![F dredge up](https://cdn1.cdnme.se/5447227/9-3/14_64e61dfbddf2b36505b4c7c8.png)
The third dredge-up brings helium, carbon, and the s-process products to the surface, increasing the abundance of carbon relative to oxygen in some larger stars this is the process that turns the star into a carbon star. The third dredge-up The third dredge-up occurs after a star enters the asymptotic giant branch, after a flash occurs in a helium-burning shell.This second dredge-up causes an increase in the surface abundance of 4He and 14N, whereas the amount of 12C and 16O decreases.
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When helium fusion comes to an end at the core, convection mixes the products of the CNO cycle. The second dredge-up 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 The first dredge-up occurs when a main-sequence star enters the red-giant branch.Consequently, the fusion products are mixed into the outer layers of the star's atmosphere, where they can be seen in stellar spectra.
![f dredge up f dredge up](https://www.nidec-industrial.com/wp-content/uploads/2017/07/dredges2-768x576.jpg)
By definition, during a dredge-up, a convection zone extends all the way from the star's surface down to the layers of material that have undergone fusion.
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A dredge-up is any one of several stages in the evolution of some stars.
![F dredge up](https://cdn1.cdnme.se/5447227/9-3/14_64e61dfbddf2b36505b4c7c8.png)