scholarly journals The behaviour of lithium at high metallicity in the Milky Way. Selection effects in the samples and the possible role of atomic diffusion

2021 ◽  
Author(s):  
C. Charbonnel ◽  
S. Borisov ◽  
P. De Laverny ◽  
N. Prantzos
Keyword(s):  
Milky Way ◽  
Atomic Diffusion ◽  
Selection Effects ◽  
High Metallicity

scholarly journals Evolutionary catastrophes and the Goldilocks problem

2007 ◽  
Vol 6 (4) ◽  
pp. 325-329 ◽  
Author(s):  
Milan M. Ćirković
Keyword(s):  
Rare Earth ◽  
Milky Way ◽  
Human Life ◽  
Biological Evolution ◽  
Selection Effects ◽  
Mass Extinctions ◽  
Terrestrial Biosphere ◽  
Habitable Planet ◽  
Observation Selection

AbstractOne of the mainstays of the controversial ‘rare Earth’ hypothesis is the ‘Goldilocks problem’ regarding various parameters describing a habitable planet, partially involving the role of mass extinctions and other catastrophic processes in biological evolution. Usually, this is construed as support for the uniqueness of the Earth's biosphere and intelligent human life. Here it is argued that this is a misconstrual and that, on the contrary, observation-selection effects when applied to catastrophic processes make it very difficult for us to discern whether the terrestrial biosphere and evolutionary processes which created it are exceptional in the Milky Way or not. This agnosticism, in turn, supports the validity and significance of practical astrobiological and SETI research.

scholarly journals The role of faint population III supernovae in forming CEMP stars in ultra-faint dwarf galaxies

2021 ◽  
Author(s):  
Myoungwon Jeon ◽  
Volker Bromm ◽  
Gurtina Besla ◽  
Jinmi Yoon ◽  
Yumi Choi
Keyword(s):  
Milky Way ◽  
Dwarf Galaxies ◽  
Mass Resolution ◽  
Explosion Energy ◽  
High Carbon ◽  
Cosmological Simulations ◽  
Carbon Abundance ◽  
The Absolute ◽  
Zoom In

Abstract CEMP-no stars, a subset of carbon enhanced metal poor (CEMP) stars ($\rm [C/Fe]\ge 0.7$ and $\rm [Fe/H]\lesssim -1$) have been discovered in ultra-faint dwarf (UFD) galaxies, with Mvir ≈ 108 M⊙ and M* ≈ 103 − 104 M⊙ at z = 0, as well as in the halo of the Milky Way (MW). These CEMP-no stars are local fossils that may reflect the properties of the first (Pop III) and second (Pop II) generation of stars. However, cosmological simulations have struggled to reproduce the observed level of carbon enhancement of the known CEMP-no stars. Here we present new cosmological hydrodynamic zoom-in simulations of isolated UFDs that achieve a gas mass resolution of mgas ≈ 60 M⊙. We include enrichment from Pop III faint supernovae (SNe), with ESN = 0.6 × 1051 erg, to understand the origin of CEMP-no stars. We confirm that Pop III and Pop II stars are mainly responsible for the formation of CEMP and C-normal stars respectively. New to this study, we find that a majority of CEMP-no stars in the observed UFDs and the MW halo can be explained by Pop III SNe with normal explosion energy (ESN = 1.2 × 1051 erg) and Pop II enrichment, but faint SNe might also be needed to produce CEMP-no stars with $\rm [C/Fe]\gtrsim 2$, corresponding to the absolute carbon abundance of $\rm A(C)\gtrsim 6.0$. Furthermore, we find that while we create CEMP-no stars with high carbon ratio $\rm [C/Fe]\approx 3-4$, by adopting faint SNe, it is still challenging to reproduce CEMP-no stars with extreme level of carbon abundance of $\rm A(C)\approx 7.0-7.5$, observed both in the MW halo and UFDs.

The role of complementarity and selection effects in P acquisition of intercropping systems

2017 ◽  
Vol 422 (1-2) ◽  
pp. 479-493 ◽  
Author(s):  
Xiao-Fei Li ◽  
Cheng-Bao Wang ◽  
Wei-Ping Zhang ◽  
Le-Hua Wang ◽  
Xiu-Li Tian ◽  
...  
Keyword(s):  
Selection Effects ◽  
P Acquisition

On the Role of Surface Diffusion in Stress Relaxation During Electromigration

1995 ◽  
Vol 391 ◽  
Author(s):  
L.M. Klinger ◽  
L. Levin ◽  
E.E. Glickman
Keyword(s):  
Stress Relaxation ◽  
Surface Diffusion ◽  
Hydrostatic Stress ◽  
Stress Gradient ◽  
Film Surface ◽  
Diffusional Creep ◽  
Atomic Diffusion ◽  
Material Transport ◽  
Diffusional Flux

