اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدG112-43/44: A metal-poor binary star with a unique chemical composition and kinematics like the Helmi streams
53
0
0.0
(
0
)
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
G112-43/44, alias BD+00_2058 A and B, is a metal-poor ([Fe/H] = -1.3) wide-orbit binary star with extreme kinematics. We use high-precision determinations of the chemical compositions of 94 metal-poor dwarf stars in the solar neighbourhood to compare abundance ratios for G112-43/44 with ratios for stars having similar metallicity taking into account the effect of deviations from local thermodynamic equilibrium on the derived abundances, and Gaia EDR3 data are used to compare the kinematics. The abundances of the two components of G112-43/44 agree within 0.05 dex for nearly all elements, but there is a hint of a correlation of the difference in [X/H] with elemental condensation temperature, which may be due to planet-star interactions. The Mg/Fe, Si/Fe, Ca/Fe, and Ti/Fe ratios of G112-43/44 agree with the corresponding ratios for accreted (Gaia-Enceladus) stars, but Mn/Fe, Ni/Fe, Cu/Fe, and Zn/Fe are significantly enhanced. The kinematics show that G112-43/44 belongs to the Helmi streams in the solar neighbourhood and in view of this, we discuss if the abundance peculiarities of G112-43/44 can be explained by chemical enrichment from supernovae events in the progenitor dwarf galaxy of the Helmi streams. Interestingly, yields calculated for a helium shell detonation Type Ia supernova model can explain the enhancement of Mn/Fe, Ni/Fe, Cu/Fe, and Zn/Fe in G112-43/44 and three other alpha-poor stars in the Galactic halo, one of which have Helmi streams kinematics. The helium shell detonation model predicts, however, also enhanced abundance ratios of Ca/Fe, Ti/Fe, and Cr/Fe in disagreement with the observed ratios.
قيم البحث
اقرأ أيضاً
We present detailed chemical abundances for the bright carbon-enhanced metal-poor (CEMP) star BD+44 493, previously reported on by Ito et al. Our measurements confirm that BD+44 493 is an extremely metal-poor ([Fe/H]=-3.8) subgiant star with excesses
of carbon and oxygen. No significant excesses are found for nitrogen and neutron-capture elements (the latter of which place it in the CEMP-no class of stars). Other elements that we measure exhibit abundance patterns that are typical for non-CEMP extremely metal-poor stars. No evidence for variations of radial velocity have been found for this star. These results strongly suggest that the carbon enhancement in BD+44 493 is unlikely to have been produced by a companion asymptotic giant-branch star and transferred to the presently observed star, nor by pollution of its natal molecular cloud by rapidly-rotating, massive, mega metal-poor ([Fe/H] < -6.0) stars. A more likely possibility is that this star formed from gas polluted by the elements produced in a faint supernova, which underwent mixing and fallback, and only ejected small amounts of elements of metals beyond the lighter elements. The Li abundance of BD+44 493 (A(Li)=log(Li/H)+12=1.0) is lower than the Spite plateau value, as found in other metal-poor subgiants. The upper limit on Be abundance (A(Be)=log(Be/H)+12<-1.8) is as low as those found for stars with similarly extremely-low metallicity, indicating that the progenitors of carbon- (and oxygen-) enhanced stars are not significant sources of Be, or that Be is depleted in metal-poor subgiants with effective temperatures of ~5400K.
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
incorporated into gas and stars are necessary to piece together how the elements evolved. These include establishing chemical abundance trends, as set by metal-poor stars, comparing nucleosynthesis yield predictions with stellar abundance data, and theoretical modeling of chemical evolution. To aid these studies, we have collected chemical abundance measurements and other information such as stellar parameters, coordinates, magnitudes, and radial velocities, for extremely metal-poor stars from the literature. The database, JINAbase, contains 1658 unique stars, 60% of which have [Fe/H]<2.5. This information is stored in an SQL database, together with a user-friendly queryable web application (http://jinabase.pythonanywhere.com). Objects with unique chemical element signatures (e.g., r-process stars, s-process and CEMP stars) are labeled or can be classified as such. The web application enables fast selection of customized comparison samples from the literature for the aforementioned studies and many more. Using the multiple entries for three of the most well studied metal-poor stars, we evaluate systematic uncertainties of chemical abundances measurements. We provide a brief guide on the selection of chemical elements for model comparisons for non- spectroscopists who wish to learn about metal-poor stars and the details of chemical abundances measurements.
