Atmospheric Variations in Chemically Peculiar Stars

Kroll, R.

doi:10.1007/978-3-642-75183-7_18

Cited by 7 publications

(19 citation statements)

References 8 publications

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“…This allows us to conclude that the chemical spots do not lead to the observed Balmer line variations. This fact is in concordance with the results obtained by Kroll (1989), who showed that the found shape of the Balmer line variability cannot be reproduced by metallicity or temperature variations, but can be considered in the frame of changes in the pressure structure of the stellar atmosphere. Finally, the average abundances from Table 2 (last column) were used in the rest of model atmosphere calculations.…”

Section: Effects Of Horizontal Abundance Distributionsupporting

confidence: 92%

“…We have detected and studied variability of the Starkbroadened profiles of Hα, Hβ, and Hγ. Several proofs of the presence of significant Lorentz force in the atmosphere of θ Aur have been found: -The characteristic shape of the variation during a full rotation cycle of the star corresponds to those described by Kroll (1989) and other authors (Valyavin et al 2004, and references therein) as a result of the impact of a substantial Lorentz force. -Numerical calculations of the model atmospheres with individual abundances demonstrate that the surface chemical spots cannot produce the observed variability in the hydrogen line profiles of θ Aur.…”

Section: Discussionmentioning

confidence: 55%

“…The standard deviations at the Hβ and Hγ reveal the characteristic fingerprint first described by Kroll (1989) as the impact of the Lorentz force: the amplitude rises in the wings and drops to the line center. This picture is less clear for the Hα line due to the above reasons and strong distortion of the profile by the telluric molecular absorptions.…”

Section: Observationsmentioning

confidence: 62%

“…Spectroscopy of the hydrogen lines also points in this direction. Kroll (1989) found variability with amplitudes more than 1% in the Balmer lines in several magnetic stars. He showed that at least part of this variability can be attributed to the presence of a non-zero Lorentz force in stellar atmospheres.…”

Section: Introductionmentioning

confidence: 91%

“…However, the situation has been significantly improved with the development of highly stable fiber-fed spectrographs that made it possible to carry out these studies at a more advanced instrumental level. Taking this into account and following the pioneering work by Kroll (1989), we have initiated a new spectroscopical search for hydrogen-line variability (Valyavin et al 2005).…”

Section: Introductionmentioning

confidence: 99%

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The Lorentz force in atmospheres of CP stars:θ Aurigae

Shulyak¹,

Valyavin

Kochukhov

et al. 2007

A&A

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Several dynamical processes may induce considerable electric currents in the atmospheres of magnetic chemically peculiar (CP) stars. The Lorentz force, which results from the interaction between the magnetic field and the induced currents, modifies the atmospheric structure and induces the characteristic rotational variability in the hydrogen Balmer lines. To study this phenomena we have initiated a systematic spectroscopic survey of the Balmer lines variation in magnetic CP stars. In this paper we continue presenting the results of the program, focusing on the high-resolution spectral observations of the A0p star θ Aur (HD 40312). We detected a significant variability in the Hα, Hβ, and Hγ spectral lines during the full rotation cycle of the star. This variability is interpreted in the framework of the model atmosphere analysis, which accounts for the Lorentz force effects. Both the inward-and outward-directed Lorentz forces are considered under the assumption of the axisymmetric dipole or dipole+quadrupole magnetic field configurations. We demonstrate that only the model with the outwardly directed Lorentz force in the dipole+quadrupole configuration is able to reproduce the observed hydrogen-line variation. These results present new strong evidence of non-zero global electric currents in the atmosphere of an earlytype magnetic star.

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Section: Effects Of Horizontal Abundance Distributionsupporting

confidence: 92%

Section: Discussionmentioning

confidence: 55%

Section: Observationsmentioning

confidence: 62%

Section: Introductionmentioning

confidence: 91%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

The Lorentz force in atmospheres of CP stars:θ Aurigae

Shulyak¹,

Valyavin

Kochukhov

et al. 2007

A&A

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Atmospheric models of He-peculiar stars: synthetic He I line profiles and absolute visual magnitudes

Vallverdú

Cidale

Rohrmann

et al. 2014

Astrophys Space Sci

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We analyze the influence of magnetic pressure effects on the atmospheric structure of B peculiar type stars, as well as, on the emergent He I line profiles and absolute visual magnitudes.We consider a photosphere in local thermodynamic and hydrostatic equilibrium. The hydrostatic equilibrium equation is modified to include the Lorentz force. Atomic occupational numbers are computed in LTE considering nonideal effects in the gas equation of state.We depict the influence of a magnetic field on local He I line profiles and discuss the effects of the helium abundance in magnetic B-type stars. The Lorentz force might explain local variations up to 7 % in the equivalent width of helium lines, while local enhancements of He chemical abundances would produce larger changes. To analyze the line variations in real stars we computed the net contribution of a bipolar magnetic field over the stellar disk. The resulting diskaveraged magnetic field predicts variations with the rotation phase up to 2-3 % in the line EWs for a dipolar magnetic field of 1000 G.

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Analysis of magnetic pressure effects in atmospheres of CP stars

et al. 2008

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Abstract. Several dynamical processes may induce considerable Lorentz forces in atmospheres of mCP stars, thus modifying the hydrostatic structure of their atmospheres. This modification can be seen as characteristic rotational variability of certain spectral features such as hydrogen Balmer lines. In this work we present the first results of modeling the magnetic pressure effects in atmospheres of mCP stars in the framework of model atmosphere analysis with accurate treatment of microscopic properties of atmospheric plasma. We show that at least part of the rotational variability of hydrogen lines seen in high-resolution spectra of mCP stars could be attributed to the non-zero electrical currents flowing along stellar surfaces.

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Atmospheric Variations in Chemically Peculiar Stars

Cited by 7 publications

References 8 publications

The Lorentz force in atmospheres of CP stars:θ Aurigae

The Lorentz force in atmospheres of CP stars:θ Aurigae

Atmospheric models of He-peculiar stars: synthetic He I line profiles and absolute visual magnitudes

Analysis of magnetic pressure effects in atmospheres of CP stars

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