Excitation of Sr II lines in Eta Carinae

Abstract:
We study the nature of the peculiar [Sr II] and Sr II emission filament found in the ejecta of Eta Carinae. To this purpose we carry out abinitio calculations of radiative transition probabilities and electron impact excitation rate coefficients for Sr II. Then we build a multilevel model for the system which is used to investigate the physical condition of the filament and the nature of the observed allowed and forbidden Sr II optical emission. It is found that the observed spectrum is consistent with the lines being pumped by the continuum radiation field in a mostly neutral region with electron density near 10<SUP>7</SUP>cm<SUP>-3</SUP> . Under these conditions, the observed emission can be explained without the need for a large Sr overabundance.