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Fusco F.,University of Rome Tor Vergata | Buonanno R.,University of Rome Tor Vergata | Buonanno R.,National institute for astrophysics | Bono G.,University of Rome Tor Vergata | And 4 more authors.
Astronomy and Astrophysics | Year: 2012

On the basis of a new photometric analysis of the Local Group dwarf irregular galaxy NCG 6822 based on observations obtained with the Advanced Camera for Surveys onboard the Hubble Space Telescope, we have obtained a new estimate of the extinction of two fields located in the southeast region of the galaxy. Because of significant differences in the distance estimates to NGC 6822 available in literature, we decided to provide an independent determination of the distance to this galaxy based on an updated and self-consistent theoretical calibration of the tip of the red giant branch brightness. As a result we newly determined the distance to NGC 6822 to be equal to (m-M)0 = 23.54 ± 0.05, and compared our measurement with the most recent determinations of this distance. © 2012 ESO. Source

Tapia M.T.,Instituto Astrofisico Of Canarias | Tapia M.T.,National Autonomous University of Mexico | Tapia M.T.,Autonomous University of Baja California | Schuster W.J.,National Autonomous University of Mexico | And 5 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2010

The three open clusters Be 15, Be 80 and NGC 2192 have been observed using CCD UBV(RI)C photometry at the San Pedro Mártir Observatory, México within the framework of our open-cluster survey. The fundamental parameters of interstellar reddening, distance and age have been derived, and also the metallicity for NGC 2192 (solar metallicity has been assumed for the other two). By shifting the colours of Schmidt-Kaler in the (U - B, B - V) two-colour diagram along the appropriate reddening vector, the interstellar reddenings have been derived as E(B - V) = 0.23 ± 0.03 mag for Be 15, 1.31 ± 0.05 for Be 80, and 0.16 ± 0.03 for NGC 2192. Evidence is shown for a variable interstellar extinction across the cluster Be 80. For NGC 2192, a nicely consistent fit is obtained for both the interstellar reddening and the metallicity ([Fe/H] = -0.31) using simultaneously the F-type and red-clump stars. By fitting isochrones to the observed sequences of these three clusters in various colour-magnitude diagrams of different colour indices (B - V, V - I or V - R), the averages of distance moduli and heliocentric distances [(V - MV)o (mag); d(pc)] are the following: (10.74 ± 0.01; 1202) for Be 15, (10.75 ± 0.01; 1413) for Be 80 and (12.7 ± 0.01; 3467) for NGC 2192, and the averages of the inferred best ages [log(age); age(Gyr)] are (8.6 ± 0.05; 0.4) for Be 80 and (9.15 ± 0.05; 1.4) for NGC 2192; for Be 15 there are two distinct possibilities for the age fit, depending on the membership of three brighter stars (9.35 or 9.95 ± 0.05; 2.2 or 8.9). The need for spectroscopic observations in Be 15 is emphasized to select between alternate reddening and age solutions, and for deeper UBV observations in Be 80 to study in greater detail the variable interstellar, or intracluster, reddening across this cluster. © 2009 RAS. Source

Corsini E.M.,University of Padua | Corsini E.M.,National institute for astrophysics | Mendez-Abreu J.,Instituto Astrofisico Of Canarias | Mendez-Abreu J.,University of La Laguna | And 11 more authors.
Monthly Notices of the Royal Astronomical Society: Letters | Year: 2012

The early-type spiral NGC4698 is known to host a nuclear disc of gas and stars which is rotating perpendicularly with respect to the galaxy main disc. In addition, the bulge and main disc are characterized by a remarkable geometrical decoupling. Indeed, they appear elongated orthogonally to each other. In this work, the complex structure of the galaxy is investigated by a detailed photometric decomposition of optical and near-infrared images. The intrinsic shape of the bulge was constrained from its apparent ellipticity, its twist angle with respect to the major axis of the main disc and the inclination of the main disc. The bulge is actually elongated perpendicular to the main disc and it is equally likely to be triaxial or axisymmetric. The central surface brightness, scalelength, inclination and position angle of the nuclear disc were derived by assuming that it is infinitesimally thin and exponential. Its size, orientation and location do not depend on the observed passband. These findings support a scenario in which the nuclear disc is the end result of the acquisition of external gas by the pre-existing triaxial bulge on the principal plane perpendicular to its shortest axis and perpendicular to the galaxy main disc. The subsequent star formation either occurred homogeneously all over the extension of the nuclear disc or through an inside-out process that ended more than 5 Gyr ago. © 2012 The Authors. Monthly Notices of the Royal Astronomical Society. © 2012 RAS. Source

Pietrinferni A.,National institute for astrophysics | Cassisi S.,National institute for astrophysics | Salaris M.,Liverpool John Moores University | Hidalgo S.,Instituto Astrofisico Of Canarias
Astronomy and Astrophysics | Year: 2013

We present an extension of the BaSTI (Bag of Stellar Tracks and Isochrones) stellar evolution database to extremely metal-poor (Z = 10-5) and super-metal-rich (Z = 0.05) metallicities, with both scaled-solar and α-enhanced ([α/Fe] = 0.4) heavy element distributions. These new tracks (from the pre-main sequence to the early-asymptotic giant branch phase), horizontal branch models, and isochrones will enable the use of the BaSTI database to study the most metal-poor populations found in Local Group faint dwarf galaxies, and the metal-rich component of the Galactic bulge, for example. An overview of several fundamental predictions of stellar evolution over the full metallicity range of BaSTI is presented, together with comparisons with literature calculations at Z = 10-5 and Z = 0.05. © ESO, 2013. Source

Mendez-Abreu J.,Instituto Astrofisico Of Canarias | Mendez-Abreu J.,University of La Laguna
Revista Mexicana de Astronomia y Astrofisica: Serie de Conferencias | Year: 2013

We investigate the suitability of GTC/OSIRIS Tunable Filters (TFs) for obtaining emission-line maps of extended objects. We developed a technique to reconstruct an emission-line image from a set of images taken at consecutive central wavelengths. We demonstrate the feasibility of the reconstruction method by generating a flux calibrated Hα image of the well-known spiral galaxy M101. We tested our emission-line fluxes and ratios by using data present in the literature. We found that the differences in both Hα fluxes and N II/Hα line ratios are ∼15% and ∼50%, respectively. These results are fully in agreement with the expected values for our observational setup. The proposed methodology will allow us to use OSIRIS/GTC to perform accurate spectrophotometric studies of extended galaxies in the local Universe. © 2013: Instituto de Astronomía, UNAM - Fourth Science Meeting with the GTC Ed. C. Muñoz-Tuñón & J. M. Rodríguez-Espinosa. Source

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