Spectrum of hot gas uniformly mixed with dust

  • #1
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hey!

EDIT: I didn’t post this in homework help because there aren’t any computational questions, it’s just conceptual

My assignment scenario consists of a star (blackbody) surrounded by an expanding shell of hot gas. I’m given its spectrum and it is a continuous emission spectrum. Emission due to the hot gas and continuous due to the blackbody hidden behind the hot gas.

Now I’m told to assume that dust has been uniformly mixed into the shell of hot gas. I have to draw the spectrum for this scenario. (I’m not sure if I did this right. I’m probably misreading the graph. )I know that blue light is scattered more than red and the light would dim because I’d the dust.

I did drew a continuous spectrum, however I lowered the peak and the blue wavelength (left) side of the spectrum as well as the red wavelength side of the spectrum, however the red side was higher than the blue side.

The darker line is what I drew, and the lighter one is what I was given. I’m almost certain this is incorrect because I don’t really understand what dust does to spectra.
 

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  • #2
stefan r
Science Advisor
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Dust particles adsorb (or scatter) wavelengths that are shorter than the diameter of the dust grain. The question should have more information about the dust.

A coffee mug can block visual radiation and 10 cm radiation. 1 m radiation passes it. A sphere of coffee mugs will have a slight anomaly because the handles block extra 3cm radiation. Glass beer mugs would be similar to the coffee mugs but let visual light through. You can get away with assuming everything is a sphere.

hey!

EDIT: I didn’t post this in homework help because there aren’t any computational questions, it’s just conceptual

My assignment scenario consists ...
This is clearly a homework question.
 
  • #3
Drakkith
Staff Emeritus
Science Advisor
21,105
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The darker line is what I drew, and the lighter one is what I was given. I’m almost certain this is incorrect because I don’t really understand what dust does to spectra.
What does your book or lecture notes say about what effect the dust has?
 
  • #4
184
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What does your book or lecture notes say about what effect the dust has?
All my lecture notes say is that dust would dim the light and make it appear redder. Due to this, I first drew my spectrum redshifted, confusing colour with the redshift (oops) but then my professor said to think about what happens to light in dust. My lecture notes also say that dust scatters blue light so I drew the whole spectrum with less flux (dimmer) and then made the blue wavelength side of my spectrum smaller than the red wavelength side (or at least I tried to) and have no idea if this was right.

We don’t have a book for the course, just lecture notes.

It doesn’t say the dust was cool so I assumed no absorption spectra.
 
  • #5
184
8
Dust particles adsorb (or scatter) wavelengths that are shorter than the diameter of the dust grain. The question should have more information about the dust.

A coffee mug can block visual radiation and 10 cm radiation. 1 m radiation passes it. A sphere of coffee mugs will have a slight anomaly because the handles block extra 3cm radiation. Glass beer mugs would be similar to the coffee mugs but let visual light through. You can get away with assuming everything is a sphere.



This is clearly a homework question.
There was no other information besides that it was uniformly mixed into the expanding shell of hot gas
 
  • #6
Drakkith
Staff Emeritus
Science Advisor
21,105
4,934
All my lecture notes say is that dust would dim the light and make it appear redder. Due to this, I first drew my spectrum redshifted, confusing colour with the redshift (oops) but then my professor said to think about what happens to light in dust. My lecture notes also say that dust scatters blue light so I drew the whole spectrum with less flux (dimmer) and then made the blue wavelength side of my spectrum smaller than the red wavelength side (or at least I tried to) and have no idea if this was right.

We don’t have a book for the course, just lecture notes.

It doesn’t say the dust was cool so I assumed no absorption spectra.
That looks correct to me, and seems to match up with what your lecture notes say.
 
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