Extremely metal‐poor stars in SDSS fields

Bonifacio, P.; Caffau, E.; François, P.; Sbordone, L.; Ludwig, H.‐G.; Spite, M.; Molaro, P.; Spite, F.; Cayrel, Roger; Hammer, F.; Hill, V.; Nonino, M.; Randich, S.; Stelzer, B.; Zaggia, S.

doi:10.1002/asna.201111528

Cited by 16 publications

(34 citation statements)

References 28 publications

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“…This is not the estimate provided by the SDSS pipeline (Allende Prieto et al 2008), but the one obtained by our analysis of the SDSS spectra. This estimate has already been mentioned in our previous papers (Bonifacio et al 2011Caffau et al 2011c). It has been obtained from our code for automatic analysis Abbo (Bonifacio & Caffau 2003).…”

Section: Discussionmentioning

confidence: 78%

“…We could observe twelve stars in the g magnitude range 17 to 19, half of which have [Fe/H] < −3.5. In the sample, SDSS J102915+172927 happens to be the most metal-poor star known to date (Caffau et al 2011b); SDSS J174259+253135 shows no evident feature except the Ca ii-K line and the G-band; three stars are EMP and low in α-elements (SDSS J082511+163459 Caffau et al 2011c, SDSS J153346+155701, and SDSS J161956+170539); SDSS J135516+001319 is a metal-poor star that is very low in α-elements (Bonifacio et al 2011).…”

Section: Discussionmentioning

confidence: 99%

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X-shooter GTO: evidence for a population of extremely metal-poor, alpha-poor stars

Caffau¹,

Bonifacio²,

François³

et al. 2013

A&A

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Context. The extremely metal-poor stars are the direct descendants of the first generation stars. They carry the chemical signature of the pristine Universe at the time they formed, shortly after the Big Bang. Aims. We aim to derive information about extremely metal-poor stars from their observed spectra. Methods. Four extremely metal-poor stars were selected from the Sloan Digital Sky Survey (SDSS) and observed during the guaranteed observing time of X-shooter. The X-shooter spectra were analysed using an automatic code, MyGIsFOS, which is based on a traditional analysis method. It makes use of a synthetic grid computed from one-dimensional, plane-parallel, hydrostatic model atmospheres. Results. The low metallicity derived from the SDSS spectra is confirmed here. Two kinds of stars are found. Two stars are confirmed to be extremely metal-poor, with no evidence of any enhancement in carbon. The two other stars are strongly enhanced in carbon. We could not derive iron abundance for one of them, while [Ca/H] is below -4.5. Two of the stars are members of the rare population of extremely metal-poor stars low in alpha elements.

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Section: Discussionmentioning

confidence: 78%

Section: Discussionmentioning

confidence: 99%

X-shooter GTO: evidence for a population of extremely metal-poor, alpha-poor stars

Caffau¹,

Bonifacio²,

François³

et al. 2013

A&A

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“…There is a growing number of metal-poor stars in the literature that show similar low [X/Fe] ratios (Nissen & Schuster 1997;Spite et al 2000;Ivans et al 2003;Cayrel et al 2004;Honda et al 2004;Cohen & Huang 2010;Bonifacio et al 2011;Venn et al 2012;Caffau et al 2013a;Yong et al 2013a). They have been called "α-poor" or "Fe-rich" metal-poor stars.…”

Section: Skymapper Metal-poor Stars Of Interestmentioning

confidence: 99%

“…Figure 16 plots the element abundance pattern of SMSS J034249.53-284216.0 (cyan squares, cyan bold line), along with other stars exhibiting low [X/Fe] ratios in the literature, relative to the mean abundances from the SkyMapper sample 15 (Table 10). We restrict the literature stars in Figure 16 to have [Fe/H] 2 < − , though we note that many other "Feenhanced" stars exist in the literature at higher metallicities (e.g., Nissen & Schuster 1997;Ivans et al 2003;Cohen & Huang 2010;Bonifacio et al 2011;Venn et al 2012). As has been noted in the literature (e.g., Yong et al 2013a), there is some scatter in the abundances of these stars.…”

Section: Skymapper Metal-poor Stars Of Interestmentioning

confidence: 99%

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

Jacobson

Keller

Frebel

et al. 2015

ApJ

127

145

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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.

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“…With these data in hand we aim to calibrate the metallicity estimates obtained from the low-resolution SDSS spectra to obtain a better statistics of the metal-poor tail of the MDF. Our project is a spin-off of a pilot survey conducted using French and Italian guaranteed observing time on X-Shooter: a sample of twelve stars has previously been analysed by Bonifacio et al (2011);Caffau et al (2011bCaffau et al ( ,c, 2012, and Caffau et al (2013). In addition, other useful data for our purposes can be found in Bonifacio et al (2012), who analysed 16 EMP stars observed with UVES that were selected in a similar manner from SDSS; Spite et al (2013), who analysed three stars selected because they were C-enhanced; and Behara et al (2010), who analysed another set of three C-enhanced stars extracted from the SDSS.…”

Section: Topos Goalsmentioning

confidence: 99%

TOPoS

Caffau

Bonifacio

Sbordone

et al. 2013

A&A

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Context. The metal-weak tail of the metallicity distribution function (MDF) of the Galactic Halo stars contains crucial information on the formation mode of the first generation of stars. To determine this observationally, it is necessary to observe large numbers of extremely metal-poor stars. Aims. We present here the Turn-Off Primordial Stars survey (TOPoS) that is conducted as an ESO Large Programme at the VLT. This project has four main goals: (i) to understand the formation of low-mass stars in a low-metallicity gas: determine the metal-weak tail of the halo MDF below [M/H] = −3.5; in particular, we aim at determining the critical metallicity, that is the lowest metallicity sufficient for the formation of low-mass stars; (ii) to determine in extremely metal-poor stars the relative abundances of the elements that are the signature of the massive first stars; (iii) to determine the trend of the lithium abundance at the time when the Galaxy formed; and (iv) to derive the fraction of C-enhanced extremely metal-poor stars with respect to normal extremely metal-poor stars. The large number of stars observed in the SDSS provides a good sample of candidate stars at extremely low metallicity. Methods. Candidates with turn-off colours down to magnitude g = 20 were selected from the low-resolution spectra of SDSS by means of an automated procedure. X-Shooter has the potential of performing the necessary follow-up spectroscopy, providing accurate metallicities and abundance ratios for several key elements for these stars. Results. We present here the stellar parameters of the first set of stars. The nineteen stars range in iron abundance between -4.1 and −2.9 dex relative to the Sun. Two stars have a high radial velocity and, according to our estimate of their kinematics, appear to be marginally bound to the Galaxy and are possibly accreted from another galaxy.

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Extremely metal‐poor stars in SDSS fields

Cited by 16 publications

References 28 publications

X-shooter GTO: evidence for a population of extremely metal-poor, alpha-poor stars

X-shooter GTO: evidence for a population of extremely metal-poor, alpha-poor stars

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

TOPoS

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