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

By A. Frebel, N. Christlieb, J. Norris, Timothy C. Beers, M. Bessell, J. Rhee, C. Fechner, B. Marsteller, S. Rossi, C. Thom and 2 more. 2006

161 citations recorded by the source corpus.

We present a sample of 1777 bright (9 < B < 14) metal-poor candidates selected from the Hamburg/ESO Survey (HES). Despite saturation effects present in the red portion of the HES objective-prism spectra, the data were recoverable and quantitative selection criteria could be applied to select the sample. Analyses of medium-resolution (~2 Å) follow-up spectroscopy of the entire sample, obtained with several 2-4 m class telescopes, yielded 145 new metal-poor stars with metallicity [Fe/H] < -2.0, of which 79 have [Fe/H] < -2.5 and 17 have [Fe/H] < -3.0. We also obtained C/Fe estimates for all of these stars. From this, we find a frequency of C-enhanced ([C/Fe] > 1.0) metal-poor ([Fe/H] < -2.0) giants of 9% ± 2%, which is lower than previously reported. However, the frequency rises to similar (>20%) and higher values with increasing distance from the Galactic plane. Although the numbers of stars at low metallicity are falling rapidly at the lowest metallicities, there is evidence that the fraction of carbon-enhanced metal-poor stars is increasing rapidly as a function of declining metallicity. For ~60 objects, high-resolution data have already been obtained; one of these, HE 1327-2326, is the new record holder for the most iron-deficient star known.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/64205569fab87629ac81d3294f22ffd32541558a

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In Astronomy and Astrophysics

1. A. Helmi
2. M. Walker
3. James S. Bullock
4. Timothy C. Beers
5. A. Frebel
6. J. Simon
7. M. Geha
8. Hans-Walter Rix

In Instrumentation

1. A. Helmi
2. M. Walker
3. James S. Bullock
4. Timothy C. Beers
5. A. Frebel
6. J. Simon
7. M. Geha
8. J. Norris

Citations in the corpus

• CARBON-ENHANCED METAL-POOR STARS IN SDSS/SEGUE. I. CARBON ABUNDANCE ESTIMATION AND FREQUENCY OF CEMP STARS (2013, methodology): “Frebel et al. (2006) followed Rossi et al.’s prescription to obtain [C/Fe] for a subset of 234 stars among 1777 metal-poor candidates from the HES survey, deriving a frequency of 9%±2% for VMP giants with [C/Fe]> +1.0.”
• Wind Roche-lobe overflow: Application to carbon-enhanced metal-poor stars (2013, methodology): “The observed CEMP to VMP ratio is approximately 20% (for example: 25% Marsteller et al. 2005; 9 ± 2% Frebel et al. 2006; 21 ± 2% Lucatello et al. 2006), with the fraction of CEMP stars rapidly increasing for decreasing iron content and for increasing distance from the Galactic plane (Carollo et al.…”
• HIGH-RESOLUTION SPECTROSCOPY OF EXTREMELY METAL-POOR STARS IN THE LEAST EVOLVED GALAXIES: URSA MAJOR II and COMA BERENICES (2009, methodology): “As has been known for quite a while, a large fraction of metal-poor halo stars are enriched in C, with numbers ranging from ∼ 15% (Frebel et al. 2006b; Cohen et al. 2005) to ∼ 25% (Marsteller et al. 2005).”
• DETAILED CHEMICAL ABUNDANCES IN THE r-PROCESS-RICH ULTRA-FAINT DWARF GALAXY RETICULUM 2 (2016, background): “The fraction of CEMP stars in the field increases with decreasing metallicity (e.g., Frebel et al. 2006; Carollo et al. 2012; Lee et al. 2013b; Placco et al. 2014).”
• Discovery of HE 1523–0901, a Strongly r-Process-enhanced Metal-poor Star with Detected Uranium (2007, background): “The giant HE 1523−0901 (V = 11.1) was found in a sample of bright metal-poor stars (Frebel et al. 2006) from the Hamburg/ESO Survey (HES).”
• The Pristine survey - I. Mining the Galaxy for the most metal-poor stars (2017, background): “…some indications for a further dependence of the presence of carbon-enhanced metal-poor stars and their sub-type on environment (with disk height, Frebel et al. (2006); in the inner Galaxy, Howes et al. (2015); in the inner versus outer halo, Carollo et al. (2014); and in the halo versus dwarf…”
• CARBON-ENHANCED METAL-POOR STAR FREQUENCIES IN THE GALAXY: CORRECTIONS FOR THE EFFECT OF EVOLUTIONARY STATUS ON CARBON ABUNDANCES (2014, background): “Also shown in the plot are the cumulative CEMP star frequencies of Frebel et al. (2006), Carollo et al. (2012), and Lee et al. (2013).”
• Stellar Abundances for the Galactic Archeology (SAGA) Database — Compilation of the Characteristics of Known Extremely Metal-Poor Stars (2008, methodology): “In this Figure, we have included the mediumresolution follow-up observations of “saturated stars” (9 < B < 14) from the HES provided by Frebel et al. (2006), and the cooler, carbon-rich stars from the HERES data sample of Lucatello et al. (2006).”
• Near-Field Cosmology with Extremely Metal-Poor Stars (2015, background): “…at the very least, theoretical models should address (i) the strong claims that the MDF and C-rich fraction change with Galactocentric distance (Frebel et al. 2006c, Carollo et al. 2010, 2012, An et al. 2013) and (ii) the need for element yields which recognize that C and Fe are decoupled for…”
• The stellar halo of the Galaxy (2008, methodology): “These stars are then followed up with medium-resolution spectroscopy (see, for example, Frebel et al. 2006).”
• Binarity in carbon-enhanced metal-poor stars (2014, background): “The fraction of CEMP stars is not just dependent on the metallicity, but also seems to vary with the distance above the Galactic plane (Frebel et al. 2006; Carollo et al. 2012) and between the inner and outer halo component (Carollo et al. 2012, 2014).”