<i>HUBBLE SPACE TELESCOPE</i>NEAR-ULTRAVIOLET SPECTROSCOPY OF BRIGHT CEMP-<i>s</i>STARS

Placco, Vinicius M.; Ivans, Inese I.; Filler, Dan; Imig, Julie; Roederer, Ian U.; Abate, C.; Hansen, Terese T.; Cowan, J. J.; Frebel, Anna; Lawler, J. E.; Schatz, H.; Sneden, Christopher; Sobeck, Jennifer; Aoki, Wako; Smith, Verne V.; Bolte, Michael

doi:10.1088/0004-637x/812/2/109

Cited by 45 publications

(42 citation statements)

References 96 publications

(84 reference statements)

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“…It is clear that these two sub-classes of CEMP stars have different binary status, with implications for the nature of their progenitors. Figure 5 shows the distribution of A(C) as a function of [Fe/H], for CEMP stars with known (or likely, meaning that further confirmation is desired) binary status, including 35 CEMP-s/rs stars and 22 CEMP-no stars (Dearborn et al 1986;McClure & Woodsworth 1990;Preston & Sneden 2001;Thompson et al 2008;Spite et al 2013;Placco et al 2015;Hansen et al 2016b,c; Table 1. Although many CEMP stars do not yet have observational constraints on their binary nature, the information in hand does provide the basis for a number of interesting interpretations.…”

Section: Single Stars Vs Binary Starsmentioning

confidence: 99%

Observational Constraints on First-Star Nucleosynthesis. I. Evidence for Multiple Progenitors of Cemp-No Stars

Yoon

Beers

Placco

et al. 2016

ApJ

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185

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We investigate anew the distribution of absolute carbon abundance, A(C) = log (C), for carbonenhanced metal-poor (CEMP) stars in the halo of the Milky Way, based on high-resolution spectroscopic data for a total sample of 305 CEMP stars. The sample includes 147 CEMP-s (and CEMPr/s) stars, 127 CEMP-no stars, and 31 CEMP stars that are unclassified, based on the currently employed [Ba/Fe] criterion. We confirm previous claims that the distribution of A(C) for CEMP stars is (at least) bimodal, with newly determined peaks centered on A(C)= 7.96 (the high-C region) and A(C)= 6.28 (the low-C region). A very high fraction of CEMP-s (and CEMP-r/s) stars belong to the high-C region, while the great majority of CEMP-no stars reside in the low-C region. However, there exists complexity in the morphology of the A(C)-[Fe/H] space for the CEMP-no stars, a first indication that more than one class of first-generation stellar progenitors may be required to account for their observed abundances. The two groups of CEMP-no stars we identify exhibit clearly different locations in the A(Na)-A(C) and A(Mg)-A(C) spaces, also suggesting multiple progenitors. The clear distinction in A(C) between the CEMP-s (and CEMP-r/s) stars and the CEMP-no stars appears to be as successful, and likely more astrophysically fundamental, for the separation of these sub-classes as the previously recommended criterion based on [Ba/Fe] (and [Ba/Eu]) abundance ratios. This result opens the window for its application to present and future large-scale low-and medium-resolution spectroscopic surveys.

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Section: Single Stars Vs Binary Starsmentioning

confidence: 99%

Observational Constraints on First-Star Nucleosynthesis. I. Evidence for Multiple Progenitors of Cemp-No Stars

Yoon

Beers

Placco

et al. 2016

ApJ

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185

294

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“…Placco et al (2015) studied two bright CEMP-s stars with HST/STIS spectra, which allowed them to determine abundances for elements such as Ge, Nb, Mo, Lu, Pt, and Au. They also matched the abundance pattern with the latest models from Abate et al (2015a), which take into account not only the AGB evolution, but also the dynamics of the binary system.…”

