What spectral lines are strongest in B-type stars?

In B-type stars, the strongest spectral lines are indeed the He I absorption lines. B-type stars, which are classified as having surface temperatures ranging from approximately 10,000 to 30,000 Kelvin, exhibit blue-white colors due to their high temperature and energy output.

The physical conditions in B-type stars allow for the presence of neutral helium (He I) in the outer atmosphere, which absorbs light at specific wavelengths. When these stars are analyzed through spectroscopy, the He I lines appear prominently in their spectra because the density and energy conditions in B-type stars favor the creation of neutral helium ions that absorb light at particular wavelengths.

In contrast, He II lines are found in even hotter stars, primarily O-type stars, while absorption lines from calcium (Ca II) and the Balmer series (which involves hydrogen) typically show stronger signatures in cooler stars, such as A-type or G-type stars. Thus, the prominence of the He I spectral lines in B-type stars aligns with their physical properties and the conditions that prevail in their stellar atmospheres.