# Homework Help: Opacity and Spectral Features

1. Sep 22, 2011

### AnniB

1. The problem statement, all variables and given/known data
If the temperature of a star's atmosphere is increasing outward, what type of spectral feature would one expect to find in the star's spectrum at those wavelengths where the opacity is largest?

2. Relevant equations
Technically n/a

3. The attempt at a solution
I'm pretty sure I know what's going on here, but I want to double check that I don't have my information backwards. I'm thinking that, as temperature increases outward, the flux and luminosity both increase, as would the intensity. Therefore, since intensity decreases as opacity increases (unless my notes are wrong?), then the most opaque material in the star should be at the center (which also, in my mind, makes the most physical sense, but again, I may have all this backwards; I'm not sure). Then, since the highest opacity material would be at the center, the overall spectrum would have absorption lines, as the energy emitted by the particles would be absorbed by the layers above them.

Is that anywhere near correct, or am I completely off-base with my logic?

2. Sep 23, 2011

### chemisttree

I think your logic is off a bit. Think of the various layers of the sun like layers of an onion. The temperature brightness of these layers is increasing as you move outward. At some point you have an opaque layer that blocks the light from the interior somewhat. What causes this opacity? What physical process would absorb the light energy? What spectral feature would you see for the opaque layer?