Magnetic Doppler imaging of the chemically peculiar star HD 125248

Rusomarov, N.; Kochukhov, O.; Ryabchikova, T. A.; Ilyin, I.

doi:10.1051/0004-6361/201527719

Cited by 25 publications

(30 citation statements)

References 54 publications

(92 reference statements)

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“…In this paper we present a model atmosphere analysis as well as a detailed study of the surface magnetic and chemical structure for the magnetic Ap star HD 119419. This investigation extends our series of four Stokes parameter magnetic mapping studies (Kochukhov et al, 2004;Kochukhov & Wade, 2010;Silvester et al, 2014Silvester et al, , 2015Silvester et al, , 2017Rusomarov et al, 2015Rusomarov et al, , 2016 to a late-B chemically peculiar star which is a member of an open cluster and therefore has a well-established age.…”

Section: Discussionsupporting

confidence: 55%

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Magnetic field topology and chemical spot distributions of the Ap star HD 119419

Rusomarov¹,

Kochukhov²,

Lundin³

2018

A&A

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Context. Analysis of high-resolution spectropolarimetric time-series observations of early-type magnetic stars is currently the most advanced method of obtaining detailed information on their surface magnetic field topologies and horizontal spot distributions. Aims. In this study we analyse a new set of high-quality four Stokes parameter observations of the magnetic Ap star HD 119419a member of the 14 Myr old Lower Cen-Cru association -for the purpose of studying the surface field topology and mapping the chemical abundance spots. Methods. We made use of the circular and linear polarisation data collected for HD 119419 with the HARPSpol instrument at the ESO 3.6-m telescope. These observations were analysed with a multi-line magnetic diagnostic technique and modelled in detail with a Magnetic Doppler imaging code. Results. We present a new set of high-precision mean longitudinal magnetic field measurements and derive a revised stellar rotational period by comparing our measurements with the literature data. We also redetermine the basic stellar atmospheric parameters. Our four Stokes parameter magnetic inversions reveal a moderately complex surface field topology with a mean field strength of 18 kG and a maximum local strength of 24 kG. A poloidal dipolar component dominates the magnetic energy spectrum of the surface field in HD 119419. However, significant contributions of the higher-order spherical harmonic components are also present. We show that the dipole plus quadrupole part of the reconstructed field geometry is incapable of reproducing the observed amplitudes and shapes of the Stokes Q and U profiles. The chemical abundance distributions of Fe, Cr, Ti, and Nd, derived self-consistently with the magnetic field geometry, are characterised by large abundance gradients and a lack of clear correlation with the magnetic field structure. Conclusions. This full Stokes vector analysis of HD 119419 extends the modern hot-star magnetic mapping investigations to an open cluster Ap star with a well-determined age. Further Magnetic Doppler imaging studies of cluster members will allow us to study the field topologies and chemical abundance spots as a function of stellar age.

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Section: Discussionsupporting

confidence: 55%

“…This paper follows the same methodology of the magnetic inversions as was repeatedly applied by previous similar MDI studies (e.g. Silvester et al, 2014;Rusomarov et al, 2015Rusomarov et al, , 2016.…”

Section: Surface Mapping Methodologymentioning

confidence: 99%

Magnetic field topology and chemical spot distributions of the Ap star HD 119419

Rusomarov¹,

Kochukhov²,

Lundin³

2018

A&A

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“…90% of the magnetic field energy is in the first harmonic (ℓ = 1), confirming that the field geometry is primarily dipolar. However, the dipolar (ℓ = 1) harmonic has a large toroidal component (36%); this is a much larger contribution than has been observed to date in other Ap/Bp stars that have been mapped with a similar method (e.g., Kochukhov et al 2014;Rusomarov et al 2015Rusomarov et al , 2016Silvester et al 2015). This toroidal component can also be identified in the vector field map in Fig.…”

Section: Magnetic Field Structurementioning

confidence: 70%

Mixed poloidal–toroidal magnetic configuration and surface abundance distributions of the Bp star 36 Lyn★

