Emissivity of dust grains

In summary, the author says that the dust shell model is consistent with the observed shape of the IR excess and the observed size of the 60 micrometer source. Since ##\varepsilon_\text{vis}## for most material is near unity, it follows that ##\varepsilon_\text{IR}## also has to be near unity. This condition will normally be satisfied if the particle radius, ##a##, is comparable to or larger than ##\lambda_p / 2\pi##, where ##\lambda_p## is the wavelength of the peak emission.
  • #1
robotopia
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0
In this 1984 paper on circumstellar dust, the author says, speaking of the emissivity/absorption of dust grains at visual and infrared wavelengths:
The dust shell model is consistent with the observed shape of the [IR] excess and the observed size of the ##60 \, \mu \text{m}## source, provided that ##(\varepsilon_\text{vis}/\varepsilon_\text{IR})## is near unity. Since ##\varepsilon_\text{vis}## for most material is near unity... it follows that ##\varepsilon_\text{IR}## also has to be near unity. This condition will normally be satisfied if the particle radius, ##a##, is comparable to or larger than ##\lambda_p / 2\pi##, where ##\lambda_p## is the wavelength of the peak emission.

My question is: where did the expression ##\lambda_p / 2\pi## come from, and what is the physical justification for it? I understand that small objects whose size is comparable to the wavelength of the incident light can't be resolved by that light, but what does that have to do with blackbody radiation and emissivity?
 
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  • #2
Read the latest Planck mission results. They have some good information on this.
 
  • #3
Planck Mission results seem vast...

Thanks, Chronos, for the reply.

I made my way to http://www.sciops.esa.int/index.php?project=PLANCK&page=Planck_Published_Papers, tried to find something specifically relating to my question, and failed, feeling overwhelmed by the sheer amount of their publications. I can see that the Planck Mission is obviously very concerned with dust and its properties, and I'm sure the answer is buried in there somewhere, but in the meantime, is there a specific paper, or webpage that you could send me a link for?
 
  • #4
I too could find nothing specifically relevant to your question. I took the liberty of doing some additional research and came up with this: Astrophysics of Dust in Cold Clouds, http://arxiv.org/abs/astro-ph/0304488. Hope that helps
 
  • #5
Thanks again, Chronos. The article is helpful, but will require more careful reading to find the answer I'm looking for. I feel as though there's something basic that I'm missing, but I can't quite put my finger on it.
I'll post again if I have any luck.
 

1) What is emissivity of dust grains?

Emissivity of dust grains is a measure of how efficiently they emit thermal radiation. It is a property that describes the ability of a dust grain to absorb and emit radiation, and is often expressed as a number between 0 and 1, with 1 being a perfect emitter.

2) How does the emissivity of dust grains affect their temperature?

The emissivity of dust grains plays a crucial role in determining their temperature. A higher emissivity means that the dust grains will absorb and emit more thermal radiation, leading to a higher temperature. On the other hand, a lower emissivity will result in lower temperatures.

3) What factors can influence the emissivity of dust grains?

The emissivity of dust grains can be influenced by various factors, including their size, shape, composition, and surface properties. For example, dust grains with rough surfaces tend to have higher emissivity compared to smooth grains.

4) How does the emissivity of dust grains impact their interactions with electromagnetic radiation?

The emissivity of dust grains affects their interactions with electromagnetic radiation in several ways. Higher emissivity allows dust grains to absorb and emit more radiation, making them visible to telescopes and other instruments that detect thermal radiation. It also affects the temperature of dust grains, which can impact their chemical and physical properties.

5) How do scientists measure the emissivity of dust grains?

There are various methods used to measure the emissivity of dust grains, including laboratory experiments and theoretical models. In laboratory experiments, scientists can use instruments like spectrometers to measure the amount of thermal radiation emitted by dust grains at different wavelengths. The data obtained from these experiments can then be used to calculate the emissivity. Theoretical models, on the other hand, use mathematical equations to estimate the emissivity based on the properties of dust grains.

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