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| The '''source function''' is a characteristic of a stellar atmosphere, and in the case of no [[scattering]] of photons, describes the ratio of the emission coefficient to the absorption coefficient. It is a measure of how photons in a light beam are removed and replaced by new photons by the material it passes through. Its units in the cgs-system are erg s<sup>-1</sup> cm<sup>-2</sup> sr<sup>-1</sup> Hz<sup>-1</sup> and in SI are W m<sup>-2</sup> sr<sup>-1</sup> Hz<sup>-1</sup> . The ''source function'' can be written
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| :<math>S_{\lambda} \ \stackrel{\mathrm{def}}{=}\ \frac{j_{\lambda}}{\kappa_{\lambda}}</math>
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| where <math>j_{\lambda}</math> is the emission coefficient, <math>\kappa_{\lambda}</math> is the absorption coefficient (also known as the [[opacity (optics)|opacity]]). Putting this into the equation for [[radiative transfer]] we get
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| :<math>-\frac{1}{\kappa_{\lambda} \rho} \frac{dI_{\lambda}}{ds} = I_{\lambda} - S_{\lambda} </math> | |
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| where ''s'' is the distance measured along the path traveled by the beam. The minus sign on the left hand side shows that the intensity decreases as the beam travels, due to the absorption of photons.
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| ==See also== | |
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| * [[Radiative transfer]]
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| * [[Opacity (optics)]]
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| ==References==
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| * {{cite book
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| | author=B.W. Carrol, D.A. Ostlie
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| | title=An Introduction to Modern Astrophysics
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| | publisher=Addison-Wesley Publishing Company, Inc.
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| | year=1996
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| | isbn =0-321-21030-1 }}
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| [[Category:Astrophysics]]
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| [[Category:Stellar astronomy]]
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| {{star-stub}}
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Latest revision as of 20:15, 11 October 2014
Let me initial begin by introducing myself. My name is Boyd Butts even though it is not the title on my beginning certification. To collect cash is what her family members and her enjoy. California is our birth location. For many years I've been operating as a payroll clerk.
Here is my page; std testing at home