1. Question Suppose you examined the spectrum of some nebulosity surrounding a main-sequence spectral-type O star and found that it contained no emission lines, only the continuous spectrum of the star. What conclusions could you draw about the nature of the interstellar material around that star? 2. Relevant Information Was suggested to look at HI regions HII regions dust and how these appear. 3. Attempt at Problem I know O stars are usually hot and produce ionized hydrogen making it an HII region but that also makes strong emission lines from the hydrogen. So it's probably not an HII region. So my next thought is the cloud isn't close enough to be ionized so it's neutral hydrogen and an HI region. Another thought was that it's still an HII region but a reflection nebula and this would keep the continuous spectrum. My biggest issue is that reflection nebulas are usually around cold stars so it may not work out for an O-type star. I'm not sure if I'm missing a key component or if the answer is very obvious and I'm missing it.