scholarly journals Constraints on stellar rotation from the evolution of Sr and Ba in the Galactic halo

2021 ◽  
Vol 502 (2) ◽  
pp. 2495-2507
Author(s):  
F Rizzuti ◽  
G Cescutti ◽  
F Matteucci ◽  
A Chieffi ◽  
R Hirschi ◽  
...  
Keyword(s):  
Chemical Evolution ◽  
Galactic Halo ◽  
Massive Stars ◽  
Rotational Behaviour ◽  
Model Data ◽  
Stellar Rotation ◽  
Data Comparison ◽  
Promising Tool ◽  
The Galaxy ◽  
The Mean

ABSTRACT Recent studies show that the chemical evolution of Sr and Ba in the Galaxy can be explained if different production sites, hosting r- and s-processes, are taken into account. However, the question of unambiguously identifying these sites is still unsolved. Massive stars are shown to play an important role in the production of s-material if rotation is considered. In this work, we study in detail the contribution of rotating massive stars to the production of Sr and Ba, in order to explain their chemical evolution, but also to constrain the rotational behaviour of massive stars. A stochastic chemical evolution model was employed to reproduce the enrichment of the Galactic halo. We developed new methods for model-data comparison which help to objectively compare the stochastic results to the observations. We employed these methods to estimate the value of free parameters which describe the rotation of massive stars, assumed to be dependent on the stellar metallicity. We constrain the parameters using the observations for Sr and Ba. Employing these parameters for rotating massive stars in our stochastic model, we are able to correctly reproduce the chemical evolution of Sr and Ba, but also Y, Zr, and La. The data supports a decrease of both the mean rotational velocities and their dispersion with increasing metallicity. Our results show that a metallicity-dependent rotation is a necessary assumption to explain the s-process in massive stars. Our novel methods of model-data comparison represent a promising tool for future galactic chemical evolution studies.

scholarly journals Nitrogen evolution in the halo, thick disc, thin disc, and bulge of the Galaxy

2021 ◽  
Vol 508 (1) ◽  
pp. 719-727
Author(s):  
V Grisoni ◽  
F Matteucci ◽  
D Romano
Keyword(s):  
Galactic Halo ◽  
Massive Stars ◽  
Chemical Elements ◽  
Distribution Functions ◽  
Abundance Pattern ◽  
Origin And Evolution ◽  
Thick Disc ◽  
Thin Disc ◽  
Abundance Patterns ◽  
The Galaxy

ABSTRACT We study the evolution of nitrogen (N) in the Galactic halo, thick disc, thin disc, and bulge by comparing detailed chemical evolution models with recent observations. The models used in this work have already been constrained to explain the abundance patterns of α-elements and the metallicity distribution functions of halo, disc, and bulge stars; here, we adopt them to investigate the origin and evolution of N in the different Galactic components. First, we consider different sets of yields and study the importance of the various channels proposed for N production. Secondly, we apply the reference models to study the evolution of both the Galactic discs and bulge. We conclude that: i) primary N produced by rotating massive stars is required to reproduce the plateau in log(N/O) and [N/Fe] ratios at low metallicity, as well as the secondary and primary production from low- and intermediate-mass stars to reproduce the data of the thin disc; ii) the parallel model can provide a good explanation of the evolution of N abundance in the thick and thin discs, and we confirm that the thick disc has evolved much faster than the thin disc, in agreement with the results from the abundance patterns of other chemical elements; and iii) finally, we present new model predictions for N evolution in the Galactic bulge, and we show that the observations in bulge stars can be explained if massive stars rotate fast during the earliest phases of Galactic evolution, in agreement with findings from the abundance pattern of carbon.

scholarly journals Chemical Evolution of the Galactic Disk and the Radial Metallicity Gradient

1976 ◽  
Vol 72 ◽  
pp. 207-208
Author(s):  
M. Mayor
Keyword(s):  
Chemical Evolution ◽  
Galactic Disk ◽  
Sodium Concentration ◽  
Mean Value ◽  
Heavy Elements ◽  
Solar Neighbourhood ◽  
Chemical Gradient ◽  
The Galaxy ◽  
The Mean ◽  
Image Position