Oksala

Silvester

Kochukhov

et al. 2017

Monthly Notices of the Royal Astronomical Society

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Previous studies of the chemically peculiar Bp star 36 Lyn revealed a moderately strong magnetic field, circumstellar material and inhomogeneous surface abundance distributions of certain elements. We present in this paper an analysis of 33 high signal-to-noise ratio, high-resolution Stokes IV observations of 36 Lyn obtained with the Narval spectropolarimeter at the Bernard Lyot Telescope at Pic du Midi Observatory. From these data, we compute new measurements of the mean longitudinal magnetic field, Bℓ, using the multiline least-squares deconvolution (LSD) technique. A rotationally phased Bℓ curve reveals a strong magnetic field, with indications for deviation from a pure dipole field. We derive magnetic maps and chemical abundance distributions from the LSD profiles, produced using the Zeeman–Doppler imaging code InversLSD. Using a spherical harmonic expansion to characterize the magnetic field, we find that the harmonic energy is concentrated predominantly in the dipole mode (ℓ = 1), with significant contribution from both the poloidal and toroidal components. This toroidal field component is predicted theoretically, but not typically observed for Ap/Bp stars. Chemical abundance maps reveal a helium enhancement in a distinct region where the radial magnetic field is strong. Silicon enhancements are located in two regions, also where the radial field is stronger. Titanium and iron enhancements are slightly offset from the helium enhancements, and are located in areas where the radial field is weak, close to the magnetic equator.

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“…Several recent studies took advantage of the magnetic DI (MDI, Piskunov & Kochukhov 2002) extension of the indirect mapping technique to recover self-consistently magnetic field topologies and chemical spot distributions from the variation of Stokes parameter spectra (e.g. Kochukhov et al 2015;Silvester et al 2015;Rusomarov et al 2016). However, only a few stars were analysed with this sophisticated MDI method; most observational constraints on the chemical element distributions are still provided by non-magnetic DI investigations.…”

Section: Introductionmentioning

confidence: 99%

Doppler imaging of chemical spots on magnetic Ap/Bp stars

Kochukhov

2016

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Context. Doppler imaging (DI) is a powerful spectroscopic inversion technique that enables conversion of a line profile time series into a two-dimensional map of the stellar surface inhomogeneities. DI has been repeatedly applied to reconstruct chemical spot topologies of magnetic Ap/Bp stars with the goal of understanding variability of these objects and gaining an insight into the physical processes responsible for spot formation. Aims. In this paper we investigate the accuracy of chemical abundance DI and assess the impact of several different systematic errors on the reconstructed spot maps. Methods. We have simulated spectroscopic observational data for two different Fe spot distributions with a surface abundance contrast of 1.5 dex in the presence of a moderately strong dipolar magnetic field. We then reconstructed chemical maps using different sets of spectral lines and making different assumptions about line formation in the inversion calculations. Results. Our numerical experiments demonstrate that a modern DI code successfully recovers the input chemical spot distributions comprised of multiple circular spots at different latitudes or an element overabundance belt at the magnetic equator. For the optimal reconstruction based on half a dozen spectral intervals, the average reconstruction errors do not exceed ∼0.10 dex. The errors increase to about 0.15 dex when abundance distributions are recovered from a few and/or blended spectral lines. Ignoring a 2.5 kG dipolar magnetic field in chemical abundance DI leads to an average relative error of 0.2 dex and maximum errors of 0.3 dex. Similar errors are encountered if a DI inversion is carried out neglecting a non-uniform continuum brightness distribution and variation of the local atmospheric structure. None of the considered systematic effects lead to major spurious features in the recovered abundance maps.Conclusions. This series of numerical DI simulations proves that inversions based on one or two spectral lines with simplifying assumptions of the non-magnetic radiative transfer and a single model atmosphere are generally reliable provided that the stellar magnetic field is not much stronger than 2-3 kG and the recovered spot map has a contrast of at least ∼0.3 dex. In the light of these findings, we assess magnetic field strengths of several dozen Ap/Bp stars previously studied with DI methods, concluding that the vast majority of the published chemical spot maps are unaffected by the systematic errors addressed in this paper.

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Magnetic Doppler imaging of the chemically peculiar star HD 125248

Cited by 25 publications

References 54 publications

Magnetic field topology and chemical spot distributions of the Ap star HD 119419

Magnetic field topology and chemical spot distributions of the Ap star HD 119419

Mixed poloidal–toroidal magnetic configuration and surface abundance distributions of the Bp star 36 Lyn★

Doppler imaging of chemical spots on magnetic Ap/Bp stars

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