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We report distinctive core profiles in the strongest optical helium line, HeI 5876, from high-resolution high-sensitivity observations of spectral type DBwhite dwarfs. By analyzing a sample of 40 stars from Keck/HIRES and VLT/UVES,we find the core appearance to be related to the degree of hydrogen and heavyelement content in the atmosphere. New Ca K-line measurements or upper limitsare reported for about half the sample stars. He I 5876 emission cores with aself-reversed central component are present for those stars with relatively lowhydrogen abundance, as well as relatively low atmospheric heavy elementpollution. This self-reversed structure disappears for stars with higherdegrees of pollution and/or hydrogen abundance, giving way to a singleabsorption core. From our model atmospheres, we show that the self-reversedemission cores can be explained by temperature inversions in the upperatmosphere. We propose that the transition to a single absorption core is dueto the additional opacity from hydrogen and heavy elements that inhibits thetemperature inversions. Our current models do not exactly match the effectivetemperature range of the phenomenon nor the amplitude of the self-reversedstructure, which is possibly a result of missing physics such as 3D treatment,convective overshoot, and/or non-LTE effects. The He I 5876 line structure mayprove to be a useful new diagnostic for calibrating temperature profiles in DBatmosphere models.

Atmospheric Temperature Inversions and He I 5876 Core Profile Structure in White Dwarfs