Theoretical Evolution of Extremely Metal-Poor Stars

Wagner, R.

doi:10.1086/152952

Cited by 14 publications

(9 citation statements)

References 3 publications

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“…Discrepancies are greatest for isoleucine, serine, threonine and tryptophan where they exceed 10 %. The deduced composition corresponds to a molecular weight of 77770, a figure which includes 1900 for the glycan [13], which is close to the value of 76000 obtained long ago from the iron content of the diferric protein [14]. …”

supporting

confidence: 68%

The Primary Structure of Hen Ovotransferrin

Williams

Elleman

Kingston

et al. 1982

European Journal of Biochemistry

190

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Peptide sequences obtained from hen ovotransferrin are compared with the complete amino acid sequence of the protein deduced from a cDNA sequence (Jeltsch and Chambon, preceding paper). Of the 705 positions of the whole protein 605 can be matched by the peptide sequences. Some possible discrepancies between the two methods are pointed out. The two halves of the chain show marked similarities in their sequences with 37 identical residues. The positions of the 15 disulphide bridges are shown; there are 6 homologous bridges in each half of the molecule and 3 extra bridges which occur only in the C-terminal half. The terminal residues of the halfmolecule fragments obtained by limited proteolysis are identified. The two domains are joined by a 9-residue connecting peptide. Sequence variability has been found at 9 positions. The sequence of hen ovotransferrin IS compared with the partial sequence available for human transferrin. From this some tentative conclusions about the identities of the metal-binding residues and about the evolution of transferrin are reached.The iron-binding protein transferrin is present in all vertebrate species. The closely related protein lactoferrin (or lactotransferrin) appears to be restricted to mammals. The amino acid sequences of these proteins have been studied for many years in order to elucidate their structure, evolution and ironbinding properties. Brew and his colleagues [1,2] have determined about 80 % of the sequence of human serum transferrin and have discovered that the N-terminal and C-terminal halves of the chain have similar sequences, with about 40 identical residues. X-ray crystallography [3] and partial proteolysis experiments [4,5] show that each half of the chain folds up into a largely independent, compact domain which carries a specific metal-binding site. Since the domains can be isolated as single-chain fragments after partial proteolysis it can be inferred that the disulphide bridges are located within the domains, none passing between them. These data suggest that the present-day bilobar protein has evolved by gene duplication and subsequent fusion from a smaller ancestral protein, which apparently no longer exists. Partial sequence data on human lactoferrin show that this protein is homologous to transferrin and that it too possesses internal duplication of structure [6,7]. Lactoferrin may, thus, have arisen by a further duplication of the transferrin gene in the ancestors of the mammals.In birds expression of the transferrin gene in the oviduct, which is under steroid control, leads to the synthesis of ovotransferrin (conalbumin), which differs from serum transferrin only in the nature of the attached glycan [8,9]. The sequences of cysteic-acid-containing peptides from digests of performicacid-oxidized ovotransferrin have been determined [lo] ; 34 unique cysteic acid residues were identified and some of the disulphide bridges were characterized after pepsin digestion of the unoxidized protein. A 102-residue sequence, which includes the point of attachment of ...

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supporting

confidence: 68%

The Primary Structure of Hen Ovotransferrin

Williams

Elleman

Kingston

et al. 1982

European Journal of Biochemistry

190

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“…Numerical challenges aside, the exact boundary between survival and destruction for real stars is likely to be slightly different than what is predicted here, as the central densities of stars on the MS depend on rotation, metallicity, and age (Maeder 1974;Wagner 1974). Notably, our own Sun has a central density approximately twice that of the standard γ = 4/3 polytrope used to model it.…”

Section: The Boundary Between Survival or Destructionmentioning

confidence: 76%

Hydrodynamical Simulations to Determine the Feeding Rate of Black Holes by the Tidal Disruption of Stars: The Importance of the Impact Parameter and Stellar Structure

