CONTRIBUTION FUNCTIONS AND THE DEPTHS OF FORMATION OF SPECTRAL-LINES IN CEPHEIDS

The contribution function of different atmospheric layers to a spectra l line flux depression is derived. Flux contribution contour diagrams based on this function are introduced and are used to model the effect s that pulsational velocity fields have on spectral line formation in a Cepheid atmosphere. In the presence of a constant velocity, the less Doppler-shifted wing of a spectral line is no longer formed at deep a tmospheric layers close to the continuum. The presence of a velocity g radient can have a larger effect on the region of line formation. Mult iple centres of absorption, separated in wavelength and in physical de pth, can occur which will not usually be resolved by observation. The use of spectral lines of different strength and excitation potential t o probe depth-dependent phenomena in pulsating stars will give incorre ct results if based on static model line formation techniques.