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تسجيل مستخدم جديدDetailed abundances in a sample of very metal poor stars
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Unevolved metal poor stars are the witness of the early evolution of the Galaxy. The determination of their detailed chemical composition is an important tool to understand the chemical history of our Galaxy. The study of their chemical composition can also be used to constrain the nucleosynthesis of the first generation of supernovae that enriched the interstellar medium. The aim is to observe a sample of extremely metal poor stars (EMP stars) candidates selected from SDSS DR12 release and determine their chemical composition. We obtained high resolution spectra of a sample of five stars using HDS on Subaru telescope and used standard 1D models to compute the abundances. The stars we analysed have a metallicity [Fe/H] between -3.50 dex and -4.25 dex . We confirm that the five metal poor candidates selected from low resolution spectra are very metal poor. We present, the discovery of a new ultra metal-poor star (UMP star) with a metallicity of [Fe/H]= -4.25 dex (SDSS~J1050032.34$-$241009.7). We measured in this star an upper limit of lithium ( log(Li/H) <= 2.0. We found that the 4 most metal poor stars of our sample have a lower lithium abundance than the Spite plateau lithium value. We obtain upper limits for carbon in the sample of stars. None of them belong to the high carbon band. We measured abundances of Mg and Ca in most of the stars and found three new alpha-poor stars.
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We have obtained new detailed abundances of the Fe-group elements Sc through Zn (Z=21-30) in three very metal-poor ([Fe/H] $approx -3$) stars: BD 03 740, BD -13 3442 and CD -33 1173. High-resolution ultraviolet HST/STIS spectra in the wavelength rang
e 2300-3050AA were gathered, and complemented by an assortment of optical echelle spectra. The analysis featured recent laboratory atomic data for number of neutral and ionized species for all Fe-group elements except Cu and Zn. A detailed examination of scandium, titanium, and vanadium abundances in large-sample spectroscopic surveys indicates that they are positively correlated in stars with [Fe/H]<-$2. The abundances of these elements in BD 03 740, BD -13 3442 and CD -33 1173 and HD 84937. (studied in a previous paper of this series) are in accord with these trends and lie at the high end of the correlations. Six elements have detectable neutral and ionized features, and generally their abundances are in reasonable agreement. For Cr we find only minimal abundance disagreement between the neutral (mean of [Cri/Fe]=+0.01) and ionized species (mean of [Crii/Fe]=+0.08), unlike most studies in the past. The prominent exception is Co, for which the neutral species indicates a significant overabundance (mean of [Co/H]=-2.53), while no such enhancement is seen for the ionized species (mean of [Coii/H]=-2.93). These new stellar abundances, especially the correlations among Sc, Ti, and V, suggest that models of element production in early high-mass metal-poor stars should be revisited.
The light elements, Li, Be, and B, provide tracers for many aspects of astronomy including stellar structure, Galactic evolution, and cosmology. We have taken spectra of Be in 117 metal-poor stars ranging in metallicity from [Fe/H] = -0.5 to -3.5 wit
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Reconstructing the chemical evolution of the Milky Way is crucial for understanding the formation of stars, planets, and galaxies throughout cosmic time. Different studies associated with element production in the early universe and how elements are
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