Question

Consider the strength of the Hβ absorption line in the spectra of stars of various surface temperatures. This is the amount of light that is missing from the spectra because Hydrogen electrons have absorbed the photons and jumped from level 2 to level 4. How do you think the strength of Hβ absorption varies with stellar surface temperature?

Answer 1

The strength and absorption of Hβ lines varies with stellar surface temperature. And due to this, we can determine the temperature of a star from their strength and absorption lines.

To understand this, we need the concept of atomic structure of atom. Atoms have different levels of energy and these energy levels are fixed (cannot be changed by temperature). Temperature certainly does effect the number of electrons in those energy levels. So to produce a hydrogen absorption line in the visible band of electromagnetic spectrum, we need the electron in the second energy level when it absorbs a photon.

So when electons jumped from level 2 to level 4 by absorbing a photons, it simply means the temperature of the stellar surface has increased and the strength of the Hβ lines will decrease (but still detectable H lines). If the surface temperature becomes too-hot, then there is no electron bound to hydrogen atom and there will be no H lines. And if the surface temperature becomes too-cold, that means, electron is stuck in the ground state and there will be no H lines.

So, to get a very strong H lines, most electron should be in the 2nd energy level after absorbing photons.

I have tried to solve step-by-step. Hope you like it. Thanks for asking questions.