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) A larger fraction of hydrogen atoms in O- and B-type stars is ionized.
C) O- and B-type stars have converted much more of their hydrogen into heavier elements.
D) A-type stars have a higher mass than O- and B-type stars and they have more hydrogen.

Question

Quizplus · Accepted Answer

O- and B-type stars have higher temperatures than A-type stars, which should give stronger hydrogen absorption lines. However, these stars also have stronger ionizing radiation that can ionize hydrogen atoms, leading to weaker hydrogen absorption lines. This results in a higher fraction of hydrogen atoms being ionized in O- and B-type stars, leading to weaker hydrogen absorption lines compared to A-type stars.

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