Of the convective envelope, T_b^dred, at the stage of the post-flash luminosity In this approach, the usualĬriterion (based on a constant minimum core mass for the occurrence ofĭredge-up, M_c^min) is replaced by one on the minimum temperature at the base Pulsing asymptotic giant branch (TP-AGB) stars.
Scheme for treating the third dredge-up in synthetic calculations of thermally Theoretical modelling is based on an improved As a result, lower-mass stars experience the first and third dredge-ups in their evolution but not the second.Download a PDF of the paper titled The third dredge-up and the carbon star luminosity functions in the Magellanic Clouds, by Paola Marigo (1 and 2) and 4 other authors Download PDF Abstract: We investigate the formation of carbon stars as a function of the stellar
The names of the dredge-ups are set by the evolutionary and structural state of the star in which each occurs, not by the sequence experienced by the star. The result is an increase in the abundance of carbon relative to oxygen, which can create a carbon star. This dredge-up causes helium, carbon and the s-process products to be brought to the surface. The third dredge-up occurs after a star enters the asymptotic giant branch and a flash occurs along a helium burning shell. This second dredge-up results in an increase in the surface abundance of 4He and 14N, whereas the amount of 12C and 16O decreases. When helium fusion comes to an end at the core, convection mixes the products of the CNO cycle. The second dredge-up occurs in stars with 4–8 solar masses. As a result of the convective mixing, the outer atmosphere will display the spectral signature of hydrogen fusion: the 12C/ 13C and C/N ratios are lowered, and the surface abundances of lithium and beryllium may be reduced. The first dredge-up occurs when a main-sequence star enters the red-giant branch. As a result, the fusion products are mixed into the outer layers of the stellar atmosphere where they can appear in the spectrum of the star. A dredge-up is a period in the evolution of a star where a surface convection zone extends down to the layers where material has undergone nuclear fusion.
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