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.

Long-period modulated superstructures in Pd-12.5 at.%Ce and Pd-15 at.%Ce alloys

1990 ◽  
Vol 48 (4) ◽  
pp. 164-165
Author(s):  
Noriyuki Kuwano ◽  
Masaru Itakura ◽  
Kensuke Oki
Keyword(s):  
Electron Microscopy ◽  
Mean Value ◽  
Heavy Elements ◽  
Arc Furnace ◽  
X Ray ◽  
Long Period ◽  
Ultra High Purity ◽  
Heat Treated ◽  
Atomic Scattering ◽  
The Mean

Pd-Ce alloys exhibit various anomalies in physical properties due to mixed valences of Ce, and the anomalies are thought to be strongly related with the crystal structures. Since Pd and Ce are both heavy elements, relative magnitudes of (fcc-fpd) are so small compared with <f> that superlattice reflections, even if any, sometimes cannot be detected in conventional x-ray powder patterns, where fee and fpd are atomic scattering factors of Ce and Pd, and <f> the mean value in the crystal. However, superlattices in Pd-Ce alloys can be analyzed by electron microscopy, thanks to the high detectability of electron diffraction. In this work, we investigated modulated superstructures in alloys with 12.5 and 15.0 at.%Ce.Ingots of Pd-Ce alloys were prepared in an arc furnace under atmosphere of ultra high purity argon. The disc specimens cut out from the ingots were heat-treated in vacuum and electrothinned to electron transparency by a jet method.

scholarly journals Isotopic and Elemental Determination in Some Romanian Apple Fruit Juices

2012 ◽  
Vol 2012 ◽  
pp. 1-7 ◽  
Author(s):  
Dana Alina Magdas ◽  
Adriana Dehelean ◽  
Romulus Puscas
Keyword(s):  
Drinking Water ◽  
Apple Fruit ◽  
Mean Value ◽  
Heavy Elements ◽  
Stable Isotope Ratios ◽  
Mean Values ◽  
Ni Content ◽  
Elemental Determination ◽  
Us Epa ◽  
The Mean

H, C, O stable isotope ratios and the content of some heavy elements of 31 Romanian single-strength organic apple juices collected from four Transylvanian areas are discussed in this study. The aim of this study was to measure the2H/1H,18O/16O,13C/12C ratios of these juices and their elemental profile and to establish a database of authentic values to be used for adulteration and authenticity testing. Our results have shown mean values ofδ18O=-4.2‰andδDδ-46.5‰, respectively, for apples from Transylvania and at the same time the mean value ofδ13C=-28.2‰. The content of Cd, Pb, U, Zn, As was below the acceptable limits stipulated in US-EPA standard for drinking water. Cu and Cr limits exceeded for one single juice; Ni content for some apple juices from Maramures, Alba, and Cluj was higher than the acceptable value.

scholarly journals The Evolution of 3He, 4He and D in the Galaxy

2000 ◽  
Vol 198 ◽  
pp. 540-546 ◽  
Author(s):  
Cristina Chiappini ◽  
Francesca Matteucci
Keyword(s):  
Chemical Evolution ◽  
Present Model ◽  
Galactic Disk ◽  
The Sun ◽  
Mixing Process ◽  
Low Mass Stars ◽  
A Value ◽  
The Galaxy ◽  
Low Mass ◽  
Standing Problem

In this work we present the predictions of a modified version of the ‘two-infall model’ (Chiappini et al. 1997 - CMG) for the evolution of 3He, 4He and D in the solar vicinity, as well as their distributions along the Galactic disk. In particular, we show that when allowing for extra-mixing process in low mass stars (M < 2.5 M⊙), as predicted by Charbonnel and do Nascimento (1998), a long standing problem in chemical evolution is solved, namely: the overproduction of 3He by the chemical evolution models as compared to the observed values in the sun and in the interstellar medium. Moreover, we show that chemical evolution models can constrain the primordial value of the deuterium abundance and that a value of (D/H)p < 3 × 10—5 is suggested by the present model. Finally, adopting the primordial 4He abundance suggested by Viegas et al. (1999), we obtain a value for ΔY/ΔZ ≃ 2 and a better agreement with the solar 4He abundance.

