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.

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.

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

The Peculiar A Stars: Atmospheric Parameters and Abundance Peculiarities

1976 ◽  
Vol 32 ◽  
pp. 255-274 ◽  
Author(s):  
M. Hack
Keyword(s):  
Main Sequence ◽  
Atmospheric Parameters ◽  
Main Sequence Stars ◽  
Ap Stars ◽  
Large Groups

We have known for more than 40 years (Morgan 1933) that a group of stars having abnormal spectra exists among the main sequence stars included between B5 and F2. They represent at least 15% of the normal stars with the same color and luminosity.They can be divided in two large groups and their properties are summarized in Tables 1 and 2. They are the Ap stars (including the various subgroups, Mn stars, Si stars, Sr-Cr-Euor cool Ap stars) and the Am, Fm stars.

scholarly journals The Rotation of the Ap Stars From the Point of View of the Rigid Rotator Model

1970 ◽  
Vol 4 ◽  
pp. 254-263
Author(s):  
George W. Preston
Keyword(s):  
Distribution Function ◽  
Main Sequence ◽  
Point Of View ◽  
Main Sequence Stars ◽  
Rigid Rotator ◽  
Long Period ◽  
Rotator Model ◽  
Rotational Distribution ◽  
The Mean ◽  
Ap Stars

AbstractDeutsch’s period vs. line-width relation for the periodic Ap stars is re-examined from the point of view of the rigid rotator with the aid of recently determined values of v sin i for these objects. The agreement between computed rotational velocities and observed values of v sin i is satisfactory if the radii of the Ap stars are twice those of zero-age main sequence stars of the same color. The computed rotational velocities also agree with the mean rotational velocities of all Ap stars if suitable allowances are made for observational limitations. However, a difficulty arises in connection with the number of ‘long-period’ stars that have been discovered. Their small computed rotational velocities and their frequency are such that they cannot be regarded as part of any rotational distribution function that describes normal stars or even most Ap stars. It is concluded that if the periods of these objects are rotational periods, then a powerful rotational deceleration mechanism must be operative in at least some Ap stars, primarily those of the SrCrEu group.

scholarly journals Abundance and Magnetic Field Geometries of Helium-Strong and Helium-Weak Stars

1988 ◽  
Vol 132 ◽  
pp. 309-312
Author(s):  
David A. Bohlender ◽  
J. D. Landstreet
Keyword(s):  
Magnetic Field ◽  
High Temperature ◽  
Magnetic Fields ◽  
Main Sequence ◽  
Line Profiles ◽  
Main Sequence Stars ◽  
Hot Stars ◽  
Surface Magnetic Field ◽  
Peculiar Stars ◽  
Ap Stars

The helium-weak and helium-strong stars are main sequence stars with anomalously weak and strong helium lines for their spectral types respectively. Many members of the two classes have strong, globally ordered magnetic fields (Thompson and Landstreet 1985; Bohlender et al. 1987) and are currently thought to represent high temperature extensions of the Ap stars. In collaboration with C. T. Bolton (U. of Toronto), we have obtained high S/N phase resolved spectra of several stars using the coudé reticon detector at CFHT. One of the principle goals of this work is to determine abundance and surface magnetic field geometries of several helium peculiar stars with large, well-determined effective fields. We employ a line synthesis program (Landstreet 1987) that incorporates the effects of surface magnetic fields and non-uniform abundances on the observed line profiles of a star. Since these stars are rapid rotators the surface magnetic field strength must be inferred from differential magnetic intensification of lines with different magnetic sensitivities. Of the few lines with suitable strengths in these hot stars we have decided that the Si III multiplet 2 lines are best suited for this aspect of our investigation. We have also modelled the unblended He I line λ4437, ignoring magnetic effects for the time being. Individual results are discussed below.

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 Spectroscopy and Geography of Magnetic Ap Stars: Implications for Structure

1991 ◽  
Vol 145 ◽  
pp. 161-171
Author(s):  
J. D. Landstreet
Keyword(s):  
Large Scale ◽  
Main Sequence ◽  
Meridional Circulation ◽  
Field Structure ◽  
Surface Chemical ◽  
Main Sequence Stars ◽  
Chemical Abundances ◽  
B Stars ◽  
Uniform Distributions ◽  
Ap Stars

Some main sequence A and B stars have strong, ordered magnetic fields. These Ap and Bp stars usually have anomalous chemical abundances, and often rather non-uniform distributions of at least some elements (e.g. He, Ca, Ti, Cr) over their surfaces. Maps of magnetic field structure may provide a means of testing theories of how large coherent fields form, and of probing large-scale hydrodynamic flows (meridional circulation) inside stars. Maps of distributions of various elements can help to elucidate the mechanisms, such as diffusion under competing influences of gravity and radiation, turbulence, meridional circulation, mass loss, and perhaps accretion from the interstellar medium, that lead to the distinctive abundances and surface abundance distributions. This kind of mapping is important as an aid to understanding how the Ap and Bp stars develop. It is even more important because the processes involved in producing Ap and Bp stars probably have significant effects on surface chemical abundances of “normal” upper main sequence stars, and so understanding the relevant physics is essential to correctly relating observed surface chemistry to stellar and galactic evolution. In this paper, efforts to map field and abundance structures in Ap stars are reviewed, and some of the principal results obtained thus far are discussed.

scholarly journals The search for magnetic fields in mercury-manganese stars

2010 ◽  
Vol 6 (S272) ◽  
pp. 202-203
Author(s):  
Vitalii Makaganiuk ◽  
Oleg Kochukhov ◽  
Nikolai Piskunov ◽  
Sandra V. Jeffers ◽  
Christopher M. Johns-Krull ◽  
...  
Keyword(s):  
Magnetic Fields ◽  
Large Scale ◽  
Main Sequence ◽  
Chemical Elements ◽  
Field Measurements ◽  
Atomic Diffusion ◽  
Main Sequence Stars ◽  
Weak Magnetic Fields ◽  
Ap Stars ◽  
Spot Formation

AbstractMercury-manganese (HgMn) stars were considered to be non-magnetic, showing no evidence of surface spots. However, recent investigations revealed that some stars in this class possess an inhomogeneous distribution of chemical elements on their surfaces. According to our current understanding, the most probable mechanism of spot formation involves magnetic fields. Taking the advantage of a newly-built polarimeter attached to the HARPS spectrometer at the ESO 3.6m-telescope, we performed a high-precision spectropolarimetric survey of a large group of HgMn stars. The main purpose of this study was to find out how typical it is for HgMn stars to have weak magnetic fields. We report no magnetic field detection for any of the studied objects, with a typical precision of the longitudinal field measurements of 10 G and down to 1 Gauss for some of the stars. We conclude that HgMn stars lack large-scale magnetic fields typical of spotted magnetic Ap stars and probably lack any fields capable of creating and sustaining chemical spots. Our study confirms that alongside the magnetically altered atomic diffusion, there must be other structure formation mechanism operating in the atmospheres of late-B main sequence stars.

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