Section: Nucleosynthesis Challengesmentioning

confidence: 99%

The role of binaries in the enrichment of the early Galactic halo

Hansen

Andersen

Nordström

et al. 2016

A&A

141

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Context. Detailed spectroscopic studies of metal-poor halo stars have highlighted the important role of carbon-enhanced metal-poor (CEMP) stars in understanding the early production and ejection of carbon in the Galaxy and in identifying the progenitors of the CEMP stars among the first stars formed after the Big Bang. Recent work has also classified the CEMP stars by absolute carbon abundance, A(C), into high-and low-C bands, mostly populated by binary and single stars, respectively. Aims. Our aim is to determine the frequency and orbital parameters of binary systems among the CEMP-s stars, which exhibit strong enhancements of neutron-capture elements associated with the s-process. This allows us to test whether local mass transfer from a binary companion is necessary and sufficient to explain their dramatic carbon excesses. Methods. We have systematically monitored the radial velocities of a sample of 22 CEMP-s stars for several years with ∼monthly, high-resolution, low S/N échelle spectra obtained at the Nordic Optical Telescope (NOT) at La Palma, Spain. From these spectra, radial velocities with an accuracy of ≈100 m s −1 were determined by cross-correlation with optimised templates. Results. Eighteen of the 22 stars exhibit clear orbital motion, yielding a binary frequency of 82 ± 10%, while four stars appear to be single (18 ± 10%). We thus confirm that the binary frequency of CEMP-s stars is much higher than for normal metal-poor giants, but not 100% as previously claimed. Secure orbits are determined for eleven of the binaries and provisional orbits for six long-period systems (P > 3000 days), and orbital circularisation timescales are discussed. Conclusions. The conventional scenario of local mass transfer from a former asymptotic giant branch (AGB) binary companion does appear to account for the chemical composition of most CEMP-s stars. However, the excess of C and s-process elements in some single CEMP-s stars was apparently transferred to their natal clouds by an external (distant) source. This finding has important implications for our understanding of carbon enrichment in the early Galactic halo and some high-redshift damped lyman alpha (DLA) systems, and of the mass loss from extremely metal-poor AGB stars.

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“…Uncertainties in the elemental abundance determinations, as well as the systematic uncertainties due to changes in the atmospheric parameters, were treated in the same way as described in Placco et al (2013Placco et al ( , 2015a. Table 5 shows how variations within the quoted uncertainties in each atmospheric parameter affect the derived chemical abundances.…”

Section: Uncertaintiesmentioning

confidence: 99%

OBSERVATIONAL CONSTRAINTS ON FIRST-STAR NUCLEOSYNTHESIS. II. SPECTROSCOPY OF AN ULTRA METAL-POOR CEMP-no STAR*

Placco

Frebel

Beers

et al. 2016

ApJ

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We report on the first high-resolution spectroscopic analysis of HE0020-1741, a bright (V=12.9), ultra metal-.7) star selected from the Hamburg/ESO Survey. This star exhibits low abundances of neutron-capture elements ([ ] Ba Fe = −1.1) and an absolute carbon abundance A (C)=6.1; based on either criterion, HE0020-1741 is subclassified as a carbon-enhanced metal-poor star without enhancements in neutron-capture elements (CEMP-no). We show that the light-element abundance pattern of HE0020-1741 is consistent with predicted yields from a massive), primordial-composition, supernova (SN) progenitor. We also compare the abundance patterns of other ultra metal-poor stars from the literature with available measures of C, N, Na, Mg, and Fe abundances with an extensive grid of SN models (covering the mass range - M 10 100), in order to probe the nature of their likely stellar progenitors. Our results suggest that at least two classes of progenitors are required at [ ] Fe H < -4.0, as the abundance patterns for more than half of the sample studied in this work (7 out of 12 stars) cannot be easily reproduced by the predicted yields.

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HUBBLE SPACE TELESCOPENEAR-ULTRAVIOLET SPECTROSCOPY OF BRIGHT CEMP-sSTARS

Cited by 45 publications

References 96 publications

Observational Constraints on First-Star Nucleosynthesis. I. Evidence for Multiple Progenitors of Cemp-No Stars

Observational Constraints on First-Star Nucleosynthesis. I. Evidence for Multiple Progenitors of Cemp-No Stars

The role of binaries in the enrichment of the early Galactic halo

OBSERVATIONAL CONSTRAINTS ON FIRST-STAR NUCLEOSYNTHESIS. II. SPECTROSCOPY OF AN ULTRA METAL-POOR CEMP-no STAR*

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