scholarly journals Chemical Abundances in Galactic Bulge Pn

1993 ◽  
Vol 155 ◽  
pp. 581-581 ◽  
Author(s):  
N.A. Walton ◽  
M.J. Barlow ◽  
R.E.S. Clegg
Keyword(s):  
Galactic Disk ◽  
Planetary Nebulae ◽  
Solar Neighbourhood ◽  
Galactic Bulge ◽  
Low Resolution ◽  
Chemical Abundances ◽  
The Mean ◽  
Optical Spectrophotometry ◽  
High Metallicity

We present abundance determinations, in particular of carbon, and C/O ratios, for 11 Galactic bulge planetary nebulae (PN) based on our low resolution UV data from IUE observations and optical spectrophotometry from the Anglo-Australian Telescope. We compare the observed abundances with those predicted by dredge-up theory for the high metallicity Galactic bulge. The sample abundances are also contrasted with the abundances found for PN in the Galactic disk. The mean C/O ratio for the bulge PN is significantly lower than that found for Galactic disk PN. Further, we present an abundance analysis of the very metal-poor bulge PN M2-29. From an analysis of the differential extinction found from the observed ratios of the He ii 1640,4686Å lines, we find that the ultraviolet reddening law towards the bulge is steeper than in the solar neighbourhood.

scholarly journals Interstellar and Stellar Abundances Across the Galactic Disk

1977 ◽  
Vol 45 ◽  
pp. 149-159 ◽  
Author(s):  
Manuel Peimbert
Keyword(s):  
Chemical Composition ◽  
Density Distribution ◽  
Chemical Evolution ◽  
Galactic Disk ◽  
Theoretical Models ◽  
Observational Evidence ◽  
Stellar Abundances ◽  
Abundance Gradient ◽  
The Galaxy

Abstract.Observational evidence related to the chemical composition across the disk of the Galaxy is reviewed. The H2density distribution derived for the Galaxy is poorly known, consequently it is still not possible to compare theoretical models of the chemical evolution of the Galaxy with the gaseous density distribution. The H2density distribution is particularly sensitive to the fraction of carbon atoms embedded in CO molecules and to the possible presence of a C/H abundance gradient.

scholarly journals Determination of the C/M5+ Ratio in the Galactic Disk

1995 ◽  
Vol 148 ◽  
pp. 276-279
Author(s):  
Francisco J. Fuenmayor
Keyword(s):  
Near Infrared ◽  
Galactic Center ◽  
Galactic Disk ◽  
Mean Value ◽  
Galactocentric Distance ◽  
The Galaxy ◽  
Metal Abundance ◽  
Objective Prism ◽  
M Stars

AbstractA determination of the C/M5+ ratio, as a function of the galactocentric distance, in the galactic disk is presented. These results are based upon previous determinations of the space density for cool carbon stars and for late giant M stars in the Milky Way. Most of these results were obtained from objective-prism surveys in the near infrared using mainly Schmidt-type telescopes. The ratio C/M5+ appears to increase from 0.05 to 0.25 in the galactic disk, from the galactic center outwards. A mean value of 0.15 of this ratio for the Galaxy is suggested. Correlations between the C/M5+ ratio and currently known metal abundance gradients in the galactic disk are discussed.

scholarly journals The UV and optical reddening law to the Galactic Bulge and CNO abundances in Bulge planetary nebulae

1993 ◽  
Vol 153 ◽  
pp. 337-338
Author(s):  
N.A. Walton ◽  
M.J. Barlow ◽  
R.E.S. Clegg
Keyword(s):  
Galactic Disk ◽  
Planetary Nebulae ◽  
Line Ratio ◽  
Solar Neighbourhood ◽  
Balmer Line ◽  
Galactic Bulge ◽  
The Mean ◽  
Cno Abundances ◽  
Halo Population ◽  
Selective Extinction