An analysis of the kinematical and photometric properties of about 600dF stars and 600 gG-gK stars permits the estimation of the radial chemical gradient in the Galaxy. The mean value in the solar neighbourhood obtained for all of these stars is: The values of [Fe/H] used for this estimation are deduced for the dF stars using uvby β photometric measurements and for the gG-gK stars from a list published by Hansen and Kjaergaard. An estimate of the chemical gradient using UBV photometry of dG stars in the solar neighbourhood gives a similar value. For all the samples studied (dF, dG or giants) the order of magnitude for the gradient is the same. However, for the youngest stars in these samples the metallicity gradient could be larger: Such a value may be affected by dynamical perturbations of the galactic disk.The values published by Hansen and Kjaergaard for the sodium concentration in giant star atmospheres also indicate a radial galactic gradient of the same order.If only the dF stars which are sufficiently evolved to allow an age estimate are considered, then a very distinct correlation is found between age and metallicity: An important fraction of the heavy elements actually present in the solar neighbourhood seems to have synthetized during the life of the galactic disk.The two derivatives and are not independent, but are connected by the chemical evolution of the galactic disk. Some elementary deductions show the coherency of these two estimates.The intrinsic dispersion of metallicities, at a given age and birthplace, is somewhat lower than the admitted values. It has not been possible to find any significant variation with age of this quantity from the present observational material. The simultaneous variation of σ2w and [Fe/H] as function of age is evidence for a z stratification in the mean abundance of the heavy elements. The ratio between the mean metallicity in the plane and at z = 500 pc is estimated to be about a factor of two.Finally it is shown that the interpretation of the kinematical diagrams for different groups of given metallicity is ambiguous. A relation as e vs [Fe/H] depends not only on the chemical and kinematical history of the Galaxy but is also strongly dependent on the observational errors of [Fe/H] and on criteria used to define the sample.A paper containing the above results has been submitted for publication in Astronomy and Astrophysics.

scholarly journals New Beryllium results in halo stars from Keck/HIRES spectra

2009 ◽  
Vol 5 (S268) ◽  
pp. 231-236
Author(s):  
Ann Merchant Boesgaard ◽  
Jeffrey A. Rich ◽  
Emily M. Levesque ◽  
Brendan P. Bowler
Keyword(s):  
Galactic Halo ◽  
Massive Stars ◽  
High Energy ◽  
High Signal ◽  
Signal To Noise ◽  
Interstellar Gas ◽  
Halo Stars ◽  
Spallation Reactions ◽  
Blue Straggler ◽  
The Galaxy

AbstractWe have obtained high-resolution, high signal-to-noise Keck spectra to determine Be abundances in over 100 stars in the Galactic halo. The stellar metallicities range from [Fe/H] = −0.50 to −3.50. Using this large sample, we have examined the trends of Be with Fe and Be with O. We find a real dispersion in Be at a given [O/H] that indicates that Be may not be a good cosmochronometer. Our results indicate that the dominant production mechanism for Be changes as the Galaxy ages. In the early eras of the Galaxy, when massive stars become supernovae, Be is produced from the acceleration of energetic CNO atoms which bombard protons in the vicinity of supernovae. Later spallation reactions occur as high energy protons bombard CNO atoms in the interstellar gas. The change occurs near [Fe/H] = −2.2. We have found that Be is deficient in Li-deficient halo stars, which favors the blue straggler analog hypothesis.

scholarly journals EMP stars with high mass IMF and hierarchical galaxy formation

2009 ◽  
Vol 5 (S265) ◽  
pp. 128-129
Author(s):  
Yutaka Komiya ◽  
Takuma Suda ◽  
Asao Habe ◽  
Masayuki Y. Fujimoto
Keyword(s):  
Chemical Evolution ◽  
Galaxy Formation ◽  
Galactic Halo ◽  
Early Stage ◽  
Mass Function ◽  
Initial Mass Function ◽  
High Mass ◽  
Halo Stars ◽  
The Galaxy ◽  
Metallicity Distribution

AbstractExtremely metal-poor (EMP) stars in the Galactic halo are stars formed in the very early stage of the chemical evolution of the Galaxy. In previous study, we proposed that typical mass of EMP stars are massive, based on observations of carbon-enhanced EMP stars. In this study, we build a merger tree of the Galaxy semi-analytically and follow the chemical evolution along the merger tree. We also consider the effect of binary and high-mass initial mass function(IMF). Resultant theoretical metallicity distribution function (MDF) and abundance distribution are compared with observed metal-poor halo stars.

