Helium surface distribution on He‐peculiar stars

Veto, B.; Hempelmann, A.; Schöneich, W.; Stahlberg, J.

doi:10.1002/asna.2113120216

Cited by 7 publications

(7 citation statements)

References 21 publications

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“…The line profile variations as well as the variations of the equivalent width and of the radial velocity of the He lines observed in our spectra support the models of a surface distribution with He-rich and He-weak hemispheres (Borra et al 1983;Vetö et al 1991). It is remarkable that the He I lines show some hint of splitting around the rotational phase 0.5.…”

Section: Observations and Spectrum Analysissupporting

confidence: 85%

Detection of variable Si II, Mn II, and Fe II emission lines in the magnetic Bp star a Centauri

Hubrig¹,

González²

2007

A&A

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Context. The nature of non-variable high-excitation emission lines detected in the optical spectra of normal late-B type and chemically peculiar HgMn and PGa stars is still poorly understood. Aims. To better understand the origin of the weak emission lines in B type stars it is especially important to investigate the spectra of a variety of stars to search for correlations between the emergence of these lines and fundamental stellar parameters. Methods. We have acquired high resolution UVES spectra for the sharp-lined magnetic helium-variable star a Cen over the rotation period of 8.82 d to search for the presence of weak emission lines. Results. For the first time we present observational evidence for the appearance of variable high-excitation Si II, Mn II and Fe II emission lines in a magnetic Bp star. Si II emissions are the strongest at the phase corresponding to the maximum strength of He I lines. Mn II and Fe II emissions vary in antiphase to the He I lines. A correlation is found between the probable location of Mn and Fe surface spots and the strength of the emission lines. On the basis of the currently available data it seems possible that the same kind of selective excitation process is working in the atmospheres of objects within a broad parameter space which could be defined by age, effective temperature, chemical composition, rotational velocity, and magnetic field. Neutral iron lines previously reported to appear broad and shallow at certain phases are not detected in our spectra, although two of them are identified as He I forbidden lines, showing maximum strength at the phase of the passage of the He rich region across the visible disk.

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Section: Observations and Spectrum Analysissupporting

confidence: 85%

Detection of variable Si II, Mn II, and Fe II emission lines in the magnetic Bp star a Centauri

Hubrig¹,

González²

2007

A&A

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“…It is well established that σ Ori E is a He‐strong star with patches of helium overabundance surrounded by regions of normal or deficient abundance (e.g. Veto et al 1991; Reiners et al 2000). Fig.…”

Section: Spectroscopymentioning

confidence: 99%

Revisiting the Rigidly Rotating Magnetosphere model for Ori E - I. Observations and data analysis★

Oksala¹,

Wade²,

Townsend³

et al. 2011

Monthly Notices of the Royal Astronomical Society

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We have obtained 18 new high‐resolution spectropolarimetric observations of the B2Vp star σ Ori E with both the Narval and ESPaDOnS spectropolarimeters. The aim of these observations is to test, with modern data, the assumptions of the Rigidly Rotating Magnetosphere (RRM) model of Townsend & Owocki, applied to the specific case of σ Ori E by Townsend, Owocki & Groote. This model includes a substantially offset dipole magnetic field configuration, and approximately reproduces previous observational variations in longitudinal field strength, photometric brightness and Hα emission. We analyse new spectroscopy, including H i, He i, C ii, Si iii and Fe iii lines, confirming the diversity of variability in photospheric lines, as well as the double S‐wave variation of circumstellar hydrogen. Using the multiline analysis method of least‐squares deconvolution (LSD), new, more precise longitudinal magnetic field measurements reveal a substantial variance between the shapes of the observed and RRM model time‐varying field. The phase‐resolved Stokes V profiles of He i 5876 and 6678 Å lines are fitted poorly by synthetic profiles computed from the magnetic topology assumed by Townsend et al.. These results challenge the offset dipole field configuration assumed in the application of the RRM model to σ Ori E, and indicate that future models of its magnetic field should also include complex, higher order components.

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“…He I λ 4026 photometry Pedersen & Thomsen (1977) and Pedersen (1979) published 53 measurements of a photometric index measuring the strength the He i λ4026 profile that we have transformed into an equivalent width measurement of the line by means of the relation derived by Vetö et al (1991).…”

Section: New Photometric Observationsmentioning

confidence: 99%

The extremely rapid rotational braking of the magnetic helium-strong star HD 37776

Mikulášek

Krtička²,

Henry

et al. 2008

A&A

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Context. Light and spectrum variations of the magnetic chemically peculiar (mCP) stars are explained by the oblique rigid rotator model with a rotation period usually assumed to be stable on a long time scale. A few exceptions, such as CU Vir or 56 Ari, have been reported as displaying an increase in their rotation period. A possible increase in the period of light and spectrum variations has also been suggested from observations of the helium-strong mCP star HD 37776 (V901 Ori). Aims. In this paper we attempt to confirm the possible period change of HD 37776 and discuss a possible origin of this change as a consequence of i) duplicity; ii) precession; iii) evolutionary changes; and iv) continuous/discrete/transient angular momentum loss. Results. We confirm the previously suspected gradual increase in the 1. d 5387 period of HD 37776 and find that it has lengthened by a remarkable 17.7 ± 0.7 s over the past 31 years. We also note that a decrease in the rate of the period change is not excluded by the data. The shapes of light curves in all colours were found to be invariable. Conclusions. After ruling out light-time effects in a binary star, precession of the rotational axis, and evolutionary changes as possible causes for the period change, we interpret this ongoing period increase as a braking of the star's rotation, at least in its surface layers, due to the momentum loss through events or processes in the extended stellar magnetosphere.

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Helium surface distribution on He‐peculiar stars

Cited by 7 publications

References 21 publications

Detection of variable Si II, Mn II, and Fe II emission lines in the magnetic Bp star a Centauri

Detection of variable Si II, Mn II, and Fe II emission lines in the magnetic Bp star a Centauri

Revisiting the Rigidly Rotating Magnetosphere model for Ori E - I. Observations and data analysis★

The extremely rapid rotational braking of the magnetic helium-strong star HD 37776

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