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Abstract: The carbon-enhanced metal-poor CEMP stars constitute approximately onefifth of the metal-poor Fe-H ~< -2 population but their origin is not wellunderstood. The most widely accepted formation scenario, invokes mass-transferof carbon-rich material from a thermally-pulsing asymptotic giant branchTPAGB primary star to a less massive main-sequence companion which is seentoday. Recent studies explore the possibility that an initial mass functionbiased toward intermediate-mass stars is required to reproduce the observedCEMP fraction in stars with metallicity Fe-H < -2.5. These models alsoimplicitly predict a large number of nitrogen-enhanced metal-poor NEMP starswhich is not seen. We investigate whether the observed CEMP and NEMP toextremely metal-poor EMP ratios can be explained without invoking a change inthe initial mass function.We confirm earlier findings that with current detailed TPAGB models the largeobserved CEMP fraction cannot be accounted for. We find that efficient thirddredge up in low-mass less than 1.25Msun, low-metallicity stars may offer atleast a partial explanation to the large observed CEMP fraction while remainingconsistent with the small observed NEMP fraction.



Autor: Robert G. Izzard 1,2, Evert Glebbeek 1,3, Richard J. Stancliffe 4,5, Onno Pols 1 1 Sterrenkundig Instituut, Universiteit Utrecht

Fuente: https://arxiv.org/







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