We report on low resolution (R~3000) spectropolarimetry of the A0 supergiant star HD 92207. This star is well-known for significant spectral variability. The source was observed on seven different nights spanning approximately 3 months in time. With a rotation period of approximately 1 year, our data covers approximately a quarter of the star's rotational phase. Variability in the continuum polarization level is observed over this period of time. The polarization across the Halpha line on any given night is typically different from the degree and position angle of the polarization in the continuum. Interestingly, Hbeta is not in emission and does not show polarimetric variability. We associate the changes at Halpha as arising in the wind, which is in accord with the observed changes in the profile shape and equivalent width of Halpha along with the polarimetric variability. For the continuum polarization, we explore a spiral shaped wind density enhancement in the equatorial plane of the star, in keeping with the suggestion of Kaufer etal (1997). Variable polarization signatures across Halpha are too complex to be explained by this simple model and will require a more intensive polarimetric follow-up study to interpret properly.

Made available in DSpace on 2015-03-03T15:15:27Z (GMT). No. of bitstreams: 1 TharcisyoSSD_DISSERT.pdf: 3303211 bytes, checksum: cec9a1421d7e1a74109ea2385531baa3 (MD5) Previous issue date: 2012-03-02 / This study proposes an observing program focused on the investigation of the stellar magnetism and dynamo evolution in cool active solar-like stars. More mainly in the solar analogs and twins. Observations of stars of our base were carried out with two spectropolarimeter (ESPaDOnS@CFHT and NARVAL@TBL). The analyse of stars in stage different allows an understanding of the dependence of magnetic activity on basic stellar parameters such as rotation, mass, age and depth of the convection zone. This study provides measures necessary for testing dynamo theories. The 65 targets for this project are solar type stars with mass spanning from 0:9 M=Mfi 1:075 solar masses and at different evolutionary stages. Our two main science objectives were, (i) To determine how the magnetic field evolved from the ZAMS to the TO (turn off) for stars with 0:9 M=Mfi 1:075; (ii) To determine the impact of convective depth and rotation on magnetic of cool stars of solar type. The main result from this study was the characterization of the dependence of magnetic field intensity as function of age, Rossby number and the convective zone deepening. This context, the availability of ESPaDOnS and NARVAL opens an exceptional possibility to study the magnetic properties of Sun-like stars by means of spectropolarimetric observations / Este estudo prop?e um programa observacional focado na investiga??o da evolu??o do magnetismo estelar e do d?namo em estrelas frias, ativas e do tipo-solar. Mais precisamente nas estrelas an?logas e g?meas solares. As observa??es das estrelas da nossa base foram realizadas com dois espectropolar?metros (ESPaDOnS@CFHT e NARVAL@TBL). A an?lise das estrelas em diferentes est?gios permite uma compreens?o da depend?ncia da atividade magn?tica em fun??o de par?metros estelares b?sicos como, por exemplo, a rota??o, a massa, a profundidade da zona convectiva e a idade. Este estudo fornece medidas necess?rias para testar ? teoria do d?namo. Os 65 objetos utilizados nesse trabalho tratam-se de estrelas do tipo solar, com massa no intervalo de 0:9 < M=M < 1:075 e em diferentes est?gios evolutivos. Nossos dois principais objetivos cient?ficos foram, (i) Determinar como o campo magn?tico evoluiu a partir da sequ?ncia principal de idade zero (ZAMS) at? o turn off, num intervalo de massa 0:9<M=M,<1:075; (ii) Determinar o impacto da profundidade da zona convectiva e da rota??o no magnetismo das estrelas frias do tipo solar. O principal resultado deste estudo foi a caracteriza??o da depend?ncia da intensidade do campo magn?tico com a idade, com o n?mero de Rossby e com o aprofundamento da zona convectiva. Neste contexto, a disponibilidade do ESPaDOnS e NARVAL abre uma excepcional possibilidade para estudarmos as propriedades magn?ticas das estrelas do tipo-solar atrav?s das observa??es espectropolarim?tricas.