AbstractWe report on the role of surface diffusion involved in relaxation of electromigration (EM) induced compressive stresses in relation to hillock growth and EM behavior of interconnects. Two competing mechanisms of EM stress relaxation by material transport onto the surface are considered. The first is hillocking by threshold diffusional creep (TCH), with rather large blocks of material (grains or group of grains) involved in plastic flow. The second mechanism, atomic diffusion hillocking (ADH), is presumed to be a nonthreshold one, and represents atomic grain boundary (GB) diffusion stimulated by the hydrostatic stress gradient in the direction normal to the film surface. The latter process involves surface diffusion because GB diffusional flux onto the surface must be coupled with the flux of redistribution of the atoms over the surface. If ADH acts rapidly, this should prevent the build-up of the matter at the down-wind (anode) end of the stripe, and thus, eliminate the Blech EM threshold resulting from the stress-gradient along the stripe. The question as to whether GB diffusion capable of transporting atoms pushed by electron wind along the stripe is also effective in relieving compressive stress by GB migration of the surplus atoms in the normal direction, has remained open up to now. The problem is especially acute for short or/and narrow lines separated into short polycrystalline segments, where the Blech threshold effects are critical to EM reliability.We derived the main features of the EM behavior in drift velocity test geometry assuming that both TCH and ADH are operative. The result can be compared with available and future experimental observations in order to reveal if and when the ADH mechanism with surface diffusion involved works.

scholarly journals Local Stellar Kinematics from RAVE data—VII. Metallicity Gradients from Red Clump Stars

2016 ◽  
Vol 33 ◽  
Author(s):  
Ö. Önal Taş ◽  
S. Bilir ◽  
G. M. Seabroke ◽  
S. Karaali ◽  
S. Ak ◽  
...  
Keyword(s):  
Radial Velocity ◽  
Milky Way ◽  
Absolute Magnitude ◽  
Selection Effects ◽  
Stellar Kinematics ◽  
Experiment Data ◽  
Radial Gradient ◽  
Data Release ◽  
The Difference ◽  
Red Clump

AbstractWe investigate the Milky Way Galaxy’s radial and vertical metallicity gradients using a sample of 47 406 red clump stars from the RAdial Velocity Experiment Data Release 4. Distances are calculated by adopting Ks-band absolute magnitude as −1.54±0.04 mag for the sample. The metallicity gradients are calculated with their current orbital positions (Rgc and Z) and with their orbital properties (Rm and zmax): d[Fe/H]/dRgc = −0.047±0.003 dex kpc−1 for |Z| ≤ 0.5 kpc and d[Fe/H]/dRm = −0.025±0.002 dex kpc−1 for zmax ≤ 0.5 kpc. This reaffirms the radial metallicity gradient in the thin disc but highlights that gradients are sensitive to the selection effects caused by the difference between Rgc and Rm. The radial gradient is flat in the distance interval 0.5-1 kpc from the plane and then becomes positive greater than 1 kpc from the plane. The radial metallicity gradients are also eccentricity dependent. We showed that d[Fe/H]/dRm = −0.089±0.010, −0.073±0.007, −0.053±0.004 and −0.044±0.002 dex kpc−1 for ep ≤ 0.05, ep ≤ 0.07, ep ≤ 0.10 and ep ≤ 0.20 sub-samples, respectively, in the distance interval zmax ≤ 0.5 kpc. Similar trend is found for vertical metallicity gradients. Both the radial and vertical metallicity gradients are found to become shallower as the eccentricity of the sample increases. These findings can be used to constrain different formation scenarios of the thick and thin discs.

scholarly journals The WAGGS project-III. Discrepant mass-to-light ratios of Galactic globular clusters at high metallicity

2020 ◽  
Vol 492 (3) ◽  
pp. 3859-3871 ◽  
Author(s):  
H Dalgleish ◽  
S Kamann ◽  
C Usher ◽  
H Baumgardt ◽  
N Bastian ◽  
...  
Keyword(s):  
Globular Clusters ◽  
Stellar Population ◽  
Milky Way ◽  
Population Models ◽  
Theoretical Predictions ◽  
Field Unit ◽  
Stellar Masses ◽  
Kinematic Information ◽  
High Metallicity ◽  
Integral Field

