The Pseudocontinuum Bound‐Free Opacity of Hydrogen and Its Importance in Cool White Dwarf Atmospheres

We investigate the importance of the pseudo-continuum bound-free opacity fromhydrogen atoms in the atmospheres of cool white dwarfs. This source ofabsorption, when calculated by the occupation probability formalism applied inthe modeling of white dwarf atmospheres with $T_{\rm eff}\rm <17000 K$,dominates all other sources of opacity at optical wavelengths. This isunrealistic and not observed. On the other hand, a significant flux suppressionin the blue part of the spectra of cool white dwarfs has been reported, andmainly interpreted as a result of the pseudo-continuum absorption from atomichydrogen. We investigate this problem by proposing a new, more realisticapproach to calculating this source of opacity. We show that this absorption isorders of magnitude smaller than that predicted by current methods. Therefore,we rule out the pseudo-continuum opacity as a source of the flux deficiencyobserved in the spectra of cool white dwarfs.Comment: 11 pages, 5 gigures, accepted for publication in the Astrophysical Journa