Which spectral class exhibits the strongest Balmer lines (hydrogen absorption)?
Answer
A-type stars
A-type stars are characterized by having the strongest Balmer lines, which are absorption lines caused by hydrogen in the star's atmosphere. This peak strength occurs because the temperature of an A-type star is optimal for exciting hydrogen atoms to the precise energy levels required to produce these specific absorption features. If the star is significantly hotter (like B or O types), the hydrogen atoms become nearly entirely ionized, meaning there are few neutral atoms left to absorb photons, thus weakening the lines. Conversely, if the star is cooler (like F or G types), the atoms are not excited enough to produce the strong Balmer signature.
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