An analysis of the differential ultraviolet extinction towards four bulge planetary nebulae, based on the observed line ratio of He II 1640/4686Å, shows that the ultraviolet reddening law towards the bulge is much steeper than in the solar neighbourhood. An analysis of the optical reddening law for 42 bulge PN, based upon observed Balmer line ratios and Hβ to radio free-free flux ratios, is presented. The optical reddening law towards the bulge is steeper than in the local ISM, and thus the ratio of total to selective extinction, Rv = 2.29 (± 0.50), is lower than the standard solar neighbourhood value of Rv = 3.10.We present abundance determinations, in particular C/H and C/O ratios, for 11 Galactic bulge PN, based on spectrophotometry in the UV from IUE and in the optical from the Anglo-Australian Telescope. The derived abundances are compared with values for PN in the Galactic disk. The mean C/O ratio for bulge PN is significantly lower than that found for Galactic disk PNs. Additionally we present an abundance analysis of the very metal-poor halo population PN M2-29, which is located in the bulge.

scholarly journals Microstructure of the Galactic Magnetic Field

1958 ◽  
Vol 8 ◽  
pp. 952-954
Author(s):  
K. Serkowski
Keyword(s):  
Magnetic Field ◽  
Position Angle ◽  
Mean Value ◽  
Open Clusters ◽  
Electric Vector ◽  
Stokes Parameters ◽  
Galactic Magnetic Field ◽  
The Mean ◽  
Image Position

The polarization of the stars in open clusters, explained on the basis of the Davis-Greenstein theory, gives some information on the microstructure of the galactic magnetic field.The polarization is most conveniently described by the parameters Q, U, proportional to the Stokes parameters and defined by where p is the amount of polarization, θ is the position angle of the electric vector, and θ̄ is the mean value of θ for the region under consideration.

scholarly journals Helium abundances in planetary nebulae: Nucleosynthesis and chemical evolution

2009 ◽  
Vol 5 (S268) ◽  
pp. 181-182
Author(s):  
W. J. Maciel ◽  
R. D. D. Costa ◽  
T. E. P. Idiart
Keyword(s):  
Chemical Evolution ◽  
Planetary Nebulae ◽  
Magellanic Clouds ◽  
Heavy Elements ◽  
Solar Neighbourhood ◽  
Host Galaxies ◽  
Intermediate Mass ◽  
Large Sample ◽  
Intermediate Mass Stars ◽  
Progenitor Stars

AbstractWe have obtained a large sample of PN with accurately determined helium abundances, as well as abundances of several heavy elements. The nebulae are located in the solar neighbourhood, in the galactic bulge, disk and anticentre, and in the Magellanic Clouds. The abundances are analyzed both in terms of the nucleosynthesis of intermediate mass stars and the chemical evolution of the host galaxies. In particular, correlations between the He/H ratio and the abundances of N and O are used as constraints of the nucleosynthetic processes occurring in the progenitor stars.

scholarly journals The Geneva–Copenhagen Survey of the Solar Neighbourhood

2004 ◽  
Vol 21 (2) ◽  
pp. 129-133 ◽  
Author(s):  
B. Nordström ◽  
J. Andersen ◽  
J. Holmberg ◽  
B. R. Jørgensen ◽  
M. Mayor ◽  
...  
Keyword(s):  
Binary Stars ◽  
Galactic Disk ◽  
Classical Model ◽  
Thin Disk ◽  
Solar Neighbourhood ◽  
Proper Motions ◽  
Kinematic Data ◽  
Model Predictions ◽  
The Mean ◽  
Metallicity Distribution

AbstractWe report on a new survey of metallicities, ages, and Galactic orbits for a complete, magnitude-limited, and kinematically unbiased all-sky sample of 16 682 nearby F- and G-dwarfs. Our ∼ 63 000 new, accurate radial velocities for nearly 13 500 of the stars, combined with Hipparcos parallaxes and Tycho-2 proper motions, complete the kinematic data for 14 139 stars and allow us to identify most of the binary stars in the sample. Isochrone ages have been determined whenever reliable results are possible, with particular attention to realistic error estimates.Among the basic properties of the Galactic disk that can be reinvestigated from our data are the metallicity distribution of G-dwarfs and the age–metallicity and age–velocity relations of the solar neighbourhood. We confirm the lack of metal-poor G-dwarfs relative to classical model predictions (the 'G-dwarf problem'), the near-constancy of the mean metallicity since the formation of the thin disk, and the appearance of the kinematic signature of the thick disk ∼ 10 Gyr ago.

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