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

Jacobson, Heather R.; Keller, Stefan; Frebel, Anna; Casey, Andrew R.; Asplund, Martin; Bessell, M. S.; Costa, G. S. Da; Lind, Karin; Marino, A. F.; Norris, John E.; Peña, José Martínez; Schmidt, B.; Tisserand, Patrick; Walsh, Jennifer; Yong, David; Yu, Qinsi

doi:10.1088/0004-637x/807/2/171

Cited by 129 publications

(165 citation statements)

References 123 publications

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“…This 'commissioning-era' survey, which is superceded by the current work, led to the discovery of the most ironpoor star known SMSS J031300.36-670839.3 (usually abbreviated to SMSS J0313-6708), which has [Fe/H] < -6.5 (3D, NLTE) (Keller et al 2014;Bessell et al 2015;Nordlander et al 2017). A total of 139 additional Galactic halo EMP candidates from the commissioning-era survey were also followed-up at high dispersion to provide detailed abundance information: 44 stars were shown to have [Fe/H] -3.0 and 3 have [Fe/H] ≈ -4.0 (Jacobson et al 2015;Marino et al 2019). Full descriptions of the derived abundances and abundance ratios for these stars are given and discussed in Jacobson et al (2015) and Marino et al (2019).…”

Section: Introductionmentioning

confidence: 99%

The SkyMapper DR1.1 search for extremely metal-poor stars

Costa

Bessell

Mackey

et al. 2019

Monthly Notices of the Royal Astronomical Society

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We present and discuss the results of a search for extremely metal-poor stars based on photometry from data release DR1.1 of the SkyMapper imaging survey of the southern sky. In particular, we outline our photometric selection procedures and describe the low-resolution (R ≈ 3000) spectroscopic follow-up observations that are used to provide estimates of effective temperature, surface gravity and metallicity ([Fe/H]) for the candidates. The selection process is very efficient: of the 2618 candidates with low-resolution spectra that have photometric metallicity estimates less than or equal to -2.0, 41% have [Fe/H] -2.75 and only ∼7% have [Fe/H] > -2.0 dex. The most metal-poor candidate in the sample has [Fe/H] < -4.75 and is notably carbon-rich. Except at the lowest metallicities ([Fe/H] < -4), the stars observed spectroscopically are dominated by a 'carbon-normal' population with [C/Fe] 1D,LT E +1 dex. Consideration of the A(C) 1D,LT E versus [Fe/H] 1D,LT E diagram suggests that the current selection process is strongly biased against stars with A(C) 1D,LT E > 7.3 (predominantly CEMP-s) while any bias against stars with A(C) 1D,LT E < 7.3 and [C/Fe] LT E > +1 (predominantly CEMP-no) is not readily quantifiable given the uncertainty in the SkyMapper v-band DR1.1 photometry. We find that the metallicity distribution function of the observed sample has a power-law slope of ∆(Log N)/∆[Fe/H] = 1.5 ± 0.1 dex per dex for -4.0 [Fe/H] -2.75, but appears to drop abruptly at [Fe/H] ≈ -4.2, in line with previous studies.

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Section: Introductionmentioning

confidence: 99%

The SkyMapper DR1.1 search for extremely metal-poor stars

Costa

Bessell

Mackey

et al. 2019

Monthly Notices of the Royal Astronomical Society

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“…Despite several surveys specifically designed to discover extremely metal-poor objects in the halo (e.g., Beers et al 1992;Cayrel et al 2001;Christlieb 2003;Jacobson et al 2015) and bulge (Howes et al 2015), no metal-free stars have been detected, and only a single star indicating pollution from pairinstability supernovae (Aoki et al 2014; but see also Aoki et al 2015), although this may be a selection effect (Karlsson et al 2008). A handful of extremely metal-poor stars have been identified to exhibit a chemical composition indicative of pollution from one or just a few core-collapse supernovae (e.g., Christlieb et al 2002;Frebel et al 2005;Caffau et al 2011), with SMSS0313-6708 being the most likely candidate to have been polluted by a single supernova (Keller et al 2014;Bessell et al 2015).…”

