Three-dimensional magnetic and abundance mapping of the cool Ap star HD 24712

Rusomarov, N.; Kochukhov, O.; Piskunov, Nikolai; Jeffers, S. V.; Johns–Krull, Christopher M.; Keller, Christoph U.; Makaganiuk, V.; Rodenhuis, M.; Snik, Frans; Stempels, H. C.; Valenti, Jeff A.

doi:10.1051/0004-6361/201220950

Cited by 28 publications

(26 citation statements)

References 60 publications

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“…The net linear polarization is calculated from the equivalent width of the LSD Stokes Q and U profiles and contains information about the transverse component of the magnetic field that is similar to what is diagnosed by the broadband linear polarization (Leroy 1995). However, direct comparison between the two types of measurements is not possible unless they are scaled and shifted (e.g., Wade et al 2000;Rusomarov et al 2013).…”

Section: Integral Magnetic Observablesmentioning

confidence: 99%

Magnetic Doppler imaging of the chemically peculiar star HD 125248

Rusomarov

Kochukhov

Ryabchikova

et al. 2016

A&A

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Context. Intermediate-mass, chemically peculiar stars with strong magnetic fields provide an excellent opportunity to study the topology of their surface magnetic fields and the interplay between magnetic geometries and abundance inhomogeneities in the atmospheres of these stars. Aims. We reconstruct detailed maps of the surface magnetic field and abundance distributions for the magnetic Ap star HD 125248. Methods. We performed the analysis based on phase-resolved, four Stokes parameter spectropolarimetric observations obtained with the HARPSpol instrument. These data were interpreted with the help of magnetic Doppler imaging techniques and model atmospheres taking the effects of strong magnetic fields and nonsolar chemical composition into account. Results. We improved the atmospheric parameters of the star, T eff = 9850 ± 250 K and log g = 4.05 ± 0.10. We performed detailed abundance analysis, which confirmed that HD 125248 has abundances typical of other Ap stars, and discovered significant vertical stratification effects for the Fe ii and Cr ii ions. We computed LSD Stokes profiles using several line masks corresponding to Fepeak and rare earth elements, and studied their behavior with rotational phase. Combining previous longitudinal field measurements with our own observations, we improved the rotational period of the star P rot = 9.29558 ± 0.00006 d. Magnetic Doppler imaging of HD 125248 showed that its magnetic field is mostly poloidal and quasi-dipolar with two large spots of different polarity and field strength. The chemical maps of Fe, Cr, Ce, Nd, Gd, and Ti show abundance contrasts of 0.9-3.5 dex. Among these elements, the Fe abundance map does not show high-contrast features. Cr is overabundant around the negative magnetic pole and has 3.5 dex abundance range. The rare earth elements and Ti are overabundant near the positive magnetic pole. Conclusions. The magnetic field of HD 125248 has strong deviations from the classical oblique dipole field geometry. A comparison of the magnetic field topology of HD 125248 with the results derived for other stars using four Stokes magnetic Doppler imaging suggests evidence that the field topology becomes simpler with increasing age. The abundance maps show weak correlation with magnetic field geometry, but they do not agree with the theoretical atomic diffusion calculations, which predict element accumulation in the horizontal field regions.

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Section: Integral Magnetic Observablesmentioning

confidence: 99%

Magnetic Doppler imaging of the chemically peculiar star HD 125248

Rusomarov

Kochukhov

Ryabchikova

et al. 2016

A&A

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“…Each polarimetric observation (except for the observation taken on 31-05-2009) was obtained by acquiring four successive individual spectra with the quarterwave plate rotated in such a way to acquire the desired Stokes spectrum (see e.g. Rusomarov et al 2013, for further details).…”

Section: Observationsmentioning

confidence: 99%

A comprehensive analysis of the magnetic standard star HD 94660: Host of a massive compact companion?

