Of two stars of spectral class B5,one has broad hydrogen lines and the other has narrow hydrogen lines.How do these stars differ physically?
A) The star with the narrow lines is a main-sequence star,and the star with the broad lines is a giant or supergiant.
B) The star with the narrow lines is a hot star,and the star with the broad lines is a cool star.
C) The star with the narrow lines is a giant or supergiant,and the star with the broad lines is a main-sequence star.
D) The star with the narrow lines is a cool star,and the star with the broad lines is a hot star.

Question

Quizplus · Accepted Answer

The star with narrow hydrogen lines is a giant or supergiant, while the star with broad hydrogen lines is a main-sequence star. Narrow lines indicate that the gas around the star is moving slowly, which is consistent with the low surface gravity of a giant or supergiant star. On the other hand, the broad lines indicate high-speed motion due to the surface gravity of a main-sequence star. Both stars have the same spectral class (B5), which means they have similar temperatures and are both hot stars.

Of Two Stars of Spectral Class B5,one Has Broad Hydrogen