Lifting the Veil on Ultra Metal-Poor Stars in the Outermost Halo

2017 ◽  
Vol 13 (S334) ◽  
pp. 389-390
Author(s):  
Jinmi Yoon ◽  
Devin D. Whitten ◽  
Timothy C. Beers ◽  
Vinicius M. Placco ◽  
Young Sun Lee ◽  
...  
Keyword(s):  
Early Universe ◽  
Chemical Evolution ◽  
Galactic Halo ◽  
Mass Function ◽  
Initial Mass Function ◽  
Theoretical Studies ◽  
The Past ◽  
Large Numbers ◽  
The Galaxy ◽  
The Veil

AbstractThe study of extremely metal-poor (EMP; [Fe/H] <−3.0) and ultra metal-poor (UMP; [Fe/H] <−4.0) stars is crucial for better understanding first-star nucleosynthesis and constraining the initial mass function in the early Universe. However, UMP stars discovered in the past 25 years only number ~25. A few recent theoretical studies have pointed out that there is likely to exist large numbers of EMP and UMP stars in the periphery of the Galactic halo, at distances exceeding 30-50 kpc. We present identifications of several new EMP/UMP stars and introduce a survey to expedite discovering hundreds to thousands of EMP/UMP stars in the outermost halo (as well as in the local volume) over the next few years, which could revolutionize chemical-evolution studies of the Galaxy.

scholarly journals Chemical evolution of star clusters

2010 ◽  
Vol 368 (1913) ◽  
pp. 801-828 ◽  
Author(s):  
Jacco Th. van Loon
Keyword(s):  
Dark Matter ◽  
Chemical Evolution ◽  
Gravitational Potential ◽  
Globular Clusters ◽  
Galactic Halo ◽  
Dwarf Galaxies ◽  
Star Clusters ◽  
Galactic Bulge ◽  
Potential Wells ◽  
The Galaxy

I discuss the chemical evolution of star clusters, with emphasis on old Galactic globular clusters (GCs), in relation to their formation histories. GCs are clearly formed in a complex fashion, under markedly different conditions from any younger clusters presently known. Those special conditions must be linked to the early formation epoch of the Galaxy and must not have occurred since. While a link to the formation of GCs in dwarf galaxies has been suggested, present-day dwarf galaxies are not representative of the gravitational potential wells within which the GCs formed. Instead, a formation deep within the proto-Galaxy or within dark-matter mini-haloes might be favoured. Not all GCs may have formed and evolved similarly. In particular, we may need to distinguish Galactic Halo from Galactic Bulge clusters.

scholarly journals The Chemical Evolution of the Galactic Halo and Disk

1987 ◽  
Vol 115 ◽  
pp. 701-703
Author(s):  
Federico Ferrini ◽  
Francesco Palla ◽  
Steven N. Shore
Keyword(s):  
Star Formation ◽  
Chemical Evolution ◽  
Galactic Halo ◽  
Stellar Populations ◽  
Galactic Evolution ◽  
Formation Model ◽  
Present Epoch ◽  
The Galaxy ◽  
Metal Abundance ◽  
History Of

The history of star formation in our galaxy is written in the metal abundance distributions of the stellar populations. Any star formation model is constrained by two facts. First, there was a period in the early stages of galactic evolution during which the metallicity of the gas out of which stars were being formed was significantly lower than the present epoch. Second, there is a paucity of extremely metal deficient stars in the disk of the galaxy.

scholarly journals The chemical evolution of iron-peak elements with hypernovae

2020 ◽  
Vol 496 (4) ◽  
pp. 4987-5001 ◽  
Author(s):  
J J Grimmett ◽  
Amanda I Karakas ◽  
Alexander Heger ◽  
Bernhard Müller ◽  
Christopher West
Keyword(s):  
Chemical Evolution ◽  
Significant Contribution ◽  
Extreme Values ◽  
Occurrence Rate ◽  
A Value ◽  
The Galaxy ◽  
Low Metallicity ◽  
Homogeneous Chemical ◽  
The Mean ◽  
Peak Abundance

ABSTRACT We calculate the mean evolution of the iron-peak abundance ratios [(Cr, Mn, Co, Zn)/Fe] in the Galaxy, using modern supernova and hypernova (HN) chemical yields and a Galactic Chemical Evolution code that assumes homogeneous chemical evolution. We investigate a range of HN occurrence rates and are able to produce a chemical composition that is a reasonable fit to the observed values in metal-poor stars. This requires an HN occurence rate that is large (50 per cent) in the early Universe, decreasing throughout evolution to a value that is within present-day observational constraints ($\lesssim 1{{\ \rm per\ cent}}$). A large HN occurrence rate is beneficial to matching the high [Zn/Fe] observed in the most metal-poor stars, although including HNe with progenitor mass $\ge 60\, \mathrm{M}_\odot$ is detrimental to matching the observed [(Mn, Co)/Fe] evolution at low [Fe/H]. A significant contribution from HNe seems to be critical for producing supersolar [(Co, Zn)/Fe] at low metallicity, though more work will need to be done in order to match the most extreme values. We also emphasize the need to update models for the enrichment sources at higher metallicity, as the satisfactory recovery of the solar values of [(Cr, Mn, Co, Zn)/Fe] still presents a challenge.

