The surface carbon and nitrogen abundances in models  of
ultra metal-poor stars

Schlattl, Helmut; Salaris, Maurizio; Cassisi, S.; Weiß, Achim

doi:10.1051/0004-6361:20020813

Cited by 33 publications

(53 citation statements)

References 35 publications

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“…However, the possibility that this star has been formed of pristine gas cannot be excluded: Shigeyama Tsujimoto & Yoshii (2003) conclude that HE 0107-5240 is a Pop III star with the surface polluted by accreted interstellar gas already enriched with metals. In this scenario overabundant C and N in the envelope can be produced during the core helium flash as suggested by (Weiss et al 2000;Schlattl et al 2002). The estimates presented in this paper show that a small fraction of baryons processed by shocks in merger events may indeed become extremely cold and form low mass stars of the first generation.…”

Section: Star Formationmentioning

confidence: 55%

Low‐temperature primordial gas in merging halos

Vasiliev

Shchekinov

2008

Astron Nachr

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Thermal regime of the baryons behind shock waves arising in the process of virialization of dark matter halos is governed at cetrain conditions by radiation of HD lines. A small fraction of the shocked gas can cool down to the temperature of the cosmic microwave background (CMB). We estimate an upper limit for this fraction: at z = 10 it increases sharply from about q T ∼ 10 −3 for dark halos of M = 5 × 10 7 M⊙ to ∼ 0.1 for halos with M = 10 8 M⊙. Further increase of the halo mass does not lead however to a significant growth of qT -the asymptotic value for M ≫ 10 8 M⊙ is of 0.3: We estimate star formation rate associated with such shock waves, and show that they can provide a small but not negligible fraction of the star formation. We argue that extremely metal-poor low-mass stars in the Milky Way may have been formed from primordial gas behind such shocks.

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Section: Star Formationmentioning

confidence: 55%

Low‐temperature primordial gas in merging halos

Vasiliev

Shchekinov

2008

Astron Nachr

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“…Fujimoto et al 1990, Cassisi et al 1996, Siess et al 2002, Schlattl et al 2002, Picardi et al 2004, Suda et al 2004. Most of these stars show abundances that conform to a simple Galactic chemical evolution line (see Figure 1).…”

Section: Introductionmentioning

confidence: 82%

Low-Mass Extremely Metal-Poor Stellar Models: Yields, Uncertainties and the Galactic Halo Stars

Campbell¹,

Lattanzio²

2008

Proc. IAU

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Abstract.We have calculated a set of low-mass (0.85 M M 3.0 M ) zero metallicity and extremely metal-poor (−6.5 [Fe/H] −3.0) stellar models, including nucleosynthetic yields for 74 species. As far as we are aware these are the first detailed yields in the mass and metallicity range considered. Due to the difficulty in modelling such stars the yields naturally contain numerous uncertainties, and thus present interesting challenges for future stellar modelling. We briefly present some results in the context of the Galactic Halo star observations, and also discuss qualitatively some of the uncertainties in the modelling. We conclude by suggesting that much work is still necessary in this research area. For example, multidimensional fluid dynamics models are needed to simulate the violent proton ingestion events that occur during the core He flash and early TPAGB, observations and theory of mass loss at low metallicities are needed, the effects of reaction rate uncertainties need to be quantified, and low temperature opacities variable in carbon (and nitrogen) need to be included in the models.

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“…Since the reviews by Castellani (2000) and Chiosi (2000), theoretical material has been published by Fujimoto et al (2000), Marigo et al (2001), Schlattl et al (2001), Schlattl et al (2002), Siess et al (2002) and others, revealing original aspects of the evolution of these stars. Nonetheless, the results are still affected by fundamental uncertainties in the description of convective overshoot, mass loss, etc., especially in the initial-mass range 0.7−0.8 M , which includes the stars of concern here, so these results should only be used as guidelines to help us select a scenario.…”

Section: (Crypto-) Pop III Progenitor (Single Star)mentioning

confidence: 99%

“…HEFM is favoured by low stellar mass, low heavy element pollution of the atmosphere, the inclusion of element diffusion and the absence of convective overshoot (Schlattl et al 2002). Including convective overshoot (which is likely to exist on other grounds) may inhibit HEFM, but evolution then proceeds to the thermal-pulse AGB phase with again the dredge-up of large amounts of CN and, this time, a non negligible amount of oxygen.…”

