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Search Results: 1 - 10 of 6689 matches for " Cesar Esteban "
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Massive star formation in Wolf-Rayet galaxies. III: Analysis of the O and WR populations
Angel R. Lopez-Sanchez,Cesar Esteban
Physics , 2010, DOI: 10.1051/0004-6361/200913434
Abstract: (Abridged) We perform a comprehensive multiwavelength analysis of a sample of 20 starburst galaxies that show the presence of a substantial population of Wolf-Rayet (WR) stars. In this paper we present the analysis of the O and WR star populations. We study the spatial localization of the WR-rich clusters via the detection of the blue WR bump (broad He II 4686) and the red WR bump (broad C IV 5808). We perform a detailed fitting of the nebular and broad emission lines within these broad features and derive the numbers of WN, WC and O stars using (i) the standard assumption of constant WR luminosities and (ii) considering metallicity-dependent WR luminosities. We then compare our results with the predictions given by evolutionary synthesis models and with previous empirical results. Aperture effects and the exact positioning of the slit onto the WR-rich bursts play a fundamental role in their detection. As expected, the total number of WR stars increases with increasing metallicity, but objects with 12+log(O/H)<8.2 show a rather constant WR/(WR+O) ratio. The computed WCE/WNL ratios are different than those empirically found in nearby star-forming galaxies, indicating that the observed galaxies are experiencing a strong and very short burst. Considering metallicity-dependent WR luminosities, our data agree with a Salpeter-like IMF in all regimes. We consider that the contribution of the WCE stars is not negligible at low metallicities. Although available models reproduce fairly well the WR properties at high metallicities, new evolutionary synthesis models for young starbursts including all involved parameters (age, metallicity, star-formation history, IMF and WR stars properties such as metallicity-dependent WR luminosities, stellar rotation and the WR binnary channel) are absolutely needed to perform an appropriate comparison with the observational data.
Massive star formation in Wolf-Rayet galaxies: IV b. Using empirical calibrations to compute the oxygen abundance
Angel R. Lopez-Sanchez,Cesar Esteban
Physics , 2010,
Abstract: We have performed a comprehensive multiwavelength analysis of a sample of 20 starburst galaxies that show a substantial population of very young massive stars, most of them classified as Wolf-Rayet (WR) galaxies. We have analysed optical/NIR colours, physical and chemical properties of the ionized gas, stellar, gas and dust content, star-formation rate and interaction degree (among many other galaxy properties) of our galaxy sample using multi-wavelength data. We compile 41 independent star-forming regions --with oxygen abundances between 12+log(O/H) = 7.58 and 8.75--, of which 31 have a direct estimate of the electron temperature of the ionized gas. This paper, only submitted to astro-ph, compiles the most common empirical calibrations to the oxygen abundance, and presents the comparison between the chemical abundances derived in these galaxies using the direct method with those obtained through empirical calibrations, as it is published in Lopez-Sanchez & Esteban (2010b). We find that (i) the Pilyugin method (Pilyugin 2001a,b; Pilyugin & Thuan 2005) which considers the R23 and the P parameters, is the best suited empirical calibration for these star-forming galaxies, (ii) the relations between the oxygen abundance and the N2 or the O3N2 parameters provided by Pettini & Pagel (2004) give acceptable results for objects with 12+log(O/H)>8.0, and (iii) the results provided by empirical calibrations based on photoionization models (McGaugh, 1991; Kewley & Dopita, 2002; Kobulnicky & Kewley, 2004) are systematically 0.2 -- 0.3 dex higher than the values derived from the direct method. These differences are of the same order that the abundance discrepancy found between recombination and collisionally excited lines. This may suggest the existence of temperature fluctuations in the ionized gas, as exists in Galactic and other extragalactic HII regions.
Massive star formation in Wolf-Rayet galaxies. IV: Colours, chemical composition analysis and metallicity-luminosity relations
Angel R. Lopez-Sanchez,Cesar Esteban
Physics , 2010, DOI: 10.1051/0004-6361/201014156
Abstract: (Abridged) We performed a multiwavelength analysis of a sample of starburst galaxies that show the presence of a substantial population of very young massive (WR) stars. Here we present the global analysis of the derived photometric and chemical properties. We compare optical/NIR colours and the physical properties (reddening coefficient, equivalent widths of the emission and underlying absorption lines, ionization degree, electron density, and electron temperature) and chemical properties with previous observations and galaxy evolution models. Attending to their absolute B-magnitude many of them are not dwarf galaxies, but they should be during their quiescent phase. We found that both C(Hb) and Wabs increase with increasing metallicity. We detected a high N/O ratio in objects showing strong WR features. The ejecta of the WR stars may be the origin of the N enrichment in these galaxies. We compared the abundances provided by the direct method with those obtained using empirical calibrations, finding that (i) the Pilyugin method is the best suitable empirical calibration, (ii) the relations between the oxygen abundance and the N2 or the O3N2 parameters provided by Pettini & Pagel (2004) give acceptable results for objects with 12+log(O/H)>8.0, and (iii) the results provided by empirical calibrations based on photoionization models are systematically 0.2-0.3 dex higher than the values derived from the direct method. The O and N abundances and the N/O ratios are related to the optical/NIR luminosity; the dispersion is consequence of the differences in the star-formation histories. Galaxies with redder colours tend to have higher oxygen and nitrogen abundances. Our detailed analysis is fundamental to understand the nature of galaxies showing strong starbursts, as well as to know their star formation history and the relationships with the environment.
