For Balmer series lines to show up strongly in absorption in stellar spectra,significant numbers of hydrogen atoms have to have electrons in the n = 2 energy level.What then does the appearance of these lines in a stellar spectrum tell us about the temperature of the star's surface?
A) The appearance of the lines tells us very little about the temperature because hydrogen gas will show significant Balmer absorption, whatever the surface temperature.
B) The temperature must be high enough to ionize the hydrogen atoms by collision in order that they can absorb from this level.
C) The temperature must be reasonably low so that no atoms will have electrons excited beyond this energy level (e.g., to n = 3).
D) The temperature must be reasonably high to excite the electrons to this level by collisions, but not high enough to ionize the atoms.

Question

Quizplus · Accepted Answer

The appearance of Balmer series lines in a stellar spectrum tells us that the temperature of the star's surface is reasonably high enough to excite the electrons of hydrogen atoms to the n = 2 level by collisions, but not high enough to ionize the atoms. If the temperature was too low, then the electrons wouldn't be excited beyond the n = 1 level, and if the temperature was too high, then the atoms would be completely ionized, and no absorption lines would be visible. Therefore, the appearance of Balmer series lines can give us an estimate of the temperature of the star's photosphere, which is the layer of the atmosphere that emits most of its visible light.

For Balmer Series Lines to Show Up Strongly in Absorption