Section: (Crypto-) Pop III Progenitor (Single Star)mentioning

confidence: 99%

“…Including convective overshoot (which is likely to exist on other grounds) may inhibit HEFM, but evolution then proceeds to the thermal-pulse AGB phase with again the dredge-up of large amounts of CN and, this time, a non negligible amount of oxygen. Thus, the production of oxygen and heavier elements, although problematic in these stars, is possible in some scenarios (Schlattl et al 2002;Siess et al 2002). Many of the most metal-poor stars are known to be nitrogen-rich carbon stars with very large [C/Fe] (Rossi et al 1999;Christlieb et al 2004;Marsteller et al 2003), suggesting that dredge-up of CN can indeed take place in extremely metalpoor stars, although alternative explanations are possible (e.g., Umeda & Nomoto 2003).…”

Section: (Crypto-) Pop III Progenitor (Single Star)mentioning

confidence: 99%

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Endogenous oxygen in the extremely metal-poor planetary nebula PN G135.9+55.9

Pequignot¹,

Tsamis²

2005

A&A

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Abstract. It is shown that, in contrast to recent claims, oxygen (and helium) may not be extraordinarily underabundant in the new galactic halo planetary nebula (GHPN) PN G135.9+55.9 (hereafter PN G135). Determining elemental abundances in hot, highly ionized objects such as PN G135 depends critically on a proper description of the collisional excitation of the hydrogen Balmer lines, the departure from Case B recombination of hydrogen, the underlying stellar absorption lines, the shape of the primary continuum and the ionization equilibrium of highly ionized species of both oxygen and neon. Conversely, PN G135provides unique checks of atomic data in unusual conditions: the H  collision strengths obtained by Aggarwal et al. (1991) for 1s − n transitions (3 ≤ n ≤ 5) are too large, while those obtained by Anderson et al. (2002) are acceptable. Empirical collision strengths are presented for n > 5. Photoionization models of PN G135 that fit all available optical data can be demonstrated only for oxygen abundances 12 + log (O/H) > 7.2 (>1/30 solar) and values 0.6 dex larger are possible, depending on the assumed C/O abundance ratio. Plausible variations in the geometry of the nebula, the primary stellar continuum and the atomic data do not alter this conclusion. The C/O ratio is less than 10 by number and Ne/O is at most solar. A satisfactory model for PN G135 can be obtained in which elemental abundances are nearly the same as those of a new detailed model for K 648, the prototypical GHPN in the old globular cluster M 15 (with 12 + log (O/H) = 7.58 ∼ 1/13 solar), although C/O may be smaller. Nonetheless, given the paucity of argon and iron in the nebula, PN G135 is likely to be a more extreme Population II object than K 648, reinforcing the idea of an endogenous origin for part of the oxygen in very metal-poor PNe. Assuming a standard H-burning post-Asymptotic Giant Branch evolution, timescale and spectroscopic considerations lead to an optimal solution, in which the distance to PN G135 is 8 kpc, the effective temperature of the nucleus slightly less than 1.3 × 10 5 K, its luminosity 1.4 × 10 37 erg s −1 , its mass 0.59 M , the age of the ionized shell 10 4 yrs, the ionized mass 0.05 M and the abundances by number (H:He:C:O:Ne) = (10 6 :81 500:90:30:4.5), with C/H being rather an upper limit and O/H and Ne/H uncertain by ±0.3 and ±0.1 dex respectively. Line intensities that could be used as diagnostics of the nebular elemental abundances are provided. Detailed imaging together with ultraviolet and very deep far-red spectra of PN G135 will be essential to definitely narrow the range of acceptable parameters and help us decide whether this exceptional PN is so oxygen-poor as to possibly influence current views on stellar evolution.

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The surface carbon and nitrogen abundances in models of ultra metal-poor stars

Cited by 33 publications

References 35 publications

Low‐temperature primordial gas in merging halos

Low‐temperature primordial gas in merging halos

Low-Mass Extremely Metal-Poor Stellar Models: Yields, Uncertainties and the Galactic Halo Stars

Endogenous oxygen in the extremely metal-poor planetary nebula PN G135.9+55.9

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