Section: Introductionmentioning

confidence: 99%

3D NLTE analysis of the most iron-deficient star, SMSS0313-6708

Nordlander

Amarsi

Lind

et al. 2016

A&A

104

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Context. Models of star formation in the early universe require a detailed understanding of accretion, fragmentation and radiative feedback in metal-free molecular clouds. Different simulations predict different initial mass functions of the first stars, ranging from predominantly low-mass (0.1−10 M ), to massive (10−100 M ), or even supermassive (100−1000 M ). The mass distribution of the first stars should lead to unique chemical imprints on the low-mass second and later generation metal-poor stars still in existence. The chemical composition of SMSS0313-6708, which has the lowest abundances of Ca and Fe of any star known, indicates it was enriched by a single massive supernova. Aims. The photospheres of metal-poor stars are relatively transparent in the UV, which may lead to large three-dimensional (3D) effects as well as departures from local thermodynamical equilibrium (LTE), even for weak spectral lines. If 3D effects and departures from LTE (NLTE) are ignored or treated incorrectly, errors in the inferred abundances may significantly bias the inferred properties of the polluting supernovae. We redetermine the chemical composition of SMSS0313-6708 by means of the most realistic methods available, and compare the results to predicted supernova yields. Methods. A 3D hydrodynamical Stagger model atmosphere and 3D NLTE radiative transfer were applied to obtain accurate abundances for Li, Na, Mg, Al, Ca and Fe. The model atoms employ realistic collisional rates, with no calibrated free parameters. Results. We find significantly higher abundances in 3D NLTE than 1D LTE by 0.8 dex for Fe, and 0.5 dex for Mg, Al and Ca, while Li and Na are unaffected to within 0.03 dex. In particular, our upper limit for [Fe/H] is now a factor ten larger, at [Fe/H] < −6.53 (3σ), than previous estimates based on 3D NLTE (i.e., using averaged 3D models). This higher estimate is due to a conservative upper limit estimation, updated NLTE data, and 3D− 3D NLTE differences, all of which lead to a higher abundance determination. Conclusions. We find that supernova yields for models in a wide range of progenitor masses reproduce the revised chemical composition. In addition to massive progenitors of 20−60 M exploding with low energies (1−2 B, where 1 B = 10 51 erg), we also find good fits for progenitors of 10 M , with very low explosion energies (<1 B). We cannot reconcile the new abundances with supernovae or hypernovae with explosion energies above 2.5 B, nor with pair-instability supernovae.

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“…Sample from Jacobson et al (2015) We applied our framework to measure [C/Fe] values to a sample of high-resolution Magellan/MIKE spectra of MP halo stars selected from the SkyMapper survey. These spectra were degraded to match the resolution of our medium-resolution spectra and injected with Gaussian noise to bring the S/N down to 20 Å −1 .…”

Section: External Validation: Comparison To Skymappermentioning

confidence: 99%

“…These spectra were degraded to match the resolution of our medium-resolution spectra and injected with Gaussian noise to bring the S/N down to 20 Å −1 . High-resolution [C/Fe] abundances computed by Jacobson et al (2015) were used as reference values.…”

Section: External Validation: Comparison To Skymappermentioning

confidence: 99%

Detection of a Population of Carbon-enhanced Metal-poor Stars in the Sculptor Dwarf Spheroidal Galaxy^∗

Chiti

Simon

Frebel

et al. 2018

ApJ

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The study of the chemical abundances of metal-poor stars in dwarf galaxies provides a venue to constrain paradigms of chemical enrichment and galaxy formation. Here we present metallicity and carbon abundance measurements of 100 stars in Sculptor from medium-resolution (R ∼ 2000) spectra taken with the Magellan/ Michigan Fiber System mounted on the Magellan-Clay 6.5 m telescope at Las Campanas Observatory. We identify 24 extremely metal-poor star candidates ([Fe/H] < −3.0) and 21 carbon-enhanced metal-poor (CEMP) star candidates. Eight carbon-enhanced stars are classified with at least 2σ confidence, and five are confirmed as such with follow-up R ∼ 6000 observations using the Magellan Echellette Spectrograph on the Magellan-Baade 6.5 m telescope. We measure a CEMP fraction of 36% for stars below [Fe/H] = −3.0, indicating that the prevalence of carbon-enhanced stars in Sculptor is similar to that of the halo (∼43%) after excluding likely CEMP-s and CEMPr/s stars from our sample. However, we do not detect that any CEMP stars are strongly enhanced in carbon ([C/Fe] > 1.0). The existence of a large number of CEMP stars both in the halo and in Sculptor suggests that some halo CEMP stars may have originated from accreted early analogs of dwarf galaxies.

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

Cited by 129 publications

References 123 publications

The SkyMapper DR1.1 search for extremely metal-poor stars

The SkyMapper DR1.1 search for extremely metal-poor stars

3D NLTE analysis of the most iron-deficient star, SMSS0313-6708

Detection of a Population of Carbon-enhanced Metal-poor Stars in the Sculptor Dwarf Spheroidal Galaxy^∗

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

Cited by 129 publications

References 123 publications

The SkyMapper DR1.1 search for extremely metal-poor stars

The SkyMapper DR1.1 search for extremely metal-poor stars

3D NLTE analysis of the most iron-deficient star, SMSS0313-6708

Detection of a Population of Carbon-enhanced Metal-poor Stars in the Sculptor Dwarf Spheroidal Galaxy∗

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Detection of a Population of Carbon-enhanced Metal-poor Stars in the Sculptor Dwarf Spheroidal Galaxy^∗