ABSTRACT Observed mass-to-light ratios (M/L) of metal-rich globular clusters (GCs) disagree with theoretical predictions. This discrepancy is of fundamental importance since stellar population models provide the stellar masses that underpin most of extragalactic astronomy, near and far. We have derived radial velocities for 1622 stars located in the centres of 59 Milky Way GCs – 12 of which have no previous kinematic information – using integral-field unit data from the WAGGS project. Using N-body models, we determine dynamical masses and M/LV for the studied clusters. Our sample includes NGC 6528 and NGC 6553, which extend the metallicity range of GCs with measured M/L up to [Fe/H] ∼ −0.1 dex. We find that metal-rich clusters have M/LV more than two times lower than what is predicted by simple stellar population models. This confirms that the discrepant M/L–[Fe/H] relation remains a serious concern. We explore how our findings relate to previous observations, and the potential causes for the divergence, which we conclude is most likely due to dynamical effects.

scholarly journals Multi-Wavelength Surveys for Galaxies Hidden by the Milky Way

1999 ◽  
Vol 171 ◽  
pp. 103-110 ◽  
Author(s):  
Renée C. Kraan-Korteweg
Keyword(s):  
Near Infrared ◽  
Milky Way ◽  
Status Report ◽  
Selection Effects ◽  
Systematic Mapping ◽  
Local Universe ◽  
First Results ◽  
Multi Wavelength ◽  
Zone Of Avoidance

AbstractThe systematic mapping of obscured and optically invisible galaxies behind the Milky Way through complementary surveys are important in arriving at the whole-sky distribution of complete galaxy samples and therewith for our understanding of the dynamics in the local Universe. In this paper, a status report is given of the various deep optical, near infrared (NIR), and systematic blind H I-surveys in the Zone of Avoidance, including a discussion on the limitations and selection effects inherent to the different multi-wavelength surveys and first results.

scholarly journals Molecular-scale investigation of the oxidation behavior of chromia-forming alloys in high-temperature CO2

2021 ◽  
Vol 5 (1) ◽  
Author(s):  
Richard P. Oleksak ◽  
Rafik Addou ◽  
Bharat Gwalani ◽  
John P. Baltrus ◽  
Tao Liu ◽  
...  
Keyword(s):  
High Temperature ◽  
Power Systems ◽  
High Purity ◽  
Photoelectron Spectroscopy ◽  
Ambient Pressure ◽  
Critical Role ◽  
Atomic Scale ◽  
Atomic Diffusion ◽  
Carbon Transport

AbstractCurrent and future power systems require chromia-forming alloys compatible with high-temperature CO2. Important questions concerning the mechanisms of oxidation and carburization remain unanswered. Herein we shed light onto these processes by studying the very initial stages of oxidation of Fe22Cr and Fe22Ni22Cr model alloys. Ambient-pressure X-ray photoelectron spectroscopy enabled in situ analysis of the oxidizing surface under 1 mbar of flowing CO2 at temperatures up to 530 °C, while postexposure analyses revealed the structure and composition of the oxidized surface at the near-atomic scale. We found that gas purity played a critical role in the kinetics of the reaction, where high purity CO2 promoted the deposition of carbon and the selective oxidation of Cr. In contrast, no carbon deposition occurred in low purity CO2 and Fe oxidation ensued, thus highlighting the critical role of impurities in defining the early oxidation pathway of the alloy. The Cr-rich oxide formed on Fe22Cr in high purity CO2 was both thicker and more permeable to carbon compared to that formed on Fe22Ni22Cr, where carbon transport appeared to occur by atomic diffusion through the oxide. Alternatively, the Fe-rich oxide formed in low purity CO2 suggested carbon transport by molecular CO2.

scholarly journals A Sober Look at Bars in Galaxies

1996 ◽  
Vol 157 ◽  
pp. 560-568
Author(s):  
William C. Keel
Keyword(s):  
Star Formation ◽  
Milky Way ◽  
Nuclear Activity ◽  
Secular Evolution ◽  
Key Issues

AbstractI review some of the more notable observational aspects of bars in galaxies. Key issues include the overall occurrence of bars, secular evolution of bars and bulges, the differences in bar properties with Hubble type, the role of bars in star formation and nuclear activity, and the evidence for a bar at the center of the Milky Way. These lead to a “wish list” of future observations.

scholarly journals Simulations of a Population of Planetary Nebulae

1993 ◽  
Vol 155 ◽  
pp. 461-464
Author(s):  
G. Stasinska ◽  
R. Tylenda
Keyword(s):  
Planetary Nebulae ◽  
Selection Effects ◽  
Galactic Bulge ◽  
Radio Observations

We present a simulation of the population of Galactic bulge planetary nebulae (GBPN), which matches the diagrams obtained from VLA radio observations. This simulation may not be the only one fitting the observed data, but it helps understanding the role of observational uncertainties and selection effects in the interpretation of observational diagrams.

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