Pressure Shift and Gravitational Red Shift of Balmer Lines in White Dwarfs. Rediscussion

The Stark-induced shift and asymmetry, the so-called pressure shift (PS) of $H_α$ and $H_β$ Balmer lines in spectra of DA white dwarfs (WDs), as masking effects in measurements of the gravitational red shift in WDs, have been examined in detail. The results are compared with our earlier ones from before a quarter of a century (Grabowski et al. 1987, hereafter ApJ'87; Madej and Grabowski 1990). In these earlier papers, as a dominant constituent of the Balmer-line-profiles, the standard, symmetrical Stark line profiles, shifted as the whole by PS-effect, were applied to all spectrally active layers of the WD atmosphere. At present, in each of the WD layers, the Stark-line-profiles (especially of $H_β$) are immanently asymmetrical and shifted due to the effects of strong inhomogeneity of the perturbing fields in plasma. To calculate the Stark line-profiles in successive layers of the WD atmosphere we used the modified Full Computer Simulation Method (mFCSM), able to take adequately into account the complexity of local elementary quantum processes in plasma. In the case of the $H_α$ line, the present value of Stark-induced shift of the synthetic $H_α$ line-profile is about twice smaller than the previous one (ApJ'87) and it is negligible in comparison with the gravitational red shift. In the case of the $H_β$ line, the present value of Stark-induced shift of the synthetic $H_β$ line-profile is about twice larger than the previous one. The source of this extra shift is the asymmetry of $H_β$ peaks.

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