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A-type star In the Harvard spectral classification system, a class of main-sequence star having spectra dominated by Balmer absorption lines of hydrogen. Stars of spectral class A are typically blue-white or white in color, measure between 1.4 and 2.1 times the mass of the Sun, and have surface temperatures of 7,600–10,000 kelvin.
Examples of star-forming regions are the Orion Nebula, the Rosette Nebula and the Omega Nebula. Feedback from star-formation, in the form of supernova explosions of massive stars, stellar winds or ultraviolet radiation from massive stars, or outflows from low-mass stars may disrupt the cloud, destroying the nebula after several million years.
The following is an incomplete list of known planetary nebulae. Image Name Messier Catalogue [a] NGC [a] Other designation [a] ... Eye of Sauron Nebula M 1-42: 10 14
Although these metals are present in stars in relatively tiny amounts, they have marked effects on stellar evolution and fusion reactions. When stars formed earlier in the universe they theoretically contained smaller quantities of heavier elements. [37] Known examples are the metal poor Population II stars.
NGC 6826 (also known as Caldwell 15) is a planetary nebula located in the constellation Cygnus. It is commonly referred to as the "Blinking Planetary", although many other nebulae exhibit such "blinking". When viewed through a small telescope, the brightness of the central star overwhelms the eye when viewed directly, obscuring the surrounding ...
The following articles contain lists of nebulae: List of dark nebulae; List of diffuse nebulae; List of planetary nebulae; List of protoplanetary nebulae;
Planetary nebulae, represented here by the Ring Nebula, are examples of emission nebulae. An emission nebula is a nebula formed of ionized gases that emit light of various wavelengths. The most common source of ionization is high-energy ultraviolet photons emitted from a nearby hot star .
This effect was observed for light from the Crab Nebula by Martin, Illing and Angel. [19] An optically thick circumstellar environment can potentially produce much larger CP than the interstellar medium. Martin [18] suggested that LP light can become CP near a star by multiple scattering in an optically thick asymmetric circumstellar dust cloud.