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TOPoS: on the bimodality of carbon abundance in CEMP stars Implications on the early chemical evolution of galaxies

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TOPoS: on the bimodality of carbon abundance in CEMP stars Implications on the early chemical evolution of galaxies. / Bonifacio, P.; Caffau, E.; Spite, M. et al.
In: Astronomy and Astrophysics, Vol. 579, A28, 07.2015.

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Harvard

Bonifacio, P, Caffau, E, Spite, M, Limongi, M, Chieffi, A, Klessen, RS, Francois, P, Molaro, P, Ludwig, H-G, Zaggia, S, Spite, F, Plez, B, Cayrel, R, Christlieb, N, Clark, PC, Glover, SCO, Hammer, F, Koch, A, Monaco, L, Sbordone, L & Steffen, M 2015, 'TOPoS: on the bimodality of carbon abundance in CEMP stars Implications on the early chemical evolution of galaxies', Astronomy and Astrophysics, vol. 579, A28. https://doi.org/10.1051/0004-6361/201425266

APA

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, P. C., Glover, S. C. O., Hammer, F., Koch, A., Monaco, L., ... Steffen, M. (2015). TOPoS: on the bimodality of carbon abundance in CEMP stars Implications on the early chemical evolution of galaxies. Astronomy and Astrophysics, 579, Article A28. https://doi.org/10.1051/0004-6361/201425266

Vancouver

Bonifacio P, Caffau E, Spite M, Limongi M, Chieffi A, Klessen RS et al. TOPoS: on the bimodality of carbon abundance in CEMP stars Implications on the early chemical evolution of galaxies. Astronomy and Astrophysics. 2015 Jul;579:A28. Epub 2015 Jun 22. doi: 10.1051/0004-6361/201425266

Author

Bonifacio, P. ; Caffau, E. ; Spite, M. et al. / TOPoS : on the bimodality of carbon abundance in CEMP stars Implications on the early chemical evolution of galaxies. In: Astronomy and Astrophysics. 2015 ; Vol. 579.

Bibtex

@article{0449d99251954c24a00869c69683c11d,
title = "TOPoS: on the bimodality of carbon abundance in CEMP stars Implications on the early chemical evolution of galaxies",
abstract = "Context. In the course of the Turn Off Primordial Stars (TOPoS) survey, aimed at discovering the lowest metallicity stars, we have found several carbon-enhanced metal-poor (CEMP) stars. These stars are very common among the stars of extremely low metallicity and provide important clues to the star formation processes. We here present our analysis of six CEMP stars. Aims. We want to provide the most complete chemical inventory for these six stars in order to constrain the nucleosynthesis processes responsible for the abundance patterns. Methods. We analyse both X-Shooter and UVES spectra acquired at the VLT. We used a traditional abundance analysis based on OSMARCS 1D local thermodynamic equilibrium (LTE) model atmospheres and the turbospectrum line formation code. Results. 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 Fe i lines from which we deduced [Fe/H] = −4.80, from four Ca ii 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 (3σ) upper limit of [Fe/H] < −5.0 and measure the Ca abundance, with [Ca/H] = −5.0, and carbon, A(C) = 6.90, suggesting that this star could be even more metal-poor than SDSS J1742+2531. This makes these two stars the seventh and eighth stars known so far with [Fe/H] < −4.5, usually termed ultra-iron-poor (UIP) stars. 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. Conclusions. 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. The abundance pattern of the UIP stars shows a large star-to-star scatter in the [X/Ca] ratios for all elements up to aluminium (up to 1 dex), but this scatter drops for heavier elements and is at most of the order of a factor of two. We propose that this can be explained if these stars are formed from gas that has been chemically enriched by several SNe, that produce the roughly constant [X/Ca] ratios for the heavier elements, and in some cases the gas has also been polluted by the ejecta of a faint SN that contributes the lighter elements in variable amounts. The absence of lithium in four of the five known unevolved UIP stars can be explained by a dominant role of fragmentation in the formation of these stars. This would result either in a destruction of lithium in the pre-main-sequence phase, through rotational mixing or to a lack of late accretion from a reservoir of fresh gas. The phenomenon should have varying degrees of efficiency.",
keywords = "stars: Population II , stars: abundances, stars: Population III, Galaxy: abundances, Galaxy: formation , Galaxy: halo",
author = "P. Bonifacio and E. Caffau and M. Spite and M. Limongi and A. Chieffi and Klessen, {R. S.} and P. Francois and P. Molaro and H.-G. Ludwig and S. Zaggia and F. Spite and B. Plez and R. Cayrel and N. Christlieb and Clark, {P. C.} and Glover, {S. C. O.} and F. Hammer and Andreas Koch and L. Monaco and L. Sbordone and M. Steffen",
year = "2015",
month = jul,
doi = "10.1051/0004-6361/201425266",
language = "English",
volume = "579",
journal = "Astronomy and Astrophysics",
issn = "1432-0746",
publisher = "EDP Sciences",

}

RIS

TY - JOUR

T1 - TOPoS

T2 - on the bimodality of carbon abundance in CEMP stars Implications on the early chemical evolution of galaxies

AU - Bonifacio, P.