scholarly journals Neutron stars mergers in a stochastic chemical evolution model: impact of time delay distributions

2021 ◽  
Author(s):  
L Cavallo ◽  
G Cescutti ◽  
F Matteucci
Keyword(s):  
Time Delay ◽  
Neutron Star ◽  
Neutron Stars ◽  
Chemical Evolution ◽  
Galactic Halo ◽  
Massive Stars ◽  
Initial Mass Function ◽  
Evolution Model ◽  
Chemical Evolution Model ◽  
The Eu

Abstract We study the evolution of the [Eu/Fe] ratio in the Galactic halo by means of a stochastic chemical evolution model considering merging neutron stars as polluters of europium. We improved our previous stochastic chemical evolution model by adding a time delay distribution for the coalescence of the neutron stars, instead of constant delays. The stochastic chemical evolution model can reproduce the trend and the observed spread in the [Eu/Fe] data with neutron star mergers as unique producers if we assume: i) a delay time distribution ∝t−1.5, ii) a MEu = 3e − 6M⊙ per event, iii) progenitors of neutron stars in the range 9 − 50M⊙ and iv) a constant fraction of massive stars in the initial mass function (0.02) that produce neutron star mergers. Our best model is obtained by relaxing point iv) and assuming a fraction that varies with metallicity. We confirm that the mixed scenario with both merging neutron stars and supernovae as europium producers can provide a good agreement with the data relaxing the constraints on the distribution time delays for the coalescence of neutron stars. Adopting our best model, we also reproduce the dispersion of [Eu/Fe] at a given metallicity, which depends on the fraction of massive stars that produce neutron star mergers. Future high-resolution spectroscopic surveys, such as 4MOST and WEAVE, will produce the necessary statistics to constrain at best this parameter.

scholarly journals PSV-16 Infrared thermography technology as a promising tool for assessing temperament of water buffaloes

2020 ◽  
Vol 98 (Supplement_4) ◽  
pp. 220-221
Author(s):  
Caroline L Francisco ◽  
André M Castilhos ◽  
Daiane C Marques da Silva ◽  
Fabiola Martinez da Silva ◽  
Aline S Aranha ◽  
...  
Keyword(s):  
Infrared Thermography ◽  
Fixed Effects ◽  
Thermal Imager ◽  
Initial Body Weight ◽  
Water Buffaloes ◽  
Promising Tool ◽  
Genetic Groups ◽  
Body Regions ◽  
The Mean ◽  
Positive Correlations

Abstract This study evaluated the use of the infrared thermography (IT) as a tool to identify the temperament of 75 non-castrated water buffaloes (390±32 days of age; 310±61.27 kg of initial body weight) of 3 genetic groups (GG:Jafarabadi, Mediterranean, and Murrah; n = 25 for each GG). The animals were classified for temperament through the temperament score (TSc) obtained by the mean of the sum of the scores of the time of entry into the squeeze chute (1 to 5: 1=greater time spent for entry; 5=less time spent for entry) and the exit velocity score (1 to 5: 1=lower speed; 5=higher speed) calculated after the period of adaptation to the feedlot (d0). The animals were categorized into adequate (ADQ; TSc≤3) or excitable (EXC; TSc >3) temperaments. The rectal temperature was measured and IT images were obtained (Testo 882 Thermal Imager, Testo, Inc, Germany) from regions of the chest, eye, snout, cheek, foreleg (left side), ribs, hind legs, rear area (left side), and scrotum on d0. Data were analyzed using MIXED procedure in SAS, considering the GG, temperament, and the resulting interaction as fixed effects. Correlation was analyzed using the CORR procedure of SAS. There were no effects of interactions (P ≥ 0.14). ADQ animals showed lower rectal (P = 0.02) and ribs (P = 0.05) temperatures than EXC animals (Table1). Tendencies for temperament effect were detected for chest (P = 0.06) and rear area (P = 0.07). There was no effect of temperament for other variables (P = 0.19). Positive correlations were verified between the TSc and rectal (r=0.36; P < 0.01), chest (r=0.35; P < 0.01), and rear area (r=0.33; P < 0.01) temperatures. Tendency for a positive correlation was detected between TSc and scrotum (r=0.23; P = 0.07). In conclusion, the temperament causes changes in the temperature of some body regions suggesting the IT technology may be a promising tool for assessing the temperament of water buffaloes. Supported by FAPESP (#2018/25939-1; #2014/05473-7).

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