Iron line cooling of Be star circumstellar discs

We investigate the effect of line cooling due to iron on the predicted temperature distributions in Be star circumstellar envelopes. This analysis is applied to the early-type Be star, gamma Cas, and the late-type Be star, 1 Del, to assess the effect of line cooling due to metals in the circumstellar material over a range of spectral type. We find that iron, and by analogy other abundant metals, can play a role in the energetics of Be star discs by providing both heating from photoionization and cooling by the escape of collisionally excited spectral line radiation. The efficiency of the heating and cooling due to iron varies throughout the circumstellar disc and depends on local physical conditions. Overall, including iron at the solar abundance does not significantly change the volume or density-weighted average temperatures in either gamma Cas or 1 Del from that predicted by a pure hydrogen envelope. However, with an increased iron abundance, to simulate the effect of adding other metals, the temperature variations become more pronounced.