THE LIMITED INFLUENCE OF PRESSURE-GRADIENTS ON LATE-TYPE STELLAR LINEASYMMETRIES

Line asymmetries and shifts are powerful tools for studying velocity f ields in the stellar photospheres. Other effects, however, could also generate asymmetries, blurring the information of the velocity pattern s. We have studied the shifts and asymmetries induced in the profiles of spectral lines by pressure effects. The best theoretical and experi mental data on line broadening and shifts caused by collisions with at omic hydrogen were used to analyze the Na I D and three Ca I lines. Li ne bisectors of synthetic spectra computed with accurate data for the Na I and Ca I lines are compared with very high resolution, high signa l-to-noise ratio solar spectra and indicate that pressure broadening r eproduces the wings of the observed lines, but pressure shifts introdu ce neither asymmetries nor shifts comparable to the observed ones.