How can we explain the fact that hydrogen Balmer lines are essentially absent in the hot O type and the cool M stars?
A) O type stars do not contain hydrogen.
B) In cool stars hydrogen combines to form large molecules.
C) In O stars hydrogen is ionized and in M stars the electrons of hydrogen are in level 1, not level 2.
D) All of these choices are correct.

Question

Quizplus · Accepted Answer

In O type stars, the high temperatures cause hydrogen to be ionized, preventing the formation of Balmer lines. In M type stars, the temperatures are too low to excite electrons to the second energy level, which is necessary for Balmer line formation.

How Can We Explain the Fact That Hydrogen Balmer Lines