Magnetic Doppler imaging of the roAp star HD 24712

Lüftinger, T.; Kochukhov, O.; Ryabchikova, T. A.; Piskunov, Nikolai; Weiß, W. W.; Ilyin, I.

doi:10.1051/0004-6361/200811545

Cited by 74 publications

(103 citation statements)

References 30 publications

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“…Lüftinger et al 2010). In a strictly dipolar configuration such as the one we have considered, the simple diffusion model cannot reproduce such patterns.…”

Section: The Significance Of Bi-dimensional Resultsmentioning

confidence: 87%

Bi-dimensional element stratifications computed for magnetic Ap star atmospheres

Alecian¹,

Stift

2010

A&A

104

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Context. Theoretical modelling of abundance stratifications and surface distributions of chemical elements in Ap stars constitutes a major challenge. The atomic diffusion model provides the most appropriate framework in which to understand these abundance anomalies.Aims. We present theoretical 2D stratifications of 16 metals in upper main sequence chemically peculiar stars, with and without magnetic fields to provide a reference point for further theoretical and observational studies. Methods. We used our code CaratStrat to compute a large grid of stratifications (equilibrium solutions in LTE) for plane-parallel T eff = 8500, 10 000, 12 000, and 14 000 K stellar atmospheres. By interpolation, we constructed bi-dimensional cuts through these stellar atmospheres, which are permeated by a dipolar magnetic field of strength 20 kG at the magnetic pole. We also provide vertical (1D) stratifications of metals in non-magnetic stars (HgMn).Results. We present a large number of 2D and 1D stratifications, mostly as online material. We discuss in detail the case of Fe for the T eff = 8500 K model in the printed version, and compare it with stratifications derived from observed spectra.

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“…Lüftinger et al 2010). In a strictly dipolar configuration such as the one we have considered, the simple diffusion model cannot reproduce such patterns.…”

Section: The Significance Of Bi-dimensional Resultsmentioning

confidence: 87%

Bi-dimensional element stratifications computed for magnetic Ap star atmospheres

Alecian¹,

Stift

2010

A&A

104

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“…This inversion software represents a further development of the Invers10 code ), previously applied for mapping magnetic geometries and chemical spots on Ap stars (Kochukhov et al 2004;Kochukhov & Wade 2010;Lüftinger et al 2010). Both codes incorporate full treatment of the polarised radiative transfer using a modified diagonal element lambda-operator (DELO) algorithm (Rees et al 1989;.…”

Section: Zeeman Doppler Imaging Code Invers13mentioning

confidence: 99%

Magnetic field topology of the RS CVn star II Pegasi

Kochukhov

Mantere

Hackman

et al. 2013

A&A

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Context. The dynamo processes in cool active stars generate complex magnetic fields responsible for prominent surface stellar activity and variability at different time scales. For a small number of cool stars magnetic field topologies were reconstructed from the time series of spectropolarimetric observations using the Zeeman Doppler imaging (ZDI) method, often yielding surprising and controversial results. Aims. In this study we follow a long-term evolution of the magnetic field topology of the RS CVn binary star II Peg using a more self-consistent and physically more meaningful modelling approach compared to previous ZDI studies. Methods. We collected high-resolution circular polarisation observations of II Peg using the SOFIN spectropolarimeter at the Nordic Optical Telescope. These data cover 12 epochs spread over 7 years, comprising one of the most comprehensive spectropolarimetric data sets acquired for a cool active star. A multi-line diagnostic technique in combination with a new ZDI code is applied to interpret these observations. Results. We have succeeded in detecting clear magnetic field signatures in average Stokes V profiles for all 12 data sets. These profiles typically have complex shapes and amplitudes of ∼10 −3 of the unpolarised continuum, corresponding to mean longitudinal fields of 50-100 G. Magnetic inversions using these data reveals evolving magnetic fields with typical local strengths of 0.5-1.0 kG and complex topologies. Despite using a self-consistent magnetic and temperature mapping technique, we do not find a clear correlation between magnetic and temperature features in the ZDI maps. Neither do we confirm the presence of persistent azimuthal field rings found in other RS CVn stars. Reconstruction of the magnetic field topology of II Peg reveals significant evolution of both the surface magnetic field structure and the extended magnetospheric field geometry on the time scale covered by our observations. From 2004 to 2010 the total field energy drastically declined and the field became less axisymmetric. This also coincided with the transition from predominantly poloidal to mainly toroidal field topology. Conclusions. A qualitative comparison of the ZDI maps of II Peg with the prediction of dynamo theory suggests that the magnetic field in this star is produced mainly by the turbulent α 2 dynamo rather than the solar αΩ dynamo. Our results do not show a clear active longitude system, nor is there evidence of the presence of an azimuthal dynamo wave.

