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Titolo:
Oxygen in the very early galaxy
Autore:
Israelian, G; Rebolo, R; Lopez, RJG; Bonifacio, P; Molaro, P; Basri, G; Shchukina, N;
Indirizzi:
Inst Astrofis Canarias, E-38200 La Laguna, Tenerife, Spain Inst Astrofis Canarias La Laguna Tenerife Spain E-38200 , Tenerife, Spain Osservatorio Astron Trieste, I-34131 Trieste, Italy Osservatorio Astron Trieste Trieste Italy I-34131 I-34131 Trieste, Italy Univ Calif Berkeley, Dept Astron, Berkeley, CA 94720 USA Univ Calif Berkeley Berkeley CA USA 94720 Astron, Berkeley, CA 94720 USA Natl Acad Sci, Main Astron Observ, UA-03680 Kyiv 127, Ukraine Natl Acad Sci Kyiv Ukraine 127 Astron Observ, UA-03680 Kyiv 127, Ukraine
Titolo Testata:
ASTROPHYSICAL JOURNAL
fascicolo: 2, volume: 551, anno: 2001,
parte:, 1
pagine: 833 - 851
SICI:
0004-637X(20010426)551:2<833:OITVEG>2.0.ZU;2-L
Fonte:
ISI
Lingua:
ENG
Soggetto:
METAL-POOR STARS; FE-I LINES; RELATIVE OSCILLATOR-STRENGTHS; SOLAR IRON ABUNDANCE; HALO STARS; PRECISION-MEASUREMENT; ATMOSPHERIC PARAMETERS; BERYLLIUM ABUNDANCES; CHEMICAL-COMPOSITION; RADIATIVE-TRANSFER;
Keywords:
Galaxy : abundances; Galaxy : evolution; nuclear reactions, nucleosynthesis, abundances; stars : abundances; stars : late-type; stars : Population II;
Tipo documento:
Review
Natura:
Periodico
Settore Disciplinare:
Physical, Chemical & Earth Sciences
Citazioni:
108
Recensione:
Indirizzi per estratti:
Indirizzo: Israelian, G Inst Astrofis Canarias, E-38200 La Laguna, Tenerife, Spain Inst Astrofis Canarias La Laguna Tenerife Spain E-38200 pain
Citazione:
G. Israelian et al., "Oxygen in the very early galaxy", ASTROPHYS J, 551(2), 2001, pp. 833-851

Abstract

Oxygen abundances in a sample of ultra-metal-poor subdwarfs have been derived from measurements of the oxygen triplet at 7771-5 Angstrom and OH linesin the near-UV performed in high-resolution and high signal-to-noise ratiospectra obtained with WHT/UES, Keck I/HIRES, and VLT/UVES. Our Fe abundances were derived in LTE and then corrected for non-LTE (NLTE) effects. The new oxygen abundances confirm previous findings for a progressive linear rise in the oxygen-to-iron ratio with a slope -0.33 +/- 0.02 from solar metallicity to [Fe/H] similar to -3. A slightly higher slope would be obtained ifthe Fe NLTE corrections were not considered. Below [Fe/H] = -2.5 our starsshow [O/Fe] ratios as high as similar to1.17 (G64-12), which can be interpreted as evidence for oxygen overproduction in the very early epoch of the formation of the halo, possibly associated with supernova events with very massive progenitor stars. We show that the arguments against this linear trend given by Fulbright & Kraft in 1999, based on the LTE Fe analysis of twometal-poor stars, cannot be sustained when an NLTE analysis is performed. We discuss how the Fulbright & Kraft LTE ionization balance of Fe lines underestimates the gravity of the very metal-poor star BD +23 degrees 3130 ([Fe/H] = -2.43) and how this leads to an underestimation of the oxygen abundance derived from the forbidden line. Gravities from Hipparcos appear to be in good agreement with those determined in NLTE, giving higher values than previously assumed, which reduces the discrepancies between the oxygen abundances determined from OH, triplet, and forbidden lines. Using one-dimensional models, our analysis of three oxygen indicators available for BD +23 degrees 3130 gives an average [O/Fe] ratio of 0.78(-0.18)(+0.15). The high oxygen abundances at very low metallicities do not pose a problem to theoretical modeling since there is a range of parameters in the calculations of nucleosynthesis yields from massive stars at low metallicities that can accommodate our results.

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Documento generato il 24/09/20 alle ore 08:13:58