Massive star formation in Wolf-Rayet galaxies: II. Optical spectroscopy results
Angel R. Lopez-Sanchez,Cesar Esteban
Physics , 2009, DOI: 10.1051/0004-6361/200912042
Abstract: (Abridged) We have performed a comprehensive multiwavelength analysis of a sample of 20 starburst galaxies that show the presence of a substantial population of very young massive stars. In this paper, the second of the series, we present the results of the analysis of long-slit intermediate-resolution spectroscopy of star-formation bursts for 16 galaxies of our sample. We study the spatial localization of the WR stars in each galaxy. We analyze the excitation mechanism and derive the reddening coefficient, physical conditions and chemical abundances of the ionized gas. We study the kinematics of the ionized gas to check the rotation/turbulence pattern of each system. When possible, tentative estimates of the Keplerian mass of the galaxies have been calculated. Our analysis has revealed that a substantial fraction of the galaxies show evidences of perturbed kinematics. With respect to the results found in individual galaxies, we remark the detection of objects with different metallicity and decoupled kinematics in Haro 15 and Mkn 1199, the finding of evidences of tidal streams in IRAS 08208+2816, Tol 9 and perhaps in SBS 1319+579, and the development of a merging process in SBS 0926+606 A and in Tol 1457-262. All these results reinforce the hypothesis that interactions with or between dwarf objects is a very important mechanism in the triggering of massive star formation in starburst galaxies, specially in dwarf ones. It must be highlighted that only deep and very detailed observationscan provide clear evidences that these subtle interaction processes are taking place.
Jaramillo,Gloria Elena; Quiroz,Juan Esteban; Cartagena,Cesar Augusto; Vivares,Carlos Andrés; Branch,John Willian;
Revista EIA , 2010,
Abstract: with the increasing power and miniaturization of mobile devices, emerging areas of study have found in such devices a new form of visualization and interaction. augmented reality, as a promising metaphor of human-computer interaction, is not the exception. although mobiles do not offer a feasible solution for several general purpose augmented reality applications, due mainly to hardware and processing limitations, some other applications have successfully used them for displaying virtual graphical information within real surroundings. in this paper, experiences gained with the use of augmented reality in mobile devices as a metaphor of visualization are presented. specifically, we focus on the need to preserve cultural heritage and propose augmented reality as an interface for visualizing such cultural material. this paper offers two major contributions: the first one related to the fact of visualizing digitalized heritage of colombian culture by means of an augmented museum and the second one, an enhancement of the user’s experience by displaying detailed reconstructed colombian cultural pieces. we created an augmented museum as a case study and evaluated the viability of using handheld devices for visualization.
Halima Awale,Esteban Falconí-Castillo,Julio Cesar Villatoro-Mérida,James Kelly
Agronomía Mesoamericana , 2008,
Abstract: El objetivo de esta investigación fue determinar la variabilidad patogénica de C. lindemuthianum en zonas productoras de frijol común en Ecuador y Guatemala para identificar las combinaciones de genes de resistencia más efectivas para las condiciones locales. Aislamientos de antracnosis recolectados fueron caracterizados para la identifi cación de las razas presentes en estos países empleando el juego estándar de 12 cultivares diferenciales. De acuerdo a la evaluación, solamente dos razas (5, 9) mostraron estar presentes en los dos países. En Guatemala se registró una mayor diversidad patogénica (mayor número de razas) que en Ecuador. Basados en esta información y en otros datos de estudios realizados anteriormente, sugerimos como la combinación genética más efectiva la piramidación de los genes Co-12 y Co-42. Esta combinación conferiría resistencia completa a casi todas las razas de C. lindemuthianum identifi cadas hasta el momento en los dos países.
