Absorption line strengths are used in the spectral classification of stars and the determination of surface temperatures. Which of these atomic or molecular constituents exhibits strong absorption lines in spectra from stars with very high surface temperature?
A) H
B) Ca II
C) He II
D) TiO

Question

Quizplus · Accepted Answer

He II (Helium II) exhibits strong absorption lines in the spectra from stars with very high surface temperatures. This is because the ionization energy required to form He II (removing a second electron from helium) is very high, and such conditions are typically found only in the atmospheres of very hot stars.

Absorption Line Strengths Are Used in the Spectral Classification of Stars