Bailey

Grunhut²,

Landstreet

2015

A&A

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Aims. Detailed information about the magnetic geometry, atmospheric abundances and radial velocity variations has been obtained for the magnetic standard star HD 94660 based on high-dispersion spectroscopic and spectropolarimetric observations from the UVES, HARPSpol and ESPaDOnS instruments. Methods. We perform a detailed chemical abundance analysis using the spectrum synthesis code ZEEMAN for a total of 17 elements. Using both line-of-sight and surface magnetic field measurements, we derive a simple magnetic field model that consists of dipole, quadrupole and octupole components. Results. The observed magnetic field variations of HD 94660 are complex and suggest an inhomogeneous distribution of chemical elements over the stellar surface. This inhomogeneity is not reflected in the abundance analysis, from which all available spectra are modelled, but only a mean abundance is reported for each element. The derived abundances are mostly non-solar, with striking overabundances of Fe-peak and rare-earth elements. Of note are the clear signatures of vertical chemical stratification throughout the stellar atmosphere, most notably for the Fe-peak elements. We also report on the detection of radial velocity variations with a total range of 35 km s −1 in the spectra of HD 94660. A preliminary analysis shows the most likely period of these variations to be of order 840 d and, based on the derived orbital parameters of this star, suggests the first detection of a massive compact companion for a main sequence magnetic star. Conclusions. HD 94660 exhibits interestingly complex magnetic field variations and remarkable radial velocity variations. Long term monitoring is necessary to provide further constraints on the nature of these radial velocity variations. Detection of a companion will help establish the role of binarity in the origin of magnetism in stars with radiative envelopes.

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“…A detailed account of the HARPSpol observing procedures and the key steps of data reduction, such as the optimal extraction of échelle spectra and calculation of the Stokes parameters from a sequence of polarimetric sub-exposures, was given by Rusomarov et al (2013). In the present paper we use the exact same observing procedures and reduction techniques.…”

Section: Observational Datamentioning

confidence: 99%

Magnetic field topology and chemical spot distributions in the extreme Ap star HD 75049

Kochukhov

Rusomarov

Valenti

et al. 2015

A&A

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Context. Intermediate-mass, magnetic chemically peculiar (Ap) stars provide a unique opportunity to study the topology of stellar magnetic fields in detail and to investigate magnetically driven processes of spot formation. Aims. Here we aim to derive the surface magnetic field geometry and chemical abundance distributions for the extraordinary Ap star HD 75049. This object hosts a surface field of ∼30 kG, one of the strongest known for any non-degenerate star. Methods. We used time-series of high-resolution HARPS intensity and circular polarisation observations. These data were interpreted with the help of magnetic Doppler imaging and model atmospheres incorporating effects of a non-solar chemical composition and a strong magnetic field. Results. Based on high-precision measurements of the mean magnetic field modulus, we refined the rotational period of HD 75049 to P rot = 4.048267 ± 0.000036 d. We also derived basic stellar parameters, T eff = 10 250 ± 250 K and log g = 4.3 ± 0.1. Magnetic Doppler imaging revealed that the field topology of HD 75049 is poloidal and dominated by a dipolar contribution with a peak surface field strength of 39 kG. At the same time, deviations from the classical axisymmetric oblique dipolar configuration are significant. Chemical surface maps of Si, Cr, Fe, and Nd show abundance contrasts of 0.5-1.4 dex, which is low compared with many other Ap stars. Of the chemical elements, Nd is found to be enhanced close to the magnetic pole, whereas Si and Cr are concentrated predominantly at the magnetic equator. The iron distribution shows low-contrast features both at the magnetic equator and the pole. Conclusions. The morphology of the magnetic field and the properties of chemical spots in HD 75049 are qualitatively similar to those of Ap stars with weaker fields. Consequently, whatever mechanism forms and sustains global magnetic fields in intermediatemass main-sequence stars, it operates in the same way over the entire observed range of magnetic field strengths.

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Three-dimensional magnetic and abundance mapping of the cool Ap star HD 24712

Cited by 28 publications

References 60 publications

Magnetic Doppler imaging of the chemically peculiar star HD 125248

Magnetic Doppler imaging of the chemically peculiar star HD 125248

A comprehensive analysis of the magnetic standard star HD 94660: Host of a massive compact companion?

Magnetic field topology and chemical spot distributions in the extreme Ap star HD 75049

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