3. Differential abundance analysis
The method of analysis followed closely the procedures discussed by Smartt et al. (1996a, 1996b), where further details can be found. Briefly line-blanketed, plane-parallel model stellar atmospheres in LTE were calculated for each object using the Atlas9 code of Kurucz (1979, 1991). Temperatures, surface gravities, microturbulent velocities and helium abundances were taken from Smartt et al. (1996a). Absolute abundance estimates derived from these model stellar atmospheres were found to be in good agreement with those calculated from a 2-dimensional linear interpolation from a grid of standard model atmospheres as used in Smartt et al. (1996a). Line-by-line differential abundances were determined relative to the same standard as used by Smartt et al. (1996b), namely S285-6. This target was chosen as it has a similar chemical composition to B-type stars observed in the solar neighbourhood (Rolleston et al. 1994). Additionally the high quality of its observational data ensured that it should be a reliable standard in that the large signal to noise ratio in the spectra resulted in accurate equivalent width measurements and hence consistent abundances calculated from the two C II lines.
© European Southern Observatory (ESO) 1998
Online publication: March 23, 1998