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Previous issue date: 2008-12-22 === In the present work, we have studied the nature of the physical processes of the coronal heating, considering as basis significant samples of single and binary evolved
stars, that have been achieved with the ROSAT satellite. In a total of 191 simple stars were studied, classified in the literature as giants with spectral type F, G and K. The
results were compared with those obtained from 106 evolved stars of spectral type F, G and K, which belong to the spectroscopic binary systems. Accurate measurements
on rotation and information about binarity were obtained from De Medeiros s catalog. We have analysed the behavior of the coronal activity in function of diverse
stellar parameters. With the purpose to better clarify the profile of the stars evolution, the HR diagram was built for the two samples of stars, the single and the binary ones.
The evolved traces added in the diagram were obtained from the Toulouse-Geneve code, Nascimento et al. (2000). The stars were segregated in this diagram not only in range of rotational speed but also in range of X-ray flux. Our analysis shows clearly that the single stars and the binary ones have coronal activity controlled by physical process independent on the rotation. Non magnetic processes seem to be strongly influencing the coronal heating. For the binary stars, we have also studied the behavior of the coronal emission as a function of orbital parameters, such as period and eccentricity, in
which it was revealed the existence of a discontinuity in the emission of X-rays around an orbital period of 100 days. The study helped to conclude that circular orbits of the binary stars are presented as a necessary property for the existence of a higher level ofX-rays emission, suggesting that the effect of the gravitational tide has an important role in the coronal activity level. When applied the Kolmogorov-Smirnov test (KS test ) for the Vsini and FX parameters to the samples of single and binary stars, we could evidence very relevant aspects for the understanding of the mechanisms inherent to the coronal activity. For the Vsini parameter, the differences between the single stars and the binary ones for rotation over 6.3 km/s were really remarkable. We believe, therefore, that the existence of gravitational tide is, at least, one of the factors that most contribute for this behavior. About the X-rays flux, the KS test showed that the behavior of the single and the binary stars, regarding the coronal activity, comes from the same origin === No presente trabalho, estudamos a natureza dos processos f?sicos do aquecimento coronal, tomando como base amostras significativas de estrelas evolu?das simples e bin?rias, obtidas com o sat?lite ROSAT. No total, foram estudadas 191 estrelas simples, classificadas na literatura como gigantes com tipo espectral F, G e K. Os resultados foram comparados com os obtidos das 106 estrelas evolu?das de tipo espectral F, G e K pertencentes a sistemas bin?rios espectrosc?picos. Medidas precisas sobre rota??o e informa??es sobre binaridade foram obtidas do cat?logo de De Medeiros. Analisamos o comportamento da atividade coronal em fun??o de diversos par?metros estelares. Para uma maior clareza do perfil de evolu??o das estrelas foi constru?do
o diagrama HR para as duas amostras de estrelas, as simples e as bin?rias. Os tra?ados evolutivos adicionados nos diagramas foram obtidos a partir do c?digo de Toulouse-Geneve, Nascimento et al. (2000). As estrelas foram segregadas nesse diagrama tanto por intervalo de velocidade rotacional como por intervalo de fluxo de raio-X. Nossa an?lise mostra claramente que as estrelas simples e as bin?rias possuem atividade coronal dominada por processo f?sico independente da rota??o. Processos n?o magn?ticos parecem estar influenciando fortemente o aquecimento coronal. Para as estrelas bin?rias, estudamos ainda o comportamento da emiss?o coronal em fun??o de par?metros orbitais, como per?odo e excentricidade, tendo sido revelada a exist?ncia de uma descontinuidade na emiss?o de raio-X em torno de um per?odo orbital de 100 dias. O estudo permitiu concluir que a circulariza??o das ?rbitas das estrelas bin?riasapresenta-se como uma propriedade necess?ria para a exist?ncia de um n?vel de emiss?o de raio-X mais elevado, sugerindo que efeito de mar? gravitacional tem importante papel no n?vel de atividade coronal. Ao aplicarmos o teste Kolmogorov-Smirnov (teste KS) para os par?metros Vsini e FX ?s amostras de estrelas simples e bin?rias, evidenciamos aspectos bastante relevantes para a compreens?o dos mecanismos inerentes ? atividade coronal. Para a grandeza Vsini, ficaram marcantes as diferen?as existentes entre as estrelas simples e as bin?rias para rota??es acima de 6,3 km/s. Acreditamos, pois, ser a exist?ncia de mar? gravitacional, pelo menos, um dos fatores que contribui para esse comportamento. Quanto ao fluxo de raio-X, o teste KS demonstrou que o comportamento das estrelas simples e bin?rias, no que diz respeito ? atividade coronal, prov?m de uma mesma origem
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