The Binary Frequency Among Carbon-enhanced, s-Process-rich, Metal-poor Stars

By S. Lucatello, S. Tsangarides, Timothy C. Beers, E. Carretta, R. Gratton, S. Ryan. 2004

259 citations recorded by the source corpus.

We discuss radial velocities for a sample of carbon-enhanced, s-process-rich, very metal-poor (CEMP-s) stars, analyzed with high-resolution spectroscopy obtained over multiple epochs. We find that ~68% of the stars in the sample show evidence of radial velocity variations. The expected detection fraction for these stars, adopting the measured binary fraction in the field (~60%) and assuming that they share the same period and eccentricity distribution, is ~22%. Even if one assumes that the true binary fraction of these stars is 100%, the expected detection percentage is ~36%. These values indicate that the binary fraction among CEMP-s stars is higher than the field binary fraction, suggesting that all of these objects are in double (or multiple) systems. The fact that the observed frequency of velocity variation exceeds the expected detection fraction in the case of an assumed binary fraction of 100% is likely due to a more restricted distribution of orbital periods for these objects, as compared to normal field binaries. Our results indicate that CEMP-s stars are the metal-poor analogs of classical CH stars.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/efd567112e6fa977dbe326befa2661f716ae4d93

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In Astronomy and Astrophysics

1. Timothy C. Beers
2. A. Karakas
3. A. Frebel
4. Roberto Gallino
5. J. Norris
6. C. Sneden
7. Martin Asplund
8. M. Lugaro

In Instrumentation

1. A. Frebel
2. Timothy C. Beers
3. A. Karakas
4. J. Norris
5. Roberto Gallino
6. C. Sneden
7. A. Helmi
8. M. Lugaro

Citations in the corpus

• THE MOST METAL-POOR STARS. II. CHEMICAL ABUNDANCES OF 190 METAL-POOR STARS INCLUDING 10 NEW STARS WITH [Fe/H] ⩽ −3.5,, (2012, background): “The CEMP-s stars are the majority population,∼80% of all CEMP objects (Aoki 2010), and radial-velocity studies have revealed that the observed binary frequency in this subclass is consistent with a binary fraction of 100% (Lucatello et al. 2005).”
• The First Stellar Cluster (2007, background): “Recent observations suggest that extremely metal-poor low-mass stars have a higher binary fraction than that found for normal metal-poor stars, and that the period distribution of these binary systems is also skewed towards tight, short-period binaries (Lucatello et al. 2005).”
• Neutron-Capture Elements in the Early Galaxy (2008, background): “Lucatello et al. (2005) detected radial velocity variations in 60% of a sample of C- and s-rich stars and argued on statistical grounds (see also Cohen et al. 2006) that nearly all stars of this type must be binaries.”
• The Hamburg/ESO R-process enhanced star survey (HERES) - III. HE 0338-3945 and the formation of the r + s stars (2006, background): “A recent study by Lucatello et al. (2005) suggests all CEMP stars are multiple systems.”
• The Close Binary Fraction of Solar-type Stars Is Strongly Anticorrelated with Metallicity (2018, background): “We do not include extremely metal-poor giants enriched with s-process elements, e.g., barium, which exhibit a very large SB fraction of ≈80% and are clearly the result of post-MS binary mass transfer (Jorissen et al. 1998; Lucatello et al. 2005; Hansen et al. 2016b).”
• Massive AGB models of low metallicity: the implications for the self-enrichment scenario in metal-poor globular clusters (2009, background): “The presence of enhanced C and N in extremely metal poor low mass stars presently observed is generally attributed to mass transfer from a previously evolving AGB companion (e.g. Lucatello et al. 2005).”
• Near-Field Cosmology with Extremely Metal-Poor Stars (2015, background): “The CEMP-s subclass represents a large fraction of the C-rich population, the chemical enrichment of which is almost certainly driven by mass transfer across a binary system containing an erstwhile asymptotic giant branch (AGB) star (e.g., Lucatello et al. 2005, and references therein).”
• Chemical tagging with APOGEE: Discovery of a large population of N-rich stars in the inner Galaxy (2016, background): “Observations of CH stars, which are objects of similar nature (see below for details), are typically of the order of several years (see, e.g., Lucatello et al. 2005a).”
• Carbon-enhanced Metal-poor Stars. I. Chemical Compositions of 26 Stars (2006, methodology): “The fraction of binary stars among CEMP stars has been recently studied by Lucatello et al. (2005), who concluded that all CEMP stars with s-process element overabundances (which Beers & Christlieb [2005] refer to as CEMP-s stars) could statistically 8 There exists one recently discovered…”
• THE DISCOVERY AND ANALYSIS OF VERY METAL-POOR STARS IN THE GALAXY (2005, background): “The lower-mass companion is presently observed to be carbon-rich, whereas the higher-mass carbon-producing star is now a faint white dwarf (see, e.g., Lucatello et al. 2005).”
• The s-Process in Low Metallicity Stars. II. Interpretation of High-Resolution Spectroscopic Observations with AGB models (2011, background): “A radial velocity study by Lucatello et al. (2005) suggests that all CEMP-s stars belong to double (or multiple) systems (see also Tsangarides 2005; Preston 2009).”
• Binarity in carbon-enhanced metal-poor stars (2014, methodology): “We note that three stars in their sample were classified as CEMP-s stars by Lucatello et al. (2005) and are present in both samples.”
• The first galaxies : assembly, cooling and the onset of turbulence (2008, background): “…and oxygen enhancements, which could be due to unusual abundance patterns produced by enrichment from BH-forming Pop III SNe (Umeda & Nomoto 2003), or due to mass transfer from a close binary companion, whose frequency is predicted to increase with decreasing metallicity (Lucatello et al. 2005).”
• CARBON-ENHANCED METAL-POOR STAR FREQUENCIES IN THE GALAXY: CORRECTIONS FOR THE EFFECT OF EVOLUTIONARY STATUS ON CARBON ABUNDANCES (2014, unknown): “Radial-velocity monitoring (e.g., Lucatello et al. 2005) confirms the binarity of the majority of these CEMP stars, and extensive studies have been conducted to compare the observed abundance patterns with theoretical models (e.g., Bisterzo et al. 2011; Placco et al. 2013; Hollek et al. 2014).”
• THE s-PROCESS IN ASYMPTOTIC GIANT BRANCH STARS OF LOW METALLICITY AND THE COMPOSITION OF CARBON-ENHANCED METAL-POOR STARS (2011, background): “…the presence of an originally more massive binary companion to the observed star, which produced C and s-process elements during its asymptotic giant branch (AGB) phase and transferred them to its companion via mass transfer, by either Roche-Lobe overflow or wind accretion (Lucatello et al. 2005).”
• Wind Roche-lobe overflow: Application to carbon-enhanced metal-poor stars (2013, background): “Lucatello et al. (2005a) and Komiya et al. (2007) come to the conclusion that an IMF biased toward intermediate-mass stars is required to reproduce the fraction of CEMP/VMP stars measured in the Halo.”