Guillochon

Ramírez-Ruiz

2013

ApJ

508

531

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The disruption of stars by supermassive black holes has been linked to more than a dozen flares in the cores of galaxies out to redshift z ∼ 0.4. Modeling these flares properly requires a prediction of the rate of mass return to the black hole after a disruption. Through hydrodynamical simulation, we show that aside from the full disruption of a solar mass star at the exact limit where the star is destroyed, the common assumptions used to estimateṀ (t), the rate of mass return to the black hole, are largely invalid. While the analytical approximation to tidal disruption predicts that the least-centrally concentrated stars and the deepest encounters should have more quickly-peaked flares, we find that the most-centrally concentrated stars have the quickest-peaking flares, and the trend between the time of peak and the impact parameter for deeply-penetrating encounters reverses beyond the critical distance at which the star is completely destroyed. We also show that the most-centrally concentrated stars produced a characteristic drop inṀ (t) shortly after peak when a star is only partially disrupted, with the power law index n being as extreme as -4 in the months immediately following the peak of a flare. Additionally, we find that n asymptotes to −2.2 for both low-and high-mass stars for approximately half of all stellar disruptions. Both of these results are significantly steeper than the typically assumed n = −5/3. As these precipitous decay rates are only seen for events in which a stellar core survives the disruption, they can be used to determine if an observed tidal disruption flare produced a surviving remnant. We provide fitting formulae for four fundamental quantities of tidal disruption as functions of the star's distance to the black hole at pericenter and its stellar structure: The total mass lost, the time of peak, the accretion rate at peak, and the power-law index shortly after peak. These results should be taken into consideration when flares arising from tidal disruptions are modeled.

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“…Models of hyper-metal-poor stars show that the location of the turnoff looses its sensitivity to the initial metal content for Z lower than Z % 10 À6 (Wagner 1974;Cassisi & Castellani 1993). That means that the T eff of the turnoff reaches a maximum value at ½Fe/ H % À4.…”

Section: New Irfm T Eff Scale For Halo Turnoff Stars Versus Stellar Ementioning

confidence: 99%

Permitted Oxygen Abundances and the Temperature Scale of Metal‐poor Turnoff Stars

Meléndez

Shchukina

Vasiljeva

et al. 2006

ApJ

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We use high-quality VLT/UVES published data of the permitted O i triplet and Fe ii lines to determine oxygen and iron abundances in unevolved (dwarfs, turnoff, subgiants) metal-poor halo stars. The calculations have been performed both in LTE and non-LTE (NLTE), employing effective temperatures obtained with the new infrared flux method (IRFM ) temperature scale by Ramírez & Meléndez, and surface gravities from Hipparcos parallaxes and theoretical isochrones. A new list of accurate transition probabilities for Fe ii lines, tied to the absolute scale defined by laboratory measurements, has been used. Interstellar absorption has been carefully taken into account by employing reddening maps, stellar energy distributions and Strömgren photometry. We find a plateau in the oxygento-iron ratio over more than 2 orders of magnitude in iron abundance (À3:2 < ½Fe/ H < À0:7), with a mean [O/ Fe ¼ 0:5 dex ( ¼ 0:1 dex), independent of metallicity, temperature, and surface gravity. The flat [O/ Fe] ratio is mainly due to the use of adequate NLTE corrections and the new IRFM temperature scale, which, for metal-poor F/early G dwarfs is hotter than most T eff scales used in previous studies of the O i triplet. According to the new IRFM T eff scale, the temperatures of turnoff halo stars strongly depend on metallicity, a result that is in excellent qualitative and quantitative agreement with stellar evolution calculations, which predict that the T eff of the turnoff at ½Fe/H ¼ À3 is about 600-700 K higher than that at ½Fe/H ¼ À1. Recent determinations of H temperatures in turnoff stars are in excellent relative agreement with the new IRFM T eff scale in the metallicity range À2:7 < ½Fe/H < À1, with a zero-point difference of only 61 K.

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Theoretical Evolution of Extremely Metal-Poor Stars

Cited by 14 publications

References 3 publications

The Primary Structure of Hen Ovotransferrin

The Primary Structure of Hen Ovotransferrin

Hydrodynamical Simulations to Determine the Feeding Rate of Black Holes by the Tidal Disruption of Stars: The Importance of the Impact Parameter and Stellar Structure

Permitted Oxygen Abundances and the Temperature Scale of Metal‐poor Turnoff Stars

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