Metal-Poor Halo Stars as Tracers of ISM Mixing Processes During Halo Formation

Argast, D.; Samland, M.; Gerhard, Ortwin; Thielemann, Friedrich‐Karl

doi:10.1007/10719504_35

Cited by 9 publications

(15 citation statements)

References 48 publications

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“…The formulas given in [6] agree with the expressions of [7] for m = (0.2…6)m ᭪ , the expressions of [41] for m = (0.6…3)m ᭪ , and the expressions of [12] for m = (1.5…6)m ᭪ . The tabulated values of [40] also cor respond to the formulas of [6] for (0.7…1.4)m ᭪ .…”

Section: Introductionsupporting

confidence: 70%

“…In the mass range from 6m ᭪ to 40m ᭪ , the H time-mass relationship given in [7] yields systematically exaggerated lifetimes for stars on the main sequence; for masses higher than 63m ᭪ , this relationship cannot be used (the approximating polynomial has a minimum for a mass of 63m ᭪ ). For masses higher than 100m ᭪ , this relationship yields the H time that is higher than in [6] but lower than that calculated using the formulas of [12,41]. The analysis of stellar models with only solar elemental composition does not allow us to single out preferred relationships for H times as functions of stellar masses starting with 6m ᭪ and higher.…”

Section: Introductionmentioning

confidence: 85%

“…The H time-mass relationships [12,40,41] calculated for the mass range (0.8…120)m ᭪ agree with each other within 10%, hindering the unambiguous choice of one of them. These results do not include H times for red dwarfs with masses lower than 0.6m ᭪ and metallicities of Z = 0 and Z = Z ᭪ .…”

Section: Zakhozhaymentioning

confidence: 99%

“…As can be seen in the above mentioned review, the H times for the stars with masses of m > (0.6…1)m ᭪ are generalized for Z = Z ᭪ in the form of analytical expressions in [3,6,7,12,41] and tabulated in [40], KINEMATICS while those for the stars with Z = 0 are only tabulated [35,36,42,47]. There is proposed only one H timemass relationship for stars of the lowest masses [8]: (1) where τ H is the H time in years and M is the stellar mass in solar masses, b 0 = 10 10 , and b 1 = 3…4.…”

Section: General Expressions For Approximating the H Time-mass Relatimentioning

confidence: 99%

“…Based on these results, new "H time-mass" relationships were derived for the mass ranges (0.6…120)m ᭪ , (0.8…120)m ᭪ , and Z = 0.00007…0.03, 0.0004…0.05 in [41] and [12], respectively. The H times for masses of (0.6…120)m ᭪ and Z = 0.0004…0.05 are also tabulated in [40].The H time-mass relationships [12,40,41] calculated for the mass range (0.8…120)m ᭪ agree with each other within 10%, hindering the unambiguous choice of one of them. These results do not include H times for red dwarfs with masses lower than 0.6m ᭪ and metallicities of Z = 0 and Z = Z ᭪ .…”

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confidence: 99%

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Lifetimes of stars in the main sequence and the maximum mass of stars in the galactic disk

Zakhozhay

2013

Kinemat. Phys. Celest. Bodies

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Generalized and interconsistent approximation formulas are derived to describe the rela tionship between the hydrogen burning time and the zero age stellar mass for the mass and elemental composition ranges characteristic of stars that have been formed during the lifetime of the universe. The maximum masses of population I stars are estimated based on the known statistical relationships among stellar characteristics that agree with observational data. ZAKHOZHAYfor H times were given in [7] (for the solar elemental composition and masses of (0.2…100)m ᭪ , and higher than 100m ᭪ ) and in [3] (for masses of (1…100)m ᭪ , regardless of elemental composition).New numerical stellar models were obtained by Padova [10,15,16,[19][20][21] and GSEN [18,[43][44][45] teams in the 1990s. Based on these results, new "H time-mass" relationships were derived for the mass ranges (0.6…120)m ᭪ , (0.8…120)m ᭪ , and Z = 0.00007…0.03, 0.0004…0.05 in [41] and [12], respectively. The H times for masses of (0.6…120)m ᭪ and Z = 0.0004…0.05 are also tabulated in [40].The H time-mass relationships [12,40,41] calculated for the mass range (0.8…120)m ᭪ agree with each other within 10%, hindering the unambiguous choice of one of them. These results do not include H times for red dwarfs with masses lower than 0.6m ᭪ and metallicities of Z = 0 and Z = Z ᭪ . The cited papers provide expressions for the free terms a i (Z) that are functions of heavy nucleus abundances and cannot be used for our purposes. For Z =0, the values of coefficients in the free terms derived in [12] require a special anal ysis to ensure whether or not these correspond to the results of numerical modeling of zero metallicity stars [35,36,42,47], while those obtained in [41] approach infinity. Moreover, when the a i (Z) coefficients are used for masses of m > 100m ᭪ , the H times begin to increase, which contradicts the physical meaning.

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Section: Introductionsupporting

confidence: 70%

Section: Introductionmentioning

confidence: 85%

Section: Zakhozhaymentioning

confidence: 99%

Section: General Expressions For Approximating the H Time-mass Relatimentioning

confidence: 99%

mentioning

confidence: 99%

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Lifetimes of stars in the main sequence and the maximum mass of stars in the galactic disk

Zakhozhay

2013

Kinemat. Phys. Celest. Bodies

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High-precision stellar abundances of the elements: methods and applications

Nissen

Gustafsson

2018

Astron Astrophys Rev

102

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Efficient spectrographs at large telescopes have made it possible to obtain high-resolution spectra of stars with high signal-to-noise ratio and advances in model atmosphere analyses have enabled estimates of high-precision differential abundances of the elements from these spectra, i.e. with errors in the range 0.01 -0.03 dex for F, G, and K stars.Methods to determine such high-precision abundances together with precise values of effective temperatures and surface gravities from equivalent widths of spectral lines or by spectrum synthesis techniques are outlined, and effects on abundance determinations from using a 3D non-LTE analysis instead of a classical 1D LTE analysis are considered.The determination of high-precision stellar abundances of the elements have led to the discovery of unexpected phenomena and relations with important bearings on the astrophysics of galaxies, stars, and planets, i.e. i) Existence of discrete stellar populations within each of the main Galactic components (disk, halo, and bulge) providing new constraints on models for the formation of the Milky Way. ii) Differences in the relation between abundances and elemental condensation temperature for the Sun and solar twins suggesting dust-cleansing effects in proto-planetary disks and/or engulfment of planets by stars; iii) Differences in chemical composition between binary star components and between members of open or globular clusters showing that star-and cluster-formation processes are more complicated than previously thought; iv) Tight relations between some abundance ratios and age for solar-like stars providing new constraints on nucleosynthesis and Galactic chemical evolution models as well as the composition of terrestrial exoplanets.We conclude that if stellar abundances with precisions of 0.01 -0.03 dex can be achieved in studies of more distant stars and stars on the giant and supergiant branches, many more interesting future applications, of great relevance to stellar and galaxy evolution, are probable. Hence, in planning abundance surveys, it is important to carefully balance the need for large samples of stars against the spectral resolution and signal-to-noise ratio needed to obtain high-precision abundances. Furthermore, it is an advantage to work differentially on stars with similar atmospheric parameters, because then a simple 1D LTE analysis of stellar spectra may be sufficient. However, when determining high-precision absolute abundances or differential abundance between stars having more widely different parameters, e.g. metal-poor stars compared to the Sun or giants to dwarfs, then 3D non-LTE effects must be taken into account.

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