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We used a set of moderately-deep and high-resolution optical observations obtained with the Hubble Space Telescope to investigate the properties of the stellar population in the heavily obscured bulge globular cluster NGC 6256. The analysis of the color-magnitude diagram revealed a stellar population with an extended blue horizontal branch and severely affected by differential reddening, which was corrected taking into account color excess variations up to \delta E(B-V) ~ 0.51. We implemented a Monte Carlo Markov Chain technique to perform the isochrone fitting of the observed color-magnitude diagram in order to derive the stellar age, the cluster distance and the average color excess in the cluster direction. Using different set of isochrones we found that NGC 6256 is characterized by a very old stellar age around 13.0 Gyr, with a typical uncertainty of ~ 0.5 Gyr. We also found an average color excess E(B-V) = 1.19 and a distance from the Sun of 6.8 kpc. We then derived the cluster gravitational center and measured its absolute proper motion using the Gaia-DR2 catalog. All this was used to back-integrate the cluster orbit in a Galaxy-like potential and measure its integrals of motion. It turned out that NGC 6256 is currently in a low-eccentricity orbit entirely confined within the bulge and its integrals of motion are fully compatible with a cluster purely belonging to the Galaxy native globular cluster population. All these pieces of evidence suggest that NGC 6256 is an extremely old relic of the past history of the Galaxy, formed during the very first stages of its assembly., Comment: Accepted for publication by ApJ

Submitted by Joelma Souza de Oliveira (id.joelma7@gmail.com) on 2019-07-24T21:52:53Z No. of bitstreams: 1 Disserta??o-Tereza-Torres.pdf: 14724744 bytes, checksum: 8f8a74358ef491745c98d69fe63d0f04 (MD5) Made available in DSpace on 2019-07-24T21:52:53Z (GMT). No. of bitstreams: 1 Disserta??o-Tereza-Torres.pdf: 14724744 bytes, checksum: 8f8a74358ef491745c98d69fe63d0f04 (MD5) Previous issue date: 2018-06-18 Funda??o de Amparo ? Pesquisa do Estado da Bahia - FAPEB The accuracy and precision of cosmological results obtained from studies of Type Ia supernovae (SNe Ia) strongly depend on the control of systematic uncertainties. The modeling of both Galactic and the host galaxy extinction is a critical step in characterizing supernovae effects, thus its improvement can provide a significantly better way of their usage. Using the Cardelli, Clayton & Mathis (CCM) extinction law we have elaborated a method for reproducing the observed SN spectra by adjusting five parameters, namely Av and Rv for both Milky Way and SN host galaxy, also the SN redshift. In this manner, the fine tuning for both Galactic and the host galaxy extinction is achieved. We have used two different SNe Ia templates and the Harvard-Smithsonian Center for Astrophysics (CfA) supernova catalogue with more than 2600 SNe Ia observed spectra. The comparisons of the modeled spectra with the observed ones are presented, and the obtained parameters are thoroughly discussed. We have estimated parameters for 80 SNe Ia, covering 1080 spectra with epochs ranging from -20 to 50 days. A precis?o de resultados cosmol?gicos obtidos a partir de estudos de supernovas Tipo Ia (SNas Ia) dependem fortemente do controle de incertezas sistem?ticas. Tanto a modelagem da extin??o Gal?ctica quanto da gal?xia hospedeira ? algo fundamental na caracteriza??o dos efeitos observados em supernovas, portanto, o seu bom modelamento pode proporcionar uma maneira mais adequada de comprendermos os aspectos f?sicos envolvidos. Usando a lei de extin??o de Cardelli, Clayton e Mathis (CCM) foi elaborado um m?todo para reproduzir os espectros observados de supernovas por meio do ajuste de cinco par?metros, a extin??o total (AV) e a raz?o entre a extin??o total e a seletiva (RV), tanto para a Via L?ctea como para a gal?xia hospedeira da SNa, assim como o redshift da SNa. Dessa forma, foram encontrados os melhores valores da extin??o e do redsfhit para reproduzir o espectro observado. Foram utilizados dois templates diferentes de SNas Ia (Hsiao e SALT) e o Cat?logo de supernovas Harvard-Smithsonian Center for Astrophysics (CfA) com mais de 2600 espectros observados de SNas Ia. As compara??es dos espectros modelados com os observados s?o apresentadas e os par?metros obtidos s?o discutidos de forma detalhada. Foram obtidos os par?metros para 80 SNas Ia, abrangendo 1080 espectros com ?pocas variando entre -20 a 50 dias. A compara??o com os valores dispon?veis na literatura mostram uma concord?ncia entre os resultados obtidos no presente trabalho e os obtidos por outros autores.

Results of comparison of Gaia DR2 parallaxes with data derived from a combined analysis of 2MASS (Two Micron All-Sky Survey), SDSS (Sloan Digital Sky Survey), GALEX (Galaxy Evolution Explorer), and UKIDSS (UKIRT Infrared Deep Sky Survey) surveys in four selected high-latitude | b | &gt, 48&deg, sky areas are presented. It is shown that multicolor photometric data from large modern surveys can be used for parameterization of stars closer than 4400 pc and brighter than g S D S S = 19 . m 6 , including estimation of parallax and interstellar extinction value. However, the stellar luminosity class should be properly determined.