TOPoS II. On the bimodality of carbon abundance in CEMP stars Implications on the early chemical evolution of galaxies

Bonifacio, P., Caffau, E., Spite, M., Limongi, M., Chieffi, A., Klessen, R. S., Francois, P., Molaro, P., Ludwig, H. -G., Zaggia, S., Spite, F., Plez, B., Cayrel, R., Christlieb, N., Clark, Paul ORCID: https://orcid.org/0000-0002-4834-043X, Glover, S. C. O., Hammer, F., Koch, A., Monaco, L., Sbordone, L. and Steffen, M. 2015. TOPoS II. On the bimodality of carbon abundance in CEMP stars Implications on the early chemical evolution of galaxies. Astronomy and Astrophysics 579 , A28. 10.1051/0004-6361/201425266

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Abstract

In the course of the TOPoS (Turn Off Primordial Stars) survey, aimed at discovering the lowest metallicity stars, we have found several carbon-enhanced metal-poor (CEMP) stars. We here present our analysis of six CEMP stars. Calcium and carbon are the only elements that can be measured in all six stars. The range is -5.0<=[Ca/H]< -2.1 and 7.12<=A(C)<=8.65. For star SDSS J1742+2531 we were able to detect three FeI lines from which we deduced [Fe/H]=-4.80, from four CaII lines we derived [Ca/H]=-4.56, and from synthesis of the G-band we derived A(C)=7.26. For SDSS J1035+0641 we were not able to detect any iron lines, yet we could place a robust (3sigma) upper limit of [Fe/H]< -5.0 and measure the Ca abundance, with [Ca/H]=-5.0, and carbon, A(C)=6.90. No lithium is detected in the spectrum of SDSS J1742+2531 or SDSS J1035+0641, which implies a robust upper limit of A(Li)<1.8 for both stars. Our measured carbon abundances confirm the bimodal distribution of carbon in CEMP stars, identifying a high-carbon band and a low-carbon band. We propose an interpretation of this bimodality according to which the stars on the high-carbon band are the result of mass transfer from an AGB companion, while the stars on the low-carbon band are genuine fossil records of a gas cloud that has also been enriched by a faint supernova (SN) providing carbon and the lighter elements. (Abridged)

Item Type:	Article
Date Type:	Publication
Status:	Published
Schools:	Physics and Astronomy
Subjects:	Q Science > QB Astronomy
Publisher:	EDP Sciences
ISSN:	0004-6361
Date of First Compliant Deposit:	20 June 2017
Date of Acceptance:	10 April 2015
Last Modified:	08 May 2023 02:28
URI:	https://orca.cardiff.ac.uk/id/eprint/89599

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