The light variability of the helium strong star HD 37776 as a result of its inhomogeneous elemental surface distribution

Krtička, Jiřı́; Mikulášek, Zdeněk; Zverko, J.; Ziznovsky, J.

doi:10.1051/0004-6361:20066627

Cited by 75 publications

(102 citation statements)

References 42 publications

(71 reference statements)

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“…Molnar concluded that neither the photometric variability nor the ultraviolet Si line variations were due to a variation in T eff over the rotation cycle of the star. Krticka et al (2007) have also demonstrated that the light curve of the heliumstrong star HD 37776, an object quite comparable to a Cen in fundamental properties and in having quite pronounced line profile variations, can be almost completely accounted for by the inhomogeneous surface distribution of silicon and helium over the star's surface and the bound-free transitions of these elements and not surface temperature variations. More recent work on a cooler Ap star, HR 7224, also suggests that surface temperature variations do not exist in Ap stars (Krticka et al 2009).…”

Section: Doppler Imagingmentioning

confidence: 90%

Doppler imaging of the helium-variable star a Centauri

Bohlender¹,

Rice²,

Hechler³

2010

A&A

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Aims. The helium-peculiar star a Cen exhibits interesting line profile variations of elements such as iron, nitrogen and oxygen in addition to its well-known extreme helium variability. The objective of this paper is to use new high signal-to-noise, high-resolution spectra to perform a quantitative measurement of the helium, iron, nitrogen and oxygen abundances of the star and determine the relation of the concentrations of the heavier elements on the surface of the star to the helium concentration and perhaps to the magnetic field orientation. Methods. Doppler images have been created for the elements helium, iron, nitrogen and oxygen using the programs described in earlier papers by Rice and others. An alternative surface abundance mapping code has been used to model the helium line variations after our Doppler imaging of certain individual helium lines produced mediocre results. Results. Doppler imaging of the helium abundance of a Cen confirms the long-known existence of helium-rich and helium-poor hemispheres on the star and we measure a difference of more than two orders of magnitude in helium abundance from one side of the star to the other. Helium is overabundant by a factor of about 5 over much of the helium-rich hemisphere. Of particular note is our discovery that the helium-poor hemisphere has a very high abundance of 3 He, approximately equal to the 4 He abundance. a Cen is therefore a new member of the small group of helium-3 stars and the first well-established magnetic member of the class. For the three metals investigated here, there are two strong concentrations of abundance near the equator at longitude roughly 135 • consistent with the positive magnetic maximum and two somewhat weaker concentrations of abundance near longitude 315 • on the equator near where the helium concentration is centered and roughly where the negative peak of the magnetic field would be found. Another strong concentration is found near the equator at about longitude 45 • and this is not explainable in terms of any simple symmetry with the helium abundance or the apparent magnetic field main polar locations.

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Section: Doppler Imagingmentioning

confidence: 90%

Doppler imaging of the helium-variable star a Centauri

Bohlender¹,

Rice²,

Hechler³

2010

A&A

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“…The photospheric line profiles of these elements hence vary with the rotation period of the star, and the variations in the lines from different elements are typically not identical (e.g., Briquet et al 2001Briquet et al , 2004Lehmann et al 2006). In addition, stars with a patchy surface abundance pattern are known to show rotationally modulated light variability (Krtička et al 2007(Krtička et al , 2009. From the Hipparcos light-curve of HD 202850, Koen & Eyer (2002) derived a putative (but not yet confirmed) period of 120.2 d. This period might be caused by stellar rotation, but the value of sin i = 33 ± 2 km s −1 obtained by Markova & Puls (2008) limits the rotation period to P ≤ (83 ± 5) d.…”

Section: Discussionmentioning

confidence: 97%

Detection of a 1.59 h period in the B supergiant star HD 202850

Kraus¹,

Tomić²,

Oksala³

et al. 2012

A&A

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Context. Photospheric lines of B-type supergiants show variability in their profile shapes. In addition, their widths are much wider than can be accounted for purely by stellar rotation. This excess broadening is often referred to as macroturbulence. Both effects have been linked to stellar oscillations, but B supergiants have not been systematically searched yet for the presence of especially short-term variability caused by stellar pulsations. Aims. We have started an observational campaign to investigate the line profile variability of photospheric lines in a sample of Galactic B supergiants. These observations aim to improve our understanding of the physical effects acting in the atmospheres of evolved massive stars. Methods. We obtained four time-series of high-quality optical spectra for the Galactic B supergiant HD 202850. The spectral coverage of about 500 Å around Hα encompasses the Si ii λλ6347, 6371, and the He i λ6678 photospheric lines. The line profiles were analysed by means of the moment method. Results. The time-series of the photospheric Si ii and He i lines display a simultaneous, periodic variability in their profile shapes. Proper analysis revealed a period of 1.59 h in all three lines. This period is found to be stable with time over the observed span of 19 months. This period is much shorter than the rotation period of the star and might be ascribed to stellar oscillations. Since the star seems to fall outside the currently known pulsational instability domains, the nature of the discovered oscillation remains unclear.

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“…It is also one of the few spotted stars for which the rotational spin-down has been directly measured (Mikulášek et al 2008) and the light variations were explained with a physically realistic star-spot model (Krtička et al 2007). Uniquely for an early-type chemically peculiar star, HD 37776 shows a complex double-wave longitudinal magnetic field variation (Thompson & Landstreet 1985), suggesting that its magnetic field topology significantly departs from an oblique dipolar field common for other Bp stars.…”

Section: Hd 37776mentioning

confidence: 96%

Magnetic Doppler imaging of early-type stars

et al. 2010

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Abstract. Doppler imaging of early-type magnetic stars is the most advanced method to interpret their line profile variations. DI allows us to study directly a complex interplay between chemical spots, magnetic fields, and the mass loss. Here we outline the general principles of the surface mapping of stars, discuss adaption of this technique to early-type stars and present several recent examples of the abundance and magnetic mapping performed for rapidly rotating early-B stars. In particular, we present the first Doppler images for the very fast rotating He-rich star HR 7355 and a reconstruction of magnetic field for the well-known Bp star σ Ori E. We also present new magnetic maps for the He-strong star HD 37776, which possesses one of the most complex magnetic field topologies among the upper main sequence stars.

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The light variability of the helium strong star HD 37776 as a result of its inhomogeneous elemental surface distribution

Cited by 75 publications

References 42 publications

Doppler imaging of the helium-variable star a Centauri

Doppler imaging of the helium-variable star a Centauri

Detection of a 1.59 h period in the B supergiant star HD 202850

Magnetic Doppler imaging of early-type stars

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