Which Hydrogen Balmer Lines Are Most Reliable for Determining White Dwarf Atmospheric Parameters?

TL;DR

This study investigates the reliability of different hydrogen Balmer lines in determining white dwarf atmospheric parameters, combining laboratory experiments and theoretical analysis to address discrepancies and improve mass estimates.

Contribution

It highlights potential inaccuracies in theoretical line profiles of Balmer lines and suggests lower-$n$ lines may provide more accurate atmospheric parameters for white dwarfs.

Findings

Discrepancies between H$eta$ and H$ extgamma$ line profiles observed in experiments.

Lower-$n$ Balmer lines may yield more accurate surface gravity estimates.

Implications for white dwarf mass estimates aligning better with gravitational redshift data.

Abstract

Our preliminary results from laboratory experiments studying white dwarf (WD) photospheres show a systematic difference between experimental plasma conditions inferred from measured H$\beta$ absorption line profiles versus those from H$\gamma$. One hypothesis for this discrepancy is an inaccuracy in the relative theoretical line profiles of these two transitions. This is intriguing because atmospheric parameters inferred from H Balmer lines in observed WD spectra show systematic trends such that inferred surface gravities decrease with increasing principal quantum number, $n$. If conditions inferred from lower-$n$ Balmer lines are indeed more accurate, this suggests that spectroscopically determined DA WD masses may be greater than previously thought and in better agreement with the mean mass determined from gravitational redshifts.