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Questions tagged [radiative-transfer]

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Eddington-Barbier approximation next term for flux

When adding a term to E-B approx it should lead to this for the astronomical flux. $\frac{F}{\pi }\approx S\left(\tau =\frac{2}{3}\right)+\frac{5}{18}\frac{d^2S}{d\tau ^2}_{\tau =\frac{2}{3}}$ S is ...
user54705's user avatar
1 vote
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77 views

Has anybody measured the mass density profile $\Sigma = \Sigma (r)$ of a protoplanetary disk? (when $r<1$ AU)

I've been trying to find research articles where the mass density distribution $\mathrm{\Sigma = \Sigma(r)}$ is determined for protoplanetary disks, when $r<1$ au. For instance: Here A. Miotello, ...
nuwe's user avatar
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3 votes
1 answer
466 views

How are absorption cross sections calculated?

I would like to develop a more intuitive understanding of cross sections, in the context of radiative transfer. I understand that a cross section, $\sigma_\nu$, is a measure of a given atom/molecule's ...
lucas's user avatar
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1 vote
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Evaluating Intensity ratio $I(0,\mu)/I(0,1)$ in non-isotropic region

We are given a problem: Consider a grey atmosphere in radiative equilibrium. If the total pressure ($P$) and energy density ($u$) are related by $$P=\frac{u}{\tau^2}$$ in a non-isotropic region, ...
Young Kindaichi's user avatar
1 vote
0 answers
259 views

A good definition of specific intensity?

I’m studying specific intensity for a course on astronomical instrumentation. I can’t quite get my head around the proper definition of the term. One definition I’ve found in various lecture notes / ...
Heatherfield's user avatar
3 votes
1 answer
267 views

Scattered Intensity of Light vs Angles of Incidence and Emission

So I just derived an expression for the scattered intensity of light from an atmosphere with ideal isotopic scattering: $I/F=\frac{cos(i)}{4(cos(e)+cos(i))}$, where $I$ is intensity, $F$ is flux, $i$ ...
Spuds's user avatar
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3 votes
1 answer
1k views

What is main radiative mechanism in Gunn-Peterson effect?

I'm having a hard time understanding the Gunn-Peterson effect and the Ly-alpha line and I've written a couple of questions below. The trough we see in the spectra of quasars is the Gunn-Peterson ...
user9404237's user avatar
2 votes
1 answer
193 views

Determining line ratios in planetary nebula

I know that the line strength ratio tells us how hot the electron plasma in a nebula is, and also give information about the electron densities in the nebula. But how do you compute the line ratios? ...
user9404237's user avatar
0 votes
1 answer
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Relation between intensity of Sun and the light that is emitted from surface of sun [closed]

please correct me if I am mistaken, I was in the middle of a thought process. We take a unit area dA of sun,, which is emitting light directly to our line of sight. But there are also numerous other ...
bhjghjh's user avatar
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1 answer
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Meaning of critical density in radiative transfer

I do not understand completely the meaning of critical density when talking about atomic or molecular line emission in astrophysical gas clouds: I know that it is way more complex than this, but just ...
Federico Esposito's user avatar
4 votes
1 answer
676 views

Why Free-Free emission is regarded as Thermal emission?

I read that thermal emission/radiation are the ones whose spectra is similar to that of a Black body radiation. Also thermal radiation depends solely on the temperature of the object. How can we ...
Rian's user avatar
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6 votes
0 answers
481 views

Linear limb darkening coefficient, u

I was wondering if anyone knew of any resources to understand the linear limb darkening coefficient, $u$. That is to say, how the $\theta$-dependent coefficient $u$ (or sometimes $b_{\nu}$) varies ...
MichaelJRoberts's user avatar
2 votes
2 answers
969 views

What is space temperature around Earth?

What is the equilibrium temperature that a black body will reach at the Earth's distance from Sun?
Anixx's user avatar
  • 1,265
13 votes
2 answers
7k views

How does one determine the effective temperature of a star from its spectrum?

Determining effective temperature of a star is in general a non-trivial task. Simple reason for this is that we can only study the electromagnetic radiation from a star, but not the temperature ...
Alexey Bobrick's user avatar
8 votes
2 answers
625 views

How well can we in principle determine $T_{\textrm{eff}}$ of a star?

This is a question about the basics of astronomy, which I have never happened to see a good discussion for. It is about how well would we be able to measure effective temperature of a star, if we had ...
Alexey Bobrick's user avatar