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“…The multipolar model field B mult , calculated by our code at each iteration, is equivalent to the dipole plus quadrupole parameterization of Bagnulo et al (1996). Stokes IV time series of the Ap stars α 2 CVn , HD 24712 (Lüftinger et al 2010) and HD 72106 (Folsom et al 2008) were interpreted using Invers10 in the multipolar regularization mode. All these studies inferred basically dipolar field geometries for the target stars.…”

Section: Magnetic Inversion Techniquementioning

confidence: 99%

Magnetic Doppler imaging ofα²Canum Venaticorum in all four Stokes parameters

Kochukhov¹,

Wade

2010

A&A

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114

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Context. Strong organized magnetic fields have been studied in the upper main sequence chemically peculiar stars for more than half a century. However, only recently have observational methods and numerical techniques become sufficiently mature to allow us to record and interpret high-resolution four Stokes parameter spectra, leading to the first assumption-free magnetic field models of these stars. Aims. Here we present a detailed magnetic Doppler imaging analysis of the spectropolarimetric observations of the prototypical magnetic Ap star α 2 CVn. This is the second star for which the magnetic field topology and horizontal chemical abundance inhomogeneities have been inferred directly from phase-resolved observations of line profiles in all four Stokes parameters, free from the traditional assumption of a low-order multipolar field geometry.Methods. We interpret the rotational modulation of the circular and linear polarization profiles of the strong Fe ii and Cr ii lines in the spectra of α 2 CVn recorded with the MuSiCoS spectropolarimeter. The surface abundance distributions of the two chemical elements and a full vector map of the stellar magnetic field are reconstructed in a self-consistent inversion using our state-of-the-art magnetic Doppler imaging code Invers10. Results. We succeeded in reproducing most of the details of the available spectropolarimetric observations of α 2 CVn with a magnetic map which combines a global dipolar-like field topology with localized spots of higher field intensity. We demonstrate that these small-scale magnetic structures are inevitably required to fit the linear polarization spectra; however, their presence cannot be inferred from the Stokes I and V observations alone. We also found high-contrast surface distributions of Fe and Cr, with both elements showing abundance minima in the region of weaker and topologically simpler magnetic field. Conclusions. Our magnetic Doppler imaging analysis of α 2 CVn and previous results for 53 Cam support the view that the upper main sequence stars can harbour fairly complex surface magnetic fields which resemble oblique dipoles only at the largest spatial scales. Spectra in all four Stokes parameters are absolutely essential to unveil and meaningfully characterize this field complexity in Ap stars. We therefore suggest that understanding magnetism of stars in other parts of the H-R diagram is similarly incomplete without investigation of their linear polarization spectra.

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Magnetic Doppler imaging of the roAp star HD 24712

Cited by 74 publications

References 30 publications

Bi-dimensional element stratifications computed for magnetic Ap star atmospheres

Bi-dimensional element stratifications computed for magnetic Ap star atmospheres

Magnetic field topology of the RS CVn star II Pegasi

Magnetic Doppler imaging ofα²Canum Venaticorum in all four Stokes parameters

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Magnetic Doppler imaging of the roAp star HD 24712

Cited by 74 publications

References 30 publications

Bi-dimensional element stratifications computed for magnetic Ap star atmospheres

Bi-dimensional element stratifications computed for magnetic Ap star atmospheres

Magnetic field topology of the RS CVn star II Pegasi

Magnetic Doppler imaging ofα2Canum Venaticorum in all four Stokes parameters

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Product

Resources

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Magnetic Doppler imaging ofα²Canum Venaticorum in all four Stokes parameters