Mecanismo de Fluorescência em Estrelas Simbióticas

Abstract

Symbiotic stars are interacting binary system formed by a cool star (red giant) and a hot companion (white dwarf) accreting the material ejected for its companion by a stellar winds. Based in the cool companion, symbiotic stars are classified between S type (stellar) and D type (dust). In this work, we concentrate our attention in the fluorescence mechanism in symbiotic stars and in the diagnostic diagram based in the lines ratios of the optical spectrum. This diagram is a good tool to separate symbiotic stars and planetary nebulae. On the other hand, the mechanism fluorescence is a important theme in the astrophysical context because it explain the line intensity observed in nebular spectra and allows understanding the forming regions of emission lines. The fluorescence mechanism was applied in the optical spectral region for five S type symbiotic stars to investigate the permitted lines of the double ionized oxygen, OIII, knows as Bowen lines. Our sample consists of the following objects: NSV 11776, Y Cra, V 919 Sgr, KX Tra and CD-43°14304. For each object, we compare the observed lines ratio with the respective theoretic rate and, then, we determine the efficiency of the Bowen fluorescence mechanism in these five symbiotic stars S type, study not available, yet. When observed in the optical region, the spectrum of symbiotic star does not differ of the spectrum of planetary nebulae. Thus, it was propose by workers a diagram diagnostic that separate between this two kind of objects. The diagram is based in the forbidden lines of double ionized oxygen, [OIII], at 4363A and 5007A. Using the spectrum of the five objects studied, we analysed how these stars are distributed by the diagram, in particular for symbiotic star NSV 11776, little studied by workers. For the symbiotic star NSV 11776, we gather the available data in the previous works and we determined physical parameter for this object, as interstellar extinction, electronic temperature and electronic density. Finally, we applied the fluorescent mechanism in the red spectral region for three D-type symbiotic stars: H 1-36, Hen 2-104 e Hen 2-106, to investigate the main excitation mechanism of permitted line of neutral oxygen, OI, at 8446A. According to the developed discussion, the fluorescence mechanism of Lybeta photons of hydrogen Lyman series seems be the main excitation mechanism of OI line in these three symbiotic stars.