Abundance anomalies in main-sequence stars - Competition between diffusion processes and turbulent motions

1978 ◽  
Vol 223 ◽  
pp. 920 ◽  
Author(s):  
G. Vauclair ◽  
S. Vauclair ◽  
G. Michaud
Keyword(s):  
Main Sequence ◽  
Diffusion Processes ◽  
Main Sequence Stars ◽  
Abundance Anomalies

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.

scholarly journals Abundance anomalies in pre-main-sequence stars

2010 ◽  
Vol 526 ◽  
pp. A37 ◽  
Author(s):  
M. Vick ◽  
G. Michaud ◽  
J. Richer ◽  
O. Richard
Keyword(s):  
Main Sequence ◽  
Main Sequence Stars ◽  
Abundance Anomalies

scholarly journals Abundance Anomalies and Rotation in Main Sequence OB Stars

2004 ◽  
Vol 215 ◽  
pp. 209-217 ◽  
Author(s):  
A. Herrero ◽  
D. J. Lennon
Keyword(s):  
Angular Momentum ◽  
Main Sequence ◽  
Observational Evidence ◽  
Evolutionary Models ◽  
Surface Enrichment ◽  
Main Sequence Stars ◽  
Ob Stars ◽  
Chemical Surface ◽  
Abundance Anomalies ◽  
Class Iv

We review the present status of our knowledge about observational evidence of the influence of rotation on the evolution and chemical surface enrichment of OB Main Sequence stars. We pay special attention to the CNO elements and show that luminosity class IV-V OB stars provide a good reference point for abundance analyses.While there is clear evidence of rotationally induced mixing in OB stars, we show that fast rotation is not a guarantee of enrichment. A comparison of observed data with present evolutionary models indicates that the observed facts can be explained assuming that the stars are born with a distribution of rotational velocities, and that depending on the stellar mass the surface abundance changes will be dominated by rotation or mass loss. Only the existence of a large number of B supergiants beyond the Main Sequence cannot be explained in this scenario. We show that current evolutionary models including rotation do not adequately account for the transfer of angular momentum from the interior to the surface.We point out that the difficulty in determining He abundances and in knowing the present or past binary status of many stars leads us to consider the above conclusions as preliminary.

scholarly journals Progress in High S/N Spectroscopy and its Importance for Stellar Modelling

1993 ◽  
Vol 137 ◽  
pp. 108-121
Author(s):  
P.E. Nissen
Keyword(s):  
Large Deviations ◽  
Main Sequence ◽  
Diffusion Processes ◽  
Chemical Elements ◽  
The Sun ◽  
Main Sequence Stars ◽  
Solar Abundance ◽  
Recent Advances ◽  
Protostellar Cloud ◽  
Stellar Interiors

AbstractRecent advances in high S/N spectroscopy are reviewed with particular emphasis on new data for the abundances of chemical elements of importance for the modelling of stellar interiors.It seems well established that young, nearby B-type stars have abundances of CNO elements that are about a factor of two lower than in the Sun except for a small fraction of nitrogen-rich stars. The existence of such stars among main sequence stars remains to be explained.Among normal A-type stars (excluding Am and Ap stars) large deviations from solar abundance ratios occur with interesting anticorrelations of the abundances of C and Si. This suggests that diffusion processes and/or gas-dust separation of the chemical elements in the protostellar cloud play an important rôle.

scholarly journals Element Stratification in Main Sequence Stars and its Effect on Stellar Oscillations

2004 ◽  
Vol 193 ◽  
pp. 413-421
Author(s):  
Sylvie Vauclair
Keyword(s):  
Thermal Gradient ◽  
Main Sequence ◽  
Stellar Structure ◽  
Combined Effects ◽  
Main Sequence Stars ◽  
Stellar Oscillations ◽  
Peculiar Stars ◽  
Solar Type ◽  
Abundance Anomalies ◽  
Radiative Acceleration