Atmospheric parameters and chemical compositions for ten stars with metallicities in the region of -2.2< [Fe/H] <-0.6 were precisely determined using high resolution, high signal to noise, spectra. For each star the abundances, for 14 to 27 elements,
were derived using both LTE and NLTE approaches. In particular, differences by assuming LTE or NLTE are about 0.10 dex; depending on [Fe/H], Teff, gravity and element lines used in the analysis. We find that the O abundance has the largest error, ranging from 0.10 and 0.2 dex. The best measured elements are Cr, Fe, and Mn; with errors etween 0.03 and 0.11 dex. The stars in our sample were included in previous different observational work. We provide a consistent data analysis. The data dispersion introduced in the literature by different techniques and assumptions used by the different authors is within the observational errors, excepting for HD103095. We compare these results with stellar observations from different data sets and a number of theoretical galactic chemical evolution (GCE) simulations. We find a large scatter in the GCE results, used to study the origin of the elements. Within this scatter as found in previous GCE simulations, we cannot reproduce the evolution of the elemental ratios [Sc/Fe], [Ti/Fe], and [V/Fe] at different metallicities. The stellar yields from core collapse supernovae (CCSN) are likely primarily responsible for this discrepancy. Possible solutions and open problems are discussed.
Molecular absorption lines of OH (99 lines) and CH (105 lines) are measured for the carbon-enhanced metal-poor star BD+44 493 with [Fe/H]=-3.8. The abundances of oxygen and carbon determined from individual lines based on an 1D-LTE analysis exhibit s
ignificant dependence on excitation potentials of the lines; d log e/d chi ~ -0.15 - -0.2 dex/eV, where e and chi are elemental abundances from individual spectral lines and their excitation potentials, respectively. The dependence is not explained by the uncertainties of stellar parameters, but suggests that the atmosphere of this object possesses a cool layer that is not reproduced by the 1D model atmosphere. This result agrees with the predictions by 3D model calculations. Although absorption lines of neutral iron exhibit similar trend, it is much weaker than found in molecular lines and that predicted by 3D LTE models.
We present the first time abundance analysis of a very metal-poor carbon-enhanced star CD-27 14351 based on a high resolution (R ~ 48000) FEROS spectrum. Our abundance analysis performed using Local Thermodynamic Equilibrium (LTE) model atmospheres s
hows that the object is a cool star with stellar atmospheric parameters, effective temperature Teff = 4335 K, surface gravity log g = 0.5, microturbulence = 2.42 km/s, and, metallicity [Fe/H] = -2.6. The star exhibits high carbon and nitrogen abundances with [C/Fe] = 2.89 and [N/Fe] = 1.89. Overabundances of neutron-capture elements are evident in Ba, La, Ce, and Nd with estimated [X/Fe] > 1, the largest enhancement being seen in Ce with [Ce/Fe] = 2.63. While the first peak s-process elements Sr and Y are found to be enhanced with respect to Fe, ([Sr/Fe] = 1.73 and [Y/Fe] = 1.91) the third peak s-process element Pb could not be detected in our spectrum at the given resolution. Europium, primarily a r-process element also shows an enhancement with [Eu/Fe] = 1.65. With [Ba/Eu] = 0.12 the object CD-27 14351 satisfies the classification criterion for CEMP-r/s star. The elemental abundance distributions observed in this star is discussed in light of chemical abundances observed in other CEMP stars from literature.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
