The second Balmer discontinuity in early type stars.

CRUZADO, A.; VAZQUEZ, A.; RINGUELET, A.

Córdoba, Argentina

Congreso; 49º Reunión Anual de la Asociación Argentina de Astronomía.; 2006

Asociación Argentina de Astronomía.

The purpose of this work is to search for theoretical correlations between the size of the Balmer Discontinuity (BD) and the thermodynamical state of the circumstellar material that sourrounds early type stars. By applying the Implicit Integral Method, the tranfer equation is solved in spherical geometry, consistently with the statistical equilibrium equations for different distributions of density and temperature in the medium. We obtain the emergent flux as a function of the wavelength together with the state of the material throughout the stellar photosphere and the circumstellar envelope. We distinguish between the photospheric component of the BD, D*, and the circumstellar one, d. The parameter A=N2/N3/(N2/N3)*, which represents the departure from LTE of the ratio of the n=2 to the n=3 hydrogen levels population, is calculated as a function of the distance to the central star. The component d is obtained as a function of the average of A, and also as a function of the column density of free electrons (Nec). Our conclusion is that a second Balmer jump in absorption is observed only for very low temperatures in the circumstellar envelope; that is electron temperature values lower than 5000K. Otherwise, a second Balmer jump in emission is present. A constraint on the column of free electrons can be also set: Nec/R* higher than 10E12 particles per volume unit for a second Balmer jump to be observed, either in emission or absorption.