Matrozis, E., Abate, C. and Stancliffe, R. J. (2017). How much mass and angular momentum can the progenitors of carbon-enriched stars accrete? Astron. Astrophys., 606. LES ULIS CEDEX A: EDP SCIENCES S A. ISSN 1432-0746

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Abstract

The chemically peculiar barium stars, CH stars, and most carbon-enhanced metal-poor (CEMP) stars are all believed to be the products of mass transfer in binary systems from a now extinct asymptotic giant branch (AGB) primary star. The mass of the AGB star and the orbital parameters of the system are the key factors usually considered when determining how much mass is transferred onto the lower-mass main-sequence companion. What is usually neglected, however, is the angular momentum of the accreted material, which should spin up the accreting star. If the star reaches critical rotation, further accretion should cease until the excess angular momentum is somehow dealt with. If the star cannot redistribute or lose the angular momentum while the primary is on the AGB, the amount of mass accreted could be much lower than otherwise expected. Here we present calculations, based on detailed stellar evolution models, of the mass that can be accreted by putative progenitors of Ba and CEMP stars before they reach critical rotation under the assumption that no angular momentum loss occurs during the mass transfer. We consider different accretion rates and values of specific angular momentum. The most stringent limits on the accreted masses result from considering accretion from a Keplerian accretion disk, which is likely present during the formation of most extrinsically-polluted carbon-enriched stars. Our calculations indicate that in this scenario only about 0.05 M-circle dot of material can be added to the accreting star before it reaches critical rotation, which is much too low to explain the chemical enrichment of many Ba and CEMP stars. Either the specific angular momentum of the accreted material has to effectively be lower by about a factor of ten than the Keplerian value, or significant angular momentum losses must occur for substantial accretion to take place.

Item Type: Journal Article
Creators:
CreatorsEmailORCIDORCID Put Code
Matrozis, E.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Abate, C.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Stancliffe, R. J.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
URN: urn:nbn:de:hbz:38-213975
DOI: 10.1051/0004-6361/201730746
Journal or Publication Title: Astron. Astrophys.
Volume: 606
Date: 2017
Publisher: EDP SCIENCES S A
Place of Publication: LES ULIS CEDEX A
ISSN: 1432-0746
Language: English
Faculty: Unspecified
Divisions: Unspecified
Subjects: no entry
Uncontrolled Keywords:
KeywordsLanguage
ASYMPTOTIC GIANT BRANCH; METAL-POOR STARS; CLOSE BINARY-SYSTEMS; CH-STARS; STELLAR EVOLUTION; ROTATING STARS; TIDAL TORQUES; PLANETARY-NEBULA; WIND ACCRETION; BARIUMMultiple languages
Astronomy & AstrophysicsMultiple languages
Refereed: Yes
URI: http://kups.ub.uni-koeln.de/id/eprint/21397

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