Wind Roche-lobe overflow: Application to carbon-enhanced metal-poor stars

By C. Abate, O. Pols, Robert G. Izzard, S. Mohamed, Selma de Mink. 2013

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Carbon-enhanced metal-poor stars (CEMP) are observed as a substantial fraction of the very metal-poor stars in the Galactic halo. Most CEMP stars are also enriched in s-process elements and these are often found in binary systems. This suggests that the carbon enrichment is due to mass transfer in the past from an asymptotic giant branch (AGB) star on to a low-mass companion. Models of binary population synthesis are not able to reproduce the observed fraction of CEMP stars without invoking non-standard nucleosynthesis or a substantial change in the initial mass function. This is interpreted as evidence of missing physical ingredients in the models. Recent hydrodynamical simulations show that e cient wind mass transfer is possible in the case of the slow and dense winds typical of AGB stars through a mechanism called wind Roche-lobe overflow (WRLOF), which lies in between the canonical Bondi-Hoyle-Lyttleton (BHL) accretion and Roche-lobe overflow. WRLOF has an e ect on the accretion e ciency of mass transfer and on the angular momentum lost by the binary system. The aim of this work is to understand the overall e ect of WRLOF on the population of CEMP stars. To simulate populations of low-metallicity binaries we combined a synthetic nucleosynthesis model with a binary population synthesis code. In this code we implemented the WRLOF mechanism. We used the results of hydrodynamical simulations to model the e ect of WRLOF on the accretion e ciency and we took the e ect on the angular momentum loss into account by assuming a simple prescription. The combination of these two e ects widens the range of systems that become CEMP stars towards longer initial orbital periods and lower mass secondary stars. As a consequence the number of CEMP stars predicted by our model increases by a factor 1:2 1:8 compared to earlier results that consider the BHL prescription. Moreover, higher enrichments of carbon are produced and the final orbital period distribution is shifted towards shorter periods.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/db994ae2d66b8820e1fc7716f8551e276ecbf58e

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Citations in the corpus

Binarity in carbon-enhanced metal-poor stars (2014, background): “As shown in Abate et al. (2013), various unknowns in the exact parameters of the mass transfer will lead to different final orbits, due to angular momentum loss in the process.”
CARBON-ENHANCED METAL-POOR STARS IN SDSS/SEGUE. I. CARBON ABUNDANCE ESTIMATION AND FREQUENCY OF CEMP STARS (2013, methodology): “However, Izzard et al. (2009) and Abate et al. (2013), using a binary population model alone, could not reproduce the high fraction of CEMP stars among the most metal-poor stars.”
Dawes Review 6: The Impact of Companions on Stellar Evolution (2016, background): “The properties of these systems allow direct tests of uncertain physical processes such as wind accretion efficiency, wind Roche-lobe overflow (Abate et al., 2013), mixing in the accreting star (e.g. thermohaline mixing; Stancliffe et al. 2013) and nucleosynthesis in stars that died many billions…”
Mass loss of stars on the asymptotic giant branch (2018, background): “, the origin of carbon-enhanced metal-poor stars (Abate et al. 2013).”
Chemical tagging with APOGEE: Discovery of a large population of N-rich stars in the inner Galaxy (2016, background): “…takes place effectively, which is highly uncertain, due to the current incomplete understanding of mass transfer during the common envelope phase and the treatment of angular momentum loss (for a discussion of the theory and examples of its applications, see Abate et al. 2013, 2015, respectively).”