Ultra-Lithium-Deficient Halo Stars and Blue Stragglers: A Common Origin?

Abstract

We present data for four ultra-Li-deficient, warm, halo stars. The Li deficiency of two of these is a new discovery. Three of the four stars have effective temperatures Teff ~ 6300 K, in contrast to previously known Li-deficient halo stars which spanned the temperature range of the Spite Plateau. In this paper we propose that these, and previously known ultra-Li-deficient halo stars, may have had their surface lithium abundances reduced by the same mechanism as produces halo field blue stragglers. Even though these stars have yet to reveal themselves as blue stragglers, they might be regarded as "blue-stragglers-to-be." In our proposed scenario, the surface abundance of Li in these stars could be destroyed (a) during the normal pre-main-sequence single star evolution of their low mass precursors, (b) during the post-main-sequence evolution of a evolved mass donor, and/or (c) via mixing during a mass-transfer event or stellar merger. The warmest Li-deficient stars at the turnoff would be regarded as emerging "canonical" blue stragglers, whereas cooler ones represent sub-turnoff-mass "blue-stragglers-to-be." The latter are presently hidden on the main sequence, Li depletion being possibly the clearest signature of their past history and future significance. Eventually, the main sequence turnoff will reach down to their mass, exposing those Li-depleted stars as canonical blue stragglers when normal stars of that mass evolve away. Arguing against this unified view is the observation that the three Li-depleted stars at Teff ~ 6300 K are all binaries, whereas very few of the cooler systems show evidence for binarity; it is thus possible that two separate mechanisms are responsible for the production of Li-deficient main-sequence halo stars.

23 pages including 3 figures. 2001, ApJ, 547, xxx (1 February)

References in corpus (5)

• Chemical composition of 90 F and G disk dwarfs
• Blue Straggler Stars: The Spectacular Population in M80
• The Host Stars of Extrasolar Planets Have Normal Lithium Abundances
• Extremely Metal-Poor Stars. VII. The Most Metal-Poor Dwarf, CS 22876-032
• On the lithium abundance dispersion in late-type Pleiades stars

Cited by in corpus (45)

• The Binary Frequency Among Carbon-Enhanced, s-Process Rich, Metal-Poor Stars
• Implications of WMAP observations on Li abundance and stellar evolution models
• First stars VII. Lithium in extremely metal poor dwarfs
• Stellar Collisions and the Interior Structure of Blue Stragglers
• Stellar Archaeology: a Keck Pilot Program on Extremely Metal- Poor Stars From the Hamburg/ESO Survey. III. The Lead (Pb) Star HE 0024-2523
• The Lithium Content of the Galactic Halo Stars
• Frontiers in Nuclear Astrophysics
• The Stellar Abundances for Galactic Archaeology (SAGA) Database II - Implications for Mixing and Nucleosynthesis in Extremely Metal-Poor Stars and Chemical Enrichment of the Galaxy
• Stellar Mixing and the Primordial Lithium Abundance
• Models of Metal Poor Stars with Gravitational Settling and Radiative Accelerations: I. Evolution and Abundance Anomalies
• VLT Observations of Turnoff stars in the Globular Cluster NGC 6397
• Light element evolution resulting from WMAP data
• The stellar origin of 7Li - Do AGB stars contribute a substantial fraction of the local Galactic lithium abundance?
• Abundances and Evolution of Lithium in the Galactic Halo and Disk
• Lithium abundances in CEMP stars
• Metal-poor Field Blue Stragglers: More Evidence for Mass Transfer
• Beryllium abundances and star formation in the halo and in the thick disk
• Metal-Poor Stars and the Chemical Enrichment of the Universe
• Mergers of close primordial binaries
• Signatures of rocky planet engulfment in HAT-P-4. Implications for chemical tagging studies
• Constraining cosmic scatter in the Galactic halo through a differential analysis of metal-poor stars
• Rapid rotation of ultra-Li-depleted halo stars and their association with blue stragglers
• Binary Blue Metal-Poor Stars: Evidence for AGB Mass Transfer
• Chromospherically young, kinematically old stars
• The Frequency of Field Blue-Straggler Stars in the Thick Disk and Halo System of the Galaxy
• Discovery of a thin lithium plateau among metal-poor red giant branch stars
• Mass Matters: No Evidence for Ubiquitous Lithium Production in Low-Mass Clump Giants
• Beryllium in Ultra-Lithium-Deficient Halo Stars - The Blue Straggler Connection
• Chemical evolution of the Galactic bulge as traced by microlensed dwarf and subgiant stars. VII. Lithium
• X-ray Evidence of the Common Envelope Phase of V471 Tauri
• The ${}^6$Li/${}^7$Li isotopic ratio in the metal-poor binary CS22876--032
• HIP 10725: The First Solar Twin/Analogue Field Blue Straggler
• A Critique of the Spite Plateau, and the Astration of Primordial Lithium
• Espresso observations of HE 0107$-$5240 and other CEMP-no stars with $[Fe/H]\le -4.5$
• The metal-poor end of the Spite plateau. II. Detailed chemical investigation
• High-speed stars. II. An unbound star, young stars, bulge metal-poor stars, and Aurora candidates
• Beryllium in the Ultra-Lithium-Deficient,Metal-Poor Halo Dwarf, G186-26
• Rotational Mixing and Lithium Depletion
• Accretion of chemically fractionated material on a wide binary with a blue straggler
• A coherent view of Li depletion and angular momentum transport to explain the Li plateau -- from Population II to Population I stars
• Something borrowed, something blue: The nature of blue metal-poor stars inferred from their colours and chemical abundances
• Intriguing Revelations from Lithium, Beryllium, and Boron
• Field Blue Stragglers and Related Mass Transfer Issues
• Neutron-capture elements in a sample of field metal-poor N-rich dwarfs
• Big Bang Nucleosynthesis, Population III, and Stellar Genetics in the Galactic Halo