scholarly journals A Flatter metallicity gradient in the Galactic disk: non-LTE abundance calculations of OB stars

2003 ◽  
Vol 212 ◽  
pp. 162-163 ◽  
Author(s):  
Simone Daflon ◽  
Katia Cunha
Keyword(s):  
Main Sequence ◽  
Galactic Disk ◽  
Main Sequence Stars ◽  
Chemical Abundances ◽  
Stellar Abundances ◽  
Ob Stars ◽  
The Galaxy ◽  
Aluminum Silicon

We present non-LTE abundances of carbon, nitrogen, oxygen, magnesium, aluminum, silicon and sulfur, derived for a sample of 70 O9-B2 main sequence stars of the Galactic disk and analyze the distribution of the chemical abundances in terms of radial gradients within 4.4-12.9 kpc from the center of the Galaxy. The derived gradients are flatter than those presented by the most recent studies about the radial gradients of stellar abundances.

scholarly journals Chemical Abundances in Planetary Nebulae

1978 ◽  
Vol 76 ◽  
pp. 215-224 ◽  
Author(s):  
Manuel Peimbert
Keyword(s):  
Main Sequence ◽  
Galactic Disk ◽  
Type Ii ◽  
Orion Nebula ◽  
Main Sequence Stars ◽  
Chemical Abundances ◽  
Element Abundances ◽  
Oxygen Gradient ◽  
The Galaxy ◽  
Halo Population

PN can be divided into four types depending on their chemical composition. In order of decreasing heavy element abundances the types are: I) He and N rich, II) intermediate population, III) high velocity, and IV) halo population. The type II PN are overabundant in N and C relative to the Orion Nebula. Well defined gradients across the galactic disk of He, N and O are derived from type II PN; the oxygen gradient is similar to the metallicity gradient derived from GK giants and F main sequence stars. By comparing the O, Ne and S abundances of PN of types III and IV with the Fe abundances of stars of similar population it is found that the O, Ne and S enrichment in the Galaxy probably took place before the Fe enrichment.

scholarly journals Are sdAs helium core stars?

2017 ◽  
Vol 26 (1) ◽  
Author(s):  
Ingrid Pelisoli ◽  
S. O. Kepler ◽  
Detlev Koester
Keyword(s):  
Main Sequence ◽  
Galactic Disk ◽  
Physical Nature ◽  
Sloan Digital Sky Survey ◽  
Distance Modulus ◽  
Main Sequence Stars ◽  
Sky Survey ◽  
Balmer Lines ◽  
Low Mass ◽  
Binary Evolution

AbstractEvolved stars with a helium core can be formed by non-conservative mass exchange interaction with a companion or by strong mass loss. Their masses are smaller than 0.5 M⊙. In the database of the Sloan Digital Sky Survey (SDSS), there are several thousand stars which were classified by the pipeline as dwarf O, B and A stars. Considering the lifetimes of these classes on the main sequence, and their distance modulus at the SDSS bright saturation, if these were common main sequence stars, there would be a considerable population of young stars very far from the galactic disk. Their spectra are dominated by Balmer lines which suggest effective temperatures around 8 000-10 000 K. Several thousand have significant proper motions, indicative of distances smaller than 1 kpc. Many show surface gravity in intermediate values between main sequence and white dwarf, 4.75 < log g < 6.5, hence they have been called sdA stars. Their physical nature and evolutionary history remains a puzzle. We propose they are not H-core main sequence stars, but helium core stars and the outcomes of binary evolution. We report the discovery of two new extremely-low mass white dwarfs among the sdAs to support this statement.

scholarly journals Pulsations of Ob-Stars: New Observations

1998 ◽  
Vol 185 ◽  
pp. 347-354 ◽  
Author(s):  
Dietrich Baade
Keyword(s):  
Main Sequence ◽  
Physical Parameters ◽  
Be Stars ◽  
Instability Strip ◽  
Ob Stars ◽  
Analysis Strategies ◽  
The Galaxy ◽  
Order Line ◽  
Nonradial Pulsation ◽  
Radial Pulsations

Improved observing and data analysis strategies have initiated a considerable expansion of the empirical knowledge about the pulsations of OB stars. Possible correlations between physical parameters and associated pulsation characteristics are becoming more clearly perceivable. This starts to include the asteroseismologically fundamental areas of g-modes and rapid rotation. The β Cephei instability strip continues to be the only locus where radial pulsations occur (but apparently not in all stars located in that strip). Except for spectral types B8/B9 near the main sequence, where pulsations are hardly detected even at low amplitudes, any major group of stars in the Galaxy that are obviously not candidate pulsators still remains to be identified. However, the incidence and amplitudes of OB star pulsations decrease steeply with metallicity. The behaviour of high-luminosity stars is less often dominated by very few modes. In broad-lined stars the moving-bump phenomenon is more common than low-order line-profile variability. But its relation to nonradial pulsation is not clear. The beating of low-ℓ nonradial pulsation modes that have identical angular mode indices may be the clockwork of the outbursts of at least some Be stars. The physics of this episodic mass loss process remains to be identified.

