9. Concluding remarks
We have presented a theory of self-broadening of hydrogen lines, which includes both resonance and dispersive-inductive interactions. The theory was used to synthesise Balmer lines in cool stars and shown to make a considerable difference compared to the commonly used Ali & Griem (1966) theory which does not include the dispersive-inductive interactions.
The new theory perhaps explains behaviour observed by Gardiner et al. (1999) and Castelli et al. (1997) when using Balmer lines and Ali & Griem (1966) theory to obtain effective temperatures for stars including the sun. It is superior to Ali & Griem (1966) theory when applied to Balmer lines in the solar spectrum as it reduces the discrepancy between observed and computed profiles when the HOLMUL model is used and leads to the KNOVER model being classed as unacceptable both for its failure to adequately model the observed limb darkening and Balmer line profiles. However significant discrepancies between theory and observation for the Balmer lines still exist for the KOVER and HOLMUL models which could be due to our theory or the photospheric models.
Work is in progress on the determination of the effective temperatures of a sample of dwarf stars using our theory and observed Balmer lines for the stars in the sample. Preliminary results indicate a stronger correlation between the effective temperatures obtained from the Balmer lines and the effective temperature obtained by other methods such as the infrared flux method when our theory is used compared with that found when Ali & Griem (1966) theory is used.
We plan to extend the theory to Paschen lines. We expect that in these lines dispersive-inductive interactions will dominate resonance interactions but not Stark broadening. Many of the approximations made in developing the theory are only valid in cool stars with weak quasistatic ion fields. For stars of earlier spectral type it may be necessary to develop a Unified Theory to correctly include self-broadening. The true limit of validity of the impact approximation in H and H needs to be established.
© European Southern Observatory (ESO) 2000
Online publication: December 5, 2000