The Astrophysics of Emission-Line Stars by Tomokazu Kogure, Kam-Ching Leung

By Tomokazu Kogure, Kam-Ching Leung

Many forms of stars convey conspicuous emission strains of their optical spectra. those stars are widely known as emission line stars. Emission line stars are appealing to many folks due to their surprising phenomena and their variability. The Astrophysics of Emission Line Stars bargains normal details on emission line stars, ranging from a short creation to stellar astrophysics, after which relocating towards a extensive review of emission line stars together with early and overdue style stars in addition to pre-main series stars. particular references were ready in addition to an index for additional reading.

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44 Chapter 2. 1 Equations of radiative transfer Suppose a volume element with length ds and cross section da in a gas layer. The radiation passing through this volume perpendicularly to the surface do suffers some absorption and reduces its intensity. The absorbed energy dE A is supposed to be proportional to the intensity of radiation and. 1) where the constant K A (cm -1) is called the absorption coefficient. At the same time, the radiation intensity is increased by emission from this volume element.

26) In order to derive the temperature gradient, the flux must be integrated over the whole wavelength range. Since wavelength dependence of T A is not known, we again assume a gray atmosphere for simplicity. 27) where dTA is replaced by dr for the optical depth of total radiation. 24), then we get K == where C is an integration constant. 28) Chapter 2. Stellar Spectra and Radiation Fields 54 fA By definition, functions K, K A are the second moment of specific intensity (7A, 0) with respect to cos O.

And then to deduce the depth dependence of the source function for the atmospheric layer that the radiation at wavelength A is emitted. 2). (0,0) cosOd(cosO). 11). 12) for f>.. 14), we have 11" F>. (0) = 211" 1 1 (a>. + b>. ) cosO) cosOd(cosO) . 15) Chapter 2. 11), we get FA (0) =SA (TA =~). 16) This is the so-called Eddington-Barbier relation and shows that the flux coming out of the stellar surface equals the source function at the optical depth 7 A == 2/3. 11), this relation is useful for the understanding of the formation of stellar spectra.

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