Why do O- and B-type stars have weaker hydrogen absorption lines than A-type stars?
A) O- and B-type stars are cooler than A-type stars.
B) O- and B-type stars are smaller than A-type stars.
C) A larger fraction of hydrogen atoms in O- and B-type stars is ionized.
D) O- and B-type stars have converted much more of their hydrogen into heavier elements.
E) A-type stars have a higher mass than O- and B-type stars, so they have more hydrogen.

Question

Quizplus · Accepted Answer

O- and B-type stars are hotter than A-type stars, causing a larger fraction of hydrogen atoms to be ionized, which weakens the hydrogen absorption lines.

Why Do O- and B-Type Stars Have Weaker Hydrogen Absorption