory
Astrophysical Journal Letters | Year: 2011

We obtained stellar ages and metallicities via spectrum fitting for a sample of 575 bulges with spectra available from the Sloan Digital Sky Survey. The structural properties of the galaxies have been studied in detail in 2009 by Gadotti and the sample contains 251 bulges in galaxies with bars. Using the whole sample, where galaxy stellar mass distributions for barred and unbarred galaxies are similar, we find that bulges in barred and unbarred galaxies occupy similar loci in the age versus metallicity plane. However, the distribution of bulge ages in barred galaxies shows an excess of populations younger than ∼4 Gyr, when compared to bulges in unbarred galaxies. Kolmogorov-Smirnov statistics confirm that the age distributions are different with a significance of 99.94%. If we select sub-samples for which the bulge stellar mass distributions are similar for barred and unbarred galaxies, this excess vanishes for galaxies with bulge mass log M < 10.1 M ⊙, while for more massive galaxies we find a bimodal bulge age distribution for barred galaxies only, corresponding to two normal distributions with mean ages of 10.4 and 4.7Gyr. We also find twice as much active galactic nuclei among barred galaxies, as compared to unbarred galaxies, for low-mass bulges. By combining a large sample of high-quality data with sophisticated image and spectral analysis, we are able to find evidence that the presence of bars affects the mean stellar ages of bulges. This lends strong support to models in which bars trigger star formation activity in the centers of galaxies. © 2011. The American Astronomical Society. All rights reserved. Source

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