Gloria Elena Jaramillo,Juan Esteban Quiroz,Cesar Augusto Cartagena,Carlos Andrés Vivares
Revista EIA , 2010,
Abstract: Con el poder creciente y la miniaturización de los dispositivos móviles, nuevas áreas de estudio han encontrado en esta tecnología una nueva forma de visualización e interacción. La realidad aumentada, como una prometedora metáfora de interacción humano-máquina, no es la excepción. Aunque debido ante todo a limitaciones de procesamiento y hardware, los móviles no ofrecen una solución viable para algunas aplicaciones de realidad aumentada de propósito general, otras aplicaciones los han utilizado con éxito para visualizar información gráfica virtual en entornos reales. En este artículo presentamos experiencias adquiridas con el uso de realidad aumentada en dispositivos móviles como metáfora de la visualización. Específicamente, nos concentramos en la necesidad de preservar el patrimonio cultural para proponer la realidad aumentada como una interfaz para visualizar dicho patrimonio. Este artículo presenta dos aportes principales: el primero, la forma de visualización de patrimonio cultural colombiano y el segundo, una mejora de la experiencia del usuario al presentar piezas culturales colombianas detalladas. Se creó un museo aumentado como caso de estudio y se evalúa la viabilidad del uso de dispositivos de mano para la visualización. Com o poder crescente e a miniaturiza o dos dispositivos móveis, novas áreas de estudo encontraram nesta tecnologia uma nova forma de visualiza o e intera o. A realidade aumentada, como uma prometedora metáfora de intera o humano-máquina, n o é a exce o. Embora devido principalmente a limita es de processamento e hardware, os móveis n o oferecem uma solu o viável para algumas aplica es de realidade aumentada de propósito geral, outras aplica es os utilizaram com sucesso para visualizar informa o gráfica virtual em meios reais. Neste artigo apresentamos experiências adquiridas com o uso de realidade aumentada em dispositivos móveis como metáfora da visualiza o. Especificamente, concentramo-nos na necessidade de preservar o património cultural para propor a realidade aumentada como uma interface para visualizar dito património. Este artigo apresenta duas contribui es principais: a primeira, a forma de visualiza o de património cultural colombiano e a segunda, uma melhora da experiência do usuário ao apresentar pe as culturais colombianas detalhadas. Criou-se um museu aumentado como caso de estudo e avalia-se a viabilidade do uso de dispositivos de m o para a visualiza o. With the increasing power and miniaturization of mobile devices, emerging areas of study have found in such devices a new form of visualization a
The environment of nearby Blue Compact Dwarf Galaxies
Angel R. Lopez-Sanchez,Barbel Koribalski,Janine van Eymeren,Cesar Esteban,Attila Popping,John Hibbard
Physics , 2009,
Abstract: We are obtaining deep multiwavelength data of a sample of nearby blue compact dwarf galaxies (BCDGs) combining broad-band optical/NIR and H$\alpha$ photometry, optical spectroscopy and 21-cm radio observations. Here we present HI results obtained with the Australia Telescope Compact Array for some BCDGs, all showing evident interaction features in their neutral gas component despite the environment in which they reside. Our analysis strongly suggests that interactions with or between low-luminosity dwarf galaxies or HI clouds are the main trigger mechanism of the star-forming bursts in BCDGs; however these dwarf objects are only detected when deep optical images and complementary HI observations are performed. Are therefore BCDGs real isolated systems?
The ionized gas at the center of IC 10: A possible localized chemical pollution by Wolf-Rayet stars
Angel R. Lopez-Sanchez,Adal Mesa-Delgado,Luis Lopez-Martin,Cesar Esteban
Physics , 2010, DOI: 10.1111/j.1365-2966.2010.17847.x
Abstract: We present results from integral field spectroscopy with the Potsdam Multi-Aperture Spectrograph at the 3.5m telescope at Calar Alto Observatory of the intense star-forming region [HL90] 111 at the center of the starburst galaxy IC 10. We have obtained maps with a spatial sampling of 1" x 1" = 3.9 pc x 3.9 pc of different emission lines and analyzed the extinction, physical conditions, nature of the ionization, and chemical abundances of the ionized gas, as well determined locally the age of the most recent star-formation event. By defining several apertures, we study the main integrated properties of some regions within [HL90] 111. Two contiguous spaxels show an unambiguous detection of the broad He II 4686 emission line, this feature seems to be produced by a single WNL star. We also report a probable N and He enrichment in the precise spaxels where the WR features are detected. The enrichment pattern is roughly consistent with that expected for the pollution of the ejecta of a single or a very small number of WR stars. Furthermore, this chemical pollution is very localized (~2"~7.8 pc) and it should be difficult to detect in star-forming galaxies beyond the Local Volume. We also discuss the use of the most-common empirical calibrations to estimate the oxygen abundances of the ionized gas in nearby galaxies from 2D spectroscopic data. The ionization degree of the gas plays an important role when applying these empirical methods, as they tend to give lower oxygen abundances with increasing ionization degree.
Resources to visualize some paradoxes that happens in the planet Mercury
Esteban, Esteban
Revista Eureka sobre Ense?anza y Divulgación de las Ciencias , 2011,
Abstract: En este trabajo se exponen una serie de circunstancias muy curiosas que se producen en el planeta Mercurio, relativas al movimiento del Sol respecto a su horizonte. También se explica la manera de hacer un modelo que permita visualizar algunas de ellas y la forma de escenificar otras.
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