Estrellas Bn: discontinuidad de Balmer; parámetros fundamentales y colores infrarrojos

COCHETTI, Y. R.; ARIAS, M. L.; CIDALE, L. S.; GRANADA, A.; ZOREC, J.

Cordoba

Congreso; 57 Reunion Anual de la Asociacion Argentina de Astronomia; 2014

Bn stars are mainly main sequence objects with B spectral types, thatdisplay in their spectra broad hydrogen lines in absorption. This linebroadening is originated by high rotational velocities. We know thathigh rotation is probably an essential factor in the development of theBe phenomenon: B stars with high rotational velocity and hydrogen linesin emission, which present an extended envelope. Thus, it is interestingto analyze Bn stars in a broader context, that includes Be stars, withthe purpose of investigating their properties, the link between theformation of the envelopes and rotation, and the conditions which definethe presence of emission lines. In this work we study a sample of 62 Bnstar and 70 Be star spectra in the Balmer jump region. We analyze thepresence and intensity of the second Balmer discontinuity, which revealsthe existence of circumstellar material, its correlation with theprojected rotational velocity, V sen(i), and the fundamental parametersof the stars. We also study the distribution of both groups in differentinfrared color-color diagrams, to generate methods to classify them inhighly obscured regions. Our study suggests that Bn stars are the latecounterpart of Be stars. The high projected rotational velocity, thespectral type distribution in both groups, and the presence of Bn starswith a second Balmer discontinuity in absorption, related with densematerial close the photosphere, provide evidence that support thishypothesis.