Exploring the Origin of Lithium, Carbon, Strontium, and Barium With Four New Ultra Metal-Poor Stars

Hansen, T. T.; Hansen, C. J.; Christlieb, N.; Yong, David; Bessell, M. S.; Pérez, Ana E. García; Beers, Timothy C.; Placco, Vinicius M.; Frebel, Anna; Norris, John E.; Asplund, Martin

doi:10.1088/0004-637x/787/2/162

Cited by 92 publications

(108 citation statements)

References 91 publications

Supporting

Mentioning

102

Contrasting

Order By: Relevance

“…There are now five known unevolved stars with iron abundance below −4.5: HE 1327-2326 (Frebel et al 2005), SDSS J1029+1729 , HE 0233-0343 (Hansen et al 2014), SDSS J1742+2531 (Caffau et al 2013a and this paper) and SDSS J1035+0641 (this paper). SDSS J1742+2531 and SDSS J1035+0641 have no measurable lithium, like HE 1327-2326 and SDSS J1029+1729, at variance with most of the stars found at higher iron abundance with similar atmospheric parameters.…”

Section: Lithiummentioning

confidence: 78%

“…10. HE 0233-0343 is very similar to SDSS J1742+2531 both for atmospheric parameters and chemical abundances of C, Ca, and Fe, but it has a detectable lithium doublet that implies A(Li) = 1.77 (Hansen et al 2014), thus roughly a factor of three below the Spite plateau.…”

Section: Lithiummentioning

confidence: 86%

“…We selected from the literature the following sample of stars with [Fe/H] < −3.5: HE 0107-5240 (Christlieb et al 2004); HE 1327-2326 (Frebel et al 2008); HE 0557-4840 (Norris et al 2007); HE 0134-1519, HE 0233-0343, HE 1310-0536 (Hansen et al 2014); SMSS J0313-6708 (Keller et al 2014); CS 22949-037 (Depagne et al 2002;Norris et al 2002);and G 77-61 (Plez & Cohen 2005;). In addition, as an example of a carbon-normal star, we consider the most metal-poor star known to date, SDSS J1029+1729 .…”

Section: On the Chemical Composition And Star Formationmentioning

confidence: 99%

See 2 more Smart Citations

TOPoS

Bonifacio

Caffau

Spite

et al. 2015

A&A

Self Cite

170

232

View full text Add to dashboard Cite

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. 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 Article published by EDP Sciences A28, page 1 of 20 A&A 579, A28 (2015) 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.

show abstract

Section: Lithiummentioning

confidence: 78%

Section: Lithiummentioning

confidence: 86%

Section: On the Chemical Composition And Star Formationmentioning

confidence: 99%

See 1 more Smart Citation

TOPoS

Bonifacio

Caffau

Spite

et al. 2015

A&A

Self Cite

170

232

View full text Add to dashboard Cite

show abstract

“…At [Fe/H] = −2.52 and [C/Fe] = 1.44 dex, the latter provides a typical example of a carbon-enhanced metal-poor (CEMP) star (Beers & Christlieb 2005). The origin of its carbon over-abundance is most likely the mass transfer from the envelope of an asymptotic giant branch (AGB) star binary companion (now a white dwarf; e.g., Aoki et al 2007;Sneden et al 2008;Hansen et al 2014), consistent with the observed very strong enrichment of s-process elements (Sect. 4.6).…”

Section: Light Elements: C Li Namentioning

confidence: 99%

Metal-poor stars towards the Galactic bulge: A population potpourri

Koch

McWilliam

Preston

et al. 2016

A&A

View full text Add to dashboard Cite

We present a comprehensive chemical abundance analysis of five red giants and two horizontal branch (HB) stars towards the southern edge of the Galactic bulge, at (l, b) ∼ (0 • ,−11 • ). Based on high-resolution spectroscopy obtained with the Magellan/MIKE spectrograph, we derived up to 23 chemical element abundances and identify a mixed bag of stars, representing various populations in the central regions of the Galaxy. Although cosmological simulations predict that the inner Galaxy was host to the first stars in the Universe, we see no chemical evidence of the ensuing massive supernova explosions: all of our targets exhibit halo-like, solar [Sc/Fe] ratios, which is in contrast to the low values predicted from Population III nucleosynthesis. One of the targets is a CEMP-s star at [Fe/H] = −2.52 dex, and another target is a moderately metal-poor ([Fe/H] = −1.53 dex) CH star with strong enrichment in s-process elements (e.g., [Ba/Fe] = 1.35). These individuals provide the first contenders of these classes of stars towards the bulge. Four of the carbon-normal stars exhibit abundance patterns reminiscent of halo star across a metallicity range spanning −2.0 to −2.6 dex, i.e., enhanced α-elements and solar Fe-peak and neutron-capture elements, and the remaining one is a regular metal-rich bulge giant. The position, distance, and radial velocity of one of the metal-poor HB stars coincides with simulations of the old trailing arm of the disrupted Sagittarius dwarf galaxy. While their highly uncertain proper motions prohibit a clear kinematic separation, the stars' chemical abundances and distances suggest that these metal-poor candidates, albeit located towards the bulge, are not of the bulge, but rather inner halo stars on orbits that make them pass through the central regions. Thus, we caution similar claims of detections of metal-poor stars as true habitants of the bulge.

show abstract

“…with [Fe H] 7.1 < − , has already been reported (Keller et al 2014). The addition of this star raises the number of stars known to have [Fe H] 4.5 ⩽ − to six (Christlieb et al 2002;Frebel et al 2005;Norris et al 2007;Caffau et al 2011;Hansen et al 2014b;Keller et al 2014), and the SkyMapper EMP star candidate selection technique shows the promise of finding more of these stars. A corresponding survey for the most metal-poor and oldest stars in the Galactic bulge using SkyMapper photometry and AAOmega/ AAT multi-object spectroscopy is also underway (PI M. Asplund; see Howes et al 2014 for first results).…”

Section: Introductionmentioning

confidence: 99%

High-Resolution Spectroscopic Study of Extremely Metal-Poor Star Candidates From the Skymapper Survey

Jacobson

Keller

Frebel

et al. 2015

ApJ

Self Cite

125

145

View full text Add to dashboard Cite

The SkyMapper Southern Sky Survey is carrying out a search for the most metal-poor stars in the Galaxy. It identifies candidates by way of its unique filter set which allows for estimation of stellar atmospheric parameters. The set includes a narrow filter centered on the Ca II K 3933 Å line, enabling a robust estimate of stellar metallicity. Promising candidates are then confirmed with spectroscopy. We present the analysis of Magellan Inamori Kyocera Echelle high-resolution spectroscopy of 122 metal-poor stars found by SkyMapper in the first two years of commissioning observations. Forty-one stars have These results demonstrate the ability to identify extremely metal-poor stars from SkyMapper photometry, pointing to increased sample sizes and a better characterization of the metal-poor tail of the halo metallicity distribution function in the future.

show abstract

Exploring the Origin of Lithium, Carbon, Strontium, and Barium With Four New Ultra Metal-Poor Stars

Cited by 92 publications

References 91 publications

TOPoS

TOPoS

Metal-poor stars towards the Galactic bulge: A population potpourri

High-Resolution Spectroscopic Study of Extremely Metal-Poor Star Candidates From the Skymapper Survey

Contact Info

Product

Resources

About