AU - Caffau, E.

AU - Spite, M.

AU - Limongi, M.

AU - Chieffi, A.

AU - Klessen, R. S.

AU - Francois, P.

AU - Molaro, P.

AU - Ludwig, H.-G.

AU - Zaggia, S.

AU - Spite, F.

AU - Plez, B.

AU - Cayrel, R.

AU - Christlieb, N.

AU - Clark, P. C.

AU - Glover, S. C. O.

AU - Hammer, F.

AU - Koch, Andreas

AU - Monaco, L.

AU - Sbordone, L.

AU - Steffen, M.

PY - 2015/7

Y1 - 2015/7

N2 - Context. In the course of the Turn Off Primordial Stars (TOPoS) survey, aimed at discovering the lowest metallicity stars, we have found several carbon-enhanced metal-poor (CEMP) stars. These stars are very common among the stars of extremely low metallicity and provide important clues to the star formation processes. We here present our analysis of six CEMP stars. Aims. We want to provide the most complete chemical inventory for these six stars in order to constrain the nucleosynthesis processes responsible for the abundance patterns. Methods. We analyse both X-Shooter and UVES spectra acquired at the VLT. We used a traditional abundance analysis based on OSMARCS 1D local thermodynamic equilibrium (LTE) model atmospheres and the turbospectrum line formation code. Results. 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 Fe i lines from which we deduced [Fe/H] = −4.80, from four Ca ii 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 (3σ) upper limit of [Fe/H] < −5.0 and measure the Ca abundance, with [Ca/H] = −5.0, and carbon, A(C) = 6.90, suggesting that this star could be even more metal-poor than SDSS J1742+2531. This makes these two stars the seventh and eighth stars known so far with [Fe/H] < −4.5, usually termed ultra-iron-poor (UIP) stars. 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. Conclusions. 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. The abundance pattern of the UIP stars shows a large star-to-star scatter in the [X/Ca] ratios for all elements up to aluminium (up to 1 dex), but this scatter drops for heavier elements and is at most of the order of a factor of two. We propose that this can be explained if these stars are formed from gas that has been chemically enriched by several SNe, that produce the roughly constant [X/Ca] ratios for the heavier elements, and in some cases the gas has also been polluted by the ejecta of a faint SN that contributes the lighter elements in variable amounts. The absence of lithium in four of the five known unevolved UIP stars can be explained by a dominant role of fragmentation in the formation of these stars. This would result either in a destruction of lithium in the pre-main-sequence phase, through rotational mixing or to a lack of late accretion from a reservoir of fresh gas. The phenomenon should have varying degrees of efficiency.

AB - Context. In the course of the Turn Off Primordial Stars (TOPoS) survey, aimed at discovering the lowest metallicity stars, we have found several carbon-enhanced metal-poor (CEMP) stars. These stars are very common among the stars of extremely low metallicity and provide important clues to the star formation processes. We here present our analysis of six CEMP stars. Aims. We want to provide the most complete chemical inventory for these six stars in order to constrain the nucleosynthesis processes responsible for the abundance patterns. Methods. We analyse both X-Shooter and UVES spectra acquired at the VLT. We used a traditional abundance analysis based on OSMARCS 1D local thermodynamic equilibrium (LTE) model atmospheres and the turbospectrum line formation code. Results. 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 Fe i lines from which we deduced [Fe/H] = −4.80, from four Ca ii 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 (3σ) upper limit of [Fe/H] < −5.0 and measure the Ca abundance, with [Ca/H] = −5.0, and carbon, A(C) = 6.90, suggesting that this star could be even more metal-poor than SDSS J1742+2531. This makes these two stars the seventh and eighth stars known so far with [Fe/H] < −4.5, usually termed ultra-iron-poor (UIP) stars. 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. Conclusions. 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. The abundance pattern of the UIP stars shows a large star-to-star scatter in the [X/Ca] ratios for all elements up to aluminium (up to 1 dex), but this scatter drops for heavier elements and is at most of the order of a factor of two. We propose that this can be explained if these stars are formed from gas that has been chemically enriched by several SNe, that produce the roughly constant [X/Ca] ratios for the heavier elements, and in some cases the gas has also been polluted by the ejecta of a faint SN that contributes the lighter elements in variable amounts. The absence of lithium in four of the five known unevolved UIP stars can be explained by a dominant role of fragmentation in the formation of these stars. This would result either in a destruction of lithium in the pre-main-sequence phase, through rotational mixing or to a lack of late accretion from a reservoir of fresh gas. The phenomenon should have varying degrees of efficiency.

KW - stars: Population II

KW - stars: abundances

KW - stars: Population III

KW - Galaxy: abundances

KW - Galaxy: formation

KW - Galaxy: halo

U2 - 10.1051/0004-6361/201425266

DO - 10.1051/0004-6361/201425266

M3 - Journal article

VL - 579

JO - Astronomy and Astrophysics

JF - Astronomy and Astrophysics

SN - 1432-0746

M1 - A28

ER -