Introduction to Stars: Spectra, Formation, Evolution, Collapse by Metin Bektas

Author:Metin Bektas [Bektas, Metin]
Language: eng
Format: azw3
Published: 2015-10-17T00:00:00+00:00

Image of the Cat's Eye Nebula, a bright planetary nebula located in the constellation Draco at a distance of roughly 1000 parsecs from Earth, first discovered in 1786 by William Herschel.

As the giant star sheds its envelope, the radius decreases while the surface temperature goes up, a logical consequence of exposing the hotter layers that were previously deep within the star to the outside world. The luminosity is roughly constant during the planetary nebulae stage, meaning that the variation of the radius R and surface temperature T must take place in a fashion that leaves the product L ~ R2 · T4 unchanged. In short: the changes must satisfy the proportionality R ~ T-2, so the doubling of the surface temperature is accompanied by the reduction of the radius to one-fourth of its initial value.

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