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

TL;DR

This study revisits the pressure and gravitational red shifts of Balmer lines in white dwarfs, using advanced plasma modeling to refine previous estimates and better distinguish between pressure effects and gravitational red shifts.

Contribution

It introduces a modified full computer simulation method to accurately model asymmetrical Stark line profiles in white dwarf atmospheres, improving pressure shift estimates.

Findings

The Stark-induced shift of H_alpha is now found to be about half of previous estimates and negligible compared to gravitational red shift.

The Stark-induced shift of H_beta is about twice larger than earlier estimates due to line asymmetry.

The new modeling reduces uncertainties in measuring gravitational red shifts in white dwarfs.

Abstract

The Stark-induced shift and asymmetry, the so-called pressure shift (PS) of $H_\alpha$ and $H_\beta$ 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 $H_\beta$) 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 $H_\alpha$ line, the present value of Stark-induced shift of the synthetic $H_\alpha$ 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 $H_\beta$ line, the present value of Stark-induced shift of the synthetic $H_\beta$ line-profile is about twice larger than the previous one. The source of this extra shift is the asymmetry of $H_\beta$ peaks.