Diferencies ente revisiones de «Estrella de carbonu»

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Iguo testu: -"períodu" +"periodu"
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m (Iguo testu: -"períodu" +"periodu")
El primeru d'ellos ye '''[[R Leporis|R leporis]]''', una estrella con calter y nome propiu, conocida tamién col románticu nome de “Estrella carmesí de Hind” (o, n'inglés, Crimson star) o'l macabru pero acertáu nome de “la gota de sangre”. El so alies dicir tou, y ye que cualesquier que mire esta estrella va entender que non tou nel cielu ye blancu y negru. Ye una estrella de carbonu, y como tal amuesa una increíble tonalidá acoloratada como poques podemos reparar pol nuesu telescopiu. ¿D'ónde vien esi color? L'atmósfera de R leporis tien más carbonu del habitual, proveniente de zones más internes de la estrella, tres la fusión de molécules d'heliu. El carbonu, según el monóxidu de carbonu, nun dexen pasar la lluz azul, colo cual la resultancia ye esa tonalidá acoloratada. Son estrelles desaxeradamente fríes, envalorándose para R leporis una temperatura superficial pocu mayor de 2.000º K, con un diámetru que supera unes 500 vegaes al nuesu sol. Les estrelles de carbonu son de tipu espectral C y van camín de convertise nuna nana blanca, cola so envoltura formando una nebulosa planetaria.
 
Pero R leporis ye, amás, una estrella variable tipu Mira. Siendo'l prototipu Mira Ceti, que vamos ver n'otra ocasión, son estrelles que'l so rellumu presenta grandes variaciones tocantes a magnitú mientres un períoduperiodu mayor de 100 díes. De color coloráu intensu, les variables tipu Mira son xigantes coloraes d'edá avanzada que s'espanden y contraen sufriendo con ello cambeos na temperatura y lluminosidá, esprendiéndose adulces de la so envoltura gaseosa. Ello ye que munches d'estes estrelles nun tienen forma esférica y van dexando un rastru de gases tres de sigo. Na siguiente imaxe podemos apreciar, en lluz ultravioleta, los restos que va soltando Mira Ceti, como si d'una cometa estelar tratárase, anque a xulgar pola semeya más bien paeciera una aguamala espacial<!--
The '''non-classical''' kinds of carbon stars are believed to be [[binary star]]s, where one star is observed to be a giant star (or occasionally a [[rede dwarf]]) and the other a [[white dwarf]]. The star presently observed to be a giant star accreted carbon-rich material when it was still a [[main sequence]] star from its companion (that is, the star that is now the white dwarf) when the latter was still a classical carbon star. That phase of [[stellar evolution]] is relatively brief, and most such stars ultimately end up as white dwarfs. We are now seeing these systems a comparatively long time after the [[mass transfer]] event, so the extra carbon observed in the present rede giant was not produced within that star.<ref>R. McClure, Journal of the Royals Astronomical Society of Canada, vol 79, pp. 277-293, Dec. 1985</ref> This scenario is also accepted as the origin of the [[barium stars]], which are also characterized as having strong spectral features of carbon molecules and of barium (an [[s-process element]]). Sometimes the stars whose excess carbon came from this mass transfer are called "extrinsic" carbon stars to distinguish them from the "intrinsic" AGB stars which produz the carbon internally. Many of these extrinsic carbon stars are not luminous or cool enough to have made their own carbon, which was a puzzle until their binary nature was discovered.
 
Other less convincing mechanisms, such as [[CNO cycle]] unbalancing and [[Core Helium Flax]] have also been proposed as mechanisms for carbon enrichment in the atmospheres of smaller carbon stars.