AbstractElement settling due to the combined effects of gravity, thermal gradient, radiative acceleration and concentration gradient may lead to important abundance variations inside the stars that cannot be neglected in the computation of stellar structure. These processes were first introduced to account for abundance anomalies in “peculiar stars”, but their importance in the so-called “normal” stars is now fully acknowledged, specially after the evidence of helium settling in the Sun from helioseismology. These microscopic processes work in competition with macroscopic motions, such as rotation-induced mixing or mass loss, which increase the settling timescales. We have recently obtained clear evidence that asteroseismology of main sequence solar-type stars can give signatures of the chemical variations inside the stars and provide a better understanding of these processes.

scholarly journals Surface Abundance Anomalies of Main Sequence Stars in Globular Clusters — A Probe into Interactions between Stars

2003 ◽  
Vol 208 ◽  
pp. 445-446 ◽  
Author(s):  
Masaaki Shimada ◽  
Masayuki Y. Fujimoto ◽  
Shimako Yamada ◽  
Daiichiro Sugimoto
Keyword(s):  
Mass Transfer ◽  
Globular Clusters ◽  
Main Sequence ◽  
Red Giants ◽  
Main Sequence Stars ◽  
Giant Stars ◽  
Close Encounters ◽  
Dense Cores ◽  
Abundance Anomalies ◽  
Red Giant

In most of globular clusters, surface abundance anomalies are observed not only from red giant stars but also from main sequence stars. We discuss the possibility that the latter anomalies can be explained in terms the pollution due to mass transfer during close encounters with red giants, the latter of which have already developed the anomalies through their internal processes. If this is the case, the main sequence stars with the abundance anomalies may serve as a probe into the star-star interactions in dense cores of globular clusters.

scholarly journals Hα and OI Photometry of Upper Main Sequence Stars with Anomalous Abundances

1986 ◽  
Vol 90 ◽  
pp. 195-198 ◽  
Author(s):  
Eugenio E. ◽  
Mendoza V.
Keyword(s):  
Main Sequence ◽  
Main Sequence Stars ◽  
Abundance Anomalies ◽  
Ap Stars

AbstractAdditional α(16)Λ(9)-photometry of upper main sequence stars with anomalous abundances confirm our previous results, namely, Ap stars are neatly separated from normal main sequence stars. Furthermore, Ap stars are located on three different zones of the α(16)Λ(9)-plane, according to their abundance anomalies to form three photometric groups, (i) Si stars, (ii) Hg,Mn stars, and (iii) Cr,Eu,Sr stars.

Chromospheric activity as a function of age in main-sequence stars

1966 ◽  
Vol 24 ◽  
pp. 40-43
Author(s):  
O. C. Wilson ◽  
A. Skumanich
Keyword(s):  
Main Sequence ◽  
The Sun ◽  
Main Sequence Stars ◽  
Tentative Conclusion ◽  
Chromospheric Activity ◽  
General Field ◽  
Large Clusters

Evidence previously presented by one of the authors (1) suggests strongly that chromospheric activity decreases with age in main sequence stars. This tentative conclusion rests principally upon a comparison of the members of large clusters (Hyades, Praesepe, Pleiades) with non-cluster objects in the general field, including the Sun. It is at least conceivable, however, that cluster and non-cluster stars might differ in some fundamental fashion which could influence the degree of chromospheric activity, and that the observed differences in chromospheric activity would then be attributable to the circumstances of stellar origin rather than to age.

On The Radii of Ap Stars

1976 ◽  
Vol 32 ◽  
pp. 49-55 ◽  
Author(s):  
F.A. Catalano ◽  
G. Strazzulla
Keyword(s):  
Observational Data ◽  
Line Width ◽  
Main Sequence ◽  
Main Sequence Stars ◽  
Ap Stars

SummaryFrom the analysis of the observational data of about 100 Ap stars, the radii have been computed under the assumption that Ap are main sequence stars. Radii range from 1.4 to 4.9 solar units. These values are all compatible with the Deutsch's period versus line-width relation.

Pre–Main-Sequence Stars in the Young Galactic Cluster IC 4996: A CCD Photometric Study

1998 ◽  
Vol 116 (4) ◽  
pp. 1801-1809 ◽  
Author(s):  
Antonio J. Delgado ◽  
Emilio J. Alfaro ◽  
André Moitinho ◽  
José Franco
Keyword(s):  
Main Sequence ◽  
Photometric Study ◽  
Main Sequence Stars ◽  
Galactic Cluster
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