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HE 1327-2326, AN UNEVOLVED STAR WITH [Fe/H] <-5.0. III. DOES ITS ATMOSPHERE REFLECT ITS NATAL COMPOSITION?
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
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2009 (English)In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 698, no 1, 410-416 p.Article in journal (Refereed) Published
Abstract [en]

Based on spectroscopic constraints derived from nonlocal thermodynamic equilibrium line formation, we explore the likely range of stellar parameters (T-eff and log g) for the hyper-metal-poor (HMP) star HE 1327-2326. Combining the constraints from Balmer line profiles and the Ca I/II ionization equilibrium, a subgiant stage of evolution is indicated. This result is further supported by spectrophotometric observations of the Balmer jump. If a higher T-eff value was used (as favored by some photometric calibrations), the spectroscopic analysis would indicate a turnoff-point stage of evolution. Using a stellar-structure code that treats the effects of atomic diffusion throughout the star in detail, we evolve a low-mass model star to reach the Hertzsprung-Russell-diagram position of HE 1327-2326 after roughly 13 Gyr. While the surface abundances are modified significantly (by more than 1 dex for the case of uninhibited diffusion), such corrections cannot resolve the discrepancy between the abundance inferred from the nondetection of the Li I resonance line at 6707 angstrom and the Wilkinson Microwave Anisotropy Probe based primordial lithium abundance. As there are numerous processes that can destroy lithium, any cosmological interpretation of a lower-than-expected lithium abundance at the lowest metallicities will have to await sample sizes of unevolved HMP stars that are 1 order of magnitude larger. The situation remains equally inconclusive concerning atomic-diffusion corrections. Here, attempts have to be made to better constrain internal mixing processes, both observationally and by means of sophisticated modeling. With constraints on additional mixing processes taken from a recent globular-cluster study, the likeliest scenario is that HE 1327-2326's surface abundances have undergone mild depletion (of order 0.2 dex).

Place, publisher, year, edition, pages
2009. Vol. 698, no 1, 410-416 p.
Keyword [en]
diffusion, stars: abundances, stars: evolution, stars: fundamental parameters, stars: individual (HE 1327-2326), stars: Population II
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:uu:diva-129043DOI: 10.1088/0004-637X/698/1/410ISI: 000266373700030OAI: oai:DiVA.org:uu-129043DiVA: diva2:337496
Available from: 2010-08-06 Created: 2010-08-05 Last updated: 2017-12-12Bibliographically approved

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