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 A high-spectral-resolution study of abundances and isotopic composition of BHB stars in NGC 6397 and NGC 6752

2009 ◽  
Vol 5 (S266) ◽  
pp. 421-421
Author(s):  
S. Hubrig ◽  
F. Castelli ◽  
G. De Silva ◽  
J. F. González ◽  
Y. Momany ◽  
...  
Keyword(s):  
Globular Clusters ◽  
Main Sequence ◽  
High Spectral Resolution ◽  
Horizontal Branch ◽  
Main Sequence Stars ◽  
Chemical Abundances ◽  
Chemically Peculiar ◽  
Abundance Anomalies ◽  
Isotopic Anomalies ◽  
Resolution Study

AbstractLarge abundance anomalies have previously been detected in horizontal-branch B-type stars. We present the first high-resolution study of isotopic anomalies and chemical abundances in six horizontal-branch B-type stars in the globular clusters NGC 6397 and NGC 6752, carried out with UVES on the VLT and compare them to those observed in chemically peculiar main-sequence stars.

The Nature of the Triangulum-Andromeda Stellar Structures

2018 ◽  
Vol 14 (S344) ◽  
pp. 122-124
Author(s):  
J. V. Sales Silva ◽  
H. Perottoni ◽  
K. Cunha ◽  
H. J. Rocha-Pinto ◽  
D. Souto ◽  
...  
Keyword(s):  
High Resolution ◽  
Kinematic Analysis ◽  
Dwarf Galaxies ◽  
Galactic Disk ◽  
Thin Disk ◽  
Atmospheric Parameters ◽  
Chemical Abundances ◽  
The Galaxy ◽  
Stellar Halo ◽  
Debris Cloud

AbstractThe outer stellar halo is home to a number of substructures that are remnants of former interactions of the Galaxy with its dwarf satellites. Triangulum-Andromeda (TriAnd) is one of these halo substructures, found as a debris cloud by Rocha-Pinto et al., (2004) using 2MASS M giants. Would be these structures related to dwarf galaxies or to the galactic disk? To uncover the nature of these stars we performed a high-resolution spectroscopic study (R = 40,000) along with a kinematic analysis using Gaia data. We determined the atmospheric parameters and chemical abundances of Ca and Mg for the 13 TriAnd candidate stars along with their respective orbits. Our results indicate that the TriAnd stars analyzed have a galactic nature but that these stars are not from the local thin disk.

scholarly journals Some Regularities in Chemical Composition of Unevolved Main Sequence Stars and Synthesis of the Elements

1977 ◽  
Vol 45 ◽  
pp. 177-179
Author(s):  
V.L. Khokhlova
Keyword(s):  
Chemical Composition ◽  
Main Sequence ◽  
Published Data ◽  
Main Sequence Stars ◽  
Chemical Abundances

The published data on chemical abundances derived from fine analysis for about 80 G, F and A main sequence stars are analysed. The following conclusions are drawn :

scholarly journals Chemical Abundances in Main Sequence Stars

2002 ◽  
Vol 12 ◽  
pp. 262-264 ◽  
Author(s):  
John D. Landstreet
Keyword(s):  
Main Sequence ◽  
Main Sequence Stars ◽  
Chemical Abundances

AbstractThis talk reviews recent results relevant to identifying and constraining the processes that mix and transport specific elements in the envelopes of main sequence stars.

scholarly journals Stellar statistics along the ecliptic and the impact on the K2 mission concept

2014 ◽  
Vol 14 (2) ◽  
pp. 165-172 ◽  
Author(s):  
Andrej Prša ◽  
Annie Robin ◽  
Thomas Barclay
Keyword(s):  
Main Sequence ◽  
Target Selection ◽  
Ecliptic Plane ◽  
Galactic Latitude ◽  
Gold Mine ◽  
Main Sequence Stars ◽  
Satellite Attitude ◽  
The Galaxy ◽  
Orbital Periods ◽  
The Impact

AbstractK2 is the mission concept for a repurposedKeplermission that uses two reaction wheels to maintain the satellite attitude and provide ~81 days of coverage for ten 105 deg2fields along the ecliptic in the first 2.5 years of operation. We examine stellar populations based on the updated Besançon model of the Galaxy, comment on the general properties for the entire ecliptic plane, and provide stellar occurrence rates in the first six tentative K2 campaigns grouped by spectral type and luminosity class. For each campaign we distinguish between main the sequence stars and giants, and provide their density profile as a function of galactic latitude. We introduce the crowding metric that serves for optimized target selection across the campaigns. For all main sequence stars we compute the expected planetary occurrence rates for three planet sizes: 2–4, 4–8 and 8–32 R⊕with orbital periods up to 50 days. In conjunction with Gaia and the upcoming Transiting Exoplanet Survey Satellite and Plato missions, K2 will become a gold mine for stellar and planetary astrophysics.

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