Bright Metal‐poor Stars from the Hamburg/ESO Survey. I. Selection and Follow‐up Observations from 329 Fields

Frebel, Anna; Christlieb, N.; Norris, John E.; Bessell, M. S.; Rhee, Jaehyon; Fechner, C.; Marsteller, B.; Rossi, Silvia; Thom, Christopher; Wisotzki, L.; Reimers, D.

doi:10.1086/508506

Cited by 185 publications

(234 citation statements)

References 66 publications

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“…We do not know the reason for this behaviour, but we hypothesise that the samples towards the inner and outer regions of A122, page 5 of 11 A&A 583, A122 (2015) the Galaxy may belong to two different galactic populations. In fact, an increasing trend of the C star/M star ratio with [Fe/H] in the Galaxy is reported in the literature (e.g., Frebel et al 2006) and in the Large Magellanic Cloud (Blanco et al 1980;Cioni & Habing 2003). At the same time, a negative trend with [Fe/H] has been reported by a variety of studies (e.g., Boeche et al 2013;Bergemann et al 2014), at low values of galactic vertical height (|Z| < 300−400 pc).…”

Section: Resultsmentioning

confidence: 78%

The variability behaviour of CoRoT M-giant stars

Lopes

Neves

Leão

et al. 2015

A&A

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Context. For six years the Convection, Rotation, and planetary Transits (CoRoT) space mission has been acquiring photometric data from more than 100 000 point sources towards and directly opposite the inner and outer regions of the Galaxy. The high temporal resolution of the CoRoT data, combined with the wide time span of the observations, enabled the study of short-and long-time variations in unprecedented detail. Aims. The aim of this work is to study the variability and evolutionary behaviour of M-giant stars using CoRot data. Methods. From the initial sample of 2534 stars classified as M giants in the CoRoT databases, we selected 1428 targets that exhibit well defined variability, by visual inspection. Then, we defined three catalogues: C1 -stars with T eff < 4200 K and LCs displaying semi-sinusoidal signatures; C2 -rotating variable candidates with T eff > 4200 K; C3 -long-period variable candidates (with LCs showing a variability period up to the total time span of the observations). The variability period and amplitude of C1 stars were computed using Lomb-Scargle and harmonic fit methods. Finally, we used C1 and C3 stars to study the variability behaviour of M-giant stars. Results. The trends found in the V − I vs. J − K colour-colour diagram are in agreement with standard empirical calibrations for M giants. The sources located towards the inner regions of the Galaxy are distributed throughout the diagram, while the majority of the stars towards the outer regions of the Galaxy are spread between the calibrations of M giants and the predicted position for carbon stars. The stars classified as supergiants follow a different sequence from the one found for giant stars. We also performed a Kolmogorov-Smirnov (KS) test of the period and amplitude of stars towards the inner and outer regions of the Galaxy. We obtained a low probability that the two samples came from the same parent distribution. The observed behaviour of the period-amplitude and period-effective temperature (T eff ) diagrams are, in general, in agreement with those found for Kepler sources and ground based photometry, with pulsation being the dominant cause responsible for the observed modulation. We also conclude that short-time variations on M-giant stars do not exist or are very rare, and the few cases we found are possibly related to biases or background stars.

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Section: Resultsmentioning

confidence: 78%

The variability behaviour of CoRoT M-giant stars

Lopes

Neves

Leão

et al. 2015

A&A

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“…6 we have included only unevolved stars since giant stars may be internally "mixed" (Spite et al 2005(Spite et al , 2006 and the C abundance may thus be decreased by an amount that is generally difficult to estimate. We have included in the plot only stars from the literature that have a measured Ba abundance or a significant upper limit (Sivarani et al 2006;Frebel et al 2005Frebel et al , 2006Thompson et al 2008;Aoki et al 2008;Behara et al 2010;Masseron et al 2010Masseron et al , 2012Yong et al 2013;Cohen et al 2013;Li et al 2015), so as to have some indication on their classification as CEMP-no, CEMP-s, or CEMP-rs. In order to clearly define the behaviour of the carbon abundance at low metallicity, we have also included the ultra-iron-poor subgiant HE 1327-2326 (Frebel et al 2005Cohen et al 2013) and SDSS J1619+1705 (Caffau et al 2013a), even though their Ba abundance is undetermined.…”

Section: On the Carbon Abundances In Cemp Starsmentioning

confidence: 99%

TOPoS

Bonifacio

Caffau

Spite

et al. 2015

A&A

174

232

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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.

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“…Li, C, Mg and Ca have been measured and there are upper limits on several other elements. HE 1327-2326 (Frebel et al 2006(Frebel et al , 2008 and HE 1017-5240 (Christlieb E-mail: oclark01@uvic.ca Low-energy or faint supernovae with strong fallback would have either very little or no nucleosynthetic contribution from the supernova explosion (Keller et al 2014;Takahashi et al 2014;Marassi et al 2014). However, many the best fit models proposed for CEMP-no stars are within the mass range where Pop III and the lowest-metallicity stars are expected to collapse directly into black holes with no supernova explosion (Heger et al 2003).…”

Section: Introductionmentioning

confidence: 99%

Pop III i-process nucleosynthesis and the elemental abundances of SMSS J0313−6708 and the most iron-poor stars

Clarkson

Herwig

Pignatari

2017

Monthly Notices of the Royal Astronomical Society: Letters

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We have investigated a highly energetic H-ingestion event during shell He burning leading to H-burning luminosities of log(L H /L ) ∼ 13 in a 45M Pop III massive stellar model. In order to track the nucleosynthesis which may occur in such an event, we run a series of single-zone nucleosynthesis models for typical conditions found in the stellar evolution model. Such nucleosynthesis conditions may lead to i-process neutron densities of up to ∼ 10 13 cm −3 . The resulting simulation abundance pattern, where Mg comes from He burning and Ca from the i process, agrees with the general observed pattern of the most iron-poor star currently known, SMSS J031300.36-670839.3. However, Na is also efficiently produced in these i process conditions, and the prediction exceeds observations by ∼ 2.5dex. While this probably rules out this model for SMSS J031300.36-670839.3, the typical i-process signature of combined He burning and i process of higher than solar [Na/Mg], [Mg/Al] and low [Ca/Mg] is reproducing abundance features of the two next most iron-poor stars HE 1017-5240 and HE 1327-2326 very well. The i process does not reach Fe which would have to come from a low level of additional enrichment. i process in hyper-metal poor or Pop III massive stars may be able to explain certain abundance patterns observed in some of the most-metal poor CEMP-no stars.

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Bright Metal‐poor Stars from the Hamburg/ESO Survey. I. Selection and Follow‐up Observations from 329 Fields

Cited by 185 publications

References 66 publications

The variability behaviour of CoRoT M-giant stars

The variability behaviour of CoRoT M-giant stars

TOPoS

Pop III i-process nucleosynthesis and the elemental abundances of SMSS J0313−6708 and the most iron-poor stars

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