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

Rusomarov, N.; Kochukhov, O.; Ryabchikova, T. A.; Piskunov, Nikolai

doi:10.1051/0004-6361/201424559

Cited by 29 publications

(44 citation statements)

References 30 publications

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“…These four stars are young objects with masses between 2.3 and 3.1 M . Rusomarov et al (2015) found a dipole field for HD 24712, which has a mass of 1.55 M and is likely to be much older than the other stars. Thus, it appears that our finding of magnetic field for HD 125248, which is significantly more complex than a dipole, supports the hypothesis that old (or less massive) Ap stars have predominantly dipolar fields with little structure on small scales.…”

Section: Summary and Discussionmentioning

confidence: 93%

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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: Summary and Discussionmentioning

confidence: 93%

“…We performed this task with the MDI code invers10 introduced by and . In this study, we closely follow already established methodological practices that have been used in recent MDI studies (e.g., Rusomarov et al 2015;Kochukhov et al 2015).…”

Section: Methodsmentioning

confidence: 99%

Magnetic Doppler imaging of the chemically peculiar star HD 125248

Rusomarov

Kochukhov

Ryabchikova

et al. 2016

A&A

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“…For example, the full Stokes vector studies of bright Ap stars α 2 CVn and 53 Cam discovered small-scale horizontal contributions on top of large-scale dipole-like fields (Kochukhov et al 2004a;Kochukhov & Wade 2010;Silvester et al 2014). On the other hand, the four Stokes parameter analysis of the cool Ap star HD 24712 (Rusomarov et al 2015) found no significant departures from a purely dipolar topology.…”

Section: Introductionmentioning

confidence: 99%

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

Kochukhov

Rusomarov

Valenti

et al. 2015

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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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“…Our poor (u, v) plane coverage prevents us from analyzing the angular diameter variation with respect to the baseline orientation, which is not penalizing since HD 24712 is a very slow rotator, as are Ap stars in general. Its v sin i is quoted to be 18 km s −1 in Royer et al (2002) and, more recently, 5.8 km s −1 in Glebocki & Gnacinski (2005), and its inclination i equals 120 • (Rusomarov et al 2015), therefore no photosphere flattening is expected to be detectable. Our radius estimation is thus not biased by the rotational effect.…”

Section: Chara/vega Observationsmentioning

confidence: 87%

“…Like all the Ap stars, it exhibits a strong large-scale organized magnetic field whose intensity is changing as the star rotates with a period of 12.46 days (Lüftinger et al 2008). The recent study of Rusomarov et al (2015) concludes that the magnetic field topology of HD 24712 has a dominant dipolar component with a very weak contribution from high orders. The authors derive a polar field strength B p = 3440 G, an inclination angle between the line of sight and the stellar rotation axis of i = 120 • , and an angle between the magnetic and rotation axes of β = 160 • .…”

Section: Introductionmentioning

confidence: 99%

The fundamental parameters of the roAp star HD 24712

Perraut

Brandão

Cunha

et al. 2016

A&A

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Context. There is still a debate about the nature of the mechanism that causes the pulsation excitation of the rapidly oscillating Ap stars that oscillate above the highest theoretically acoustic frequency. HD 24712 is a good test case for such a study because it is bright, its parallax accurately determined, and its frequency spectrum is well known. Aims. Visible long-baseline interferometry is a unique technique for measuring accurate angular diameters of targets as small as the brightest roAp stars, and thus estimating accurate radii by a method as independent as possible of atmosphere models. Methods. We used the visible spectrograph VEGA at the CHARA long-baseline optical array to observe HD 24712, and we derived its limb-darkened diameter. We also estimated its bolometric flux from spectroscopic data in the literature and determined its radius, luminosity, and effective temperature. Results. We determined a limb-darkened angular diameter of 0.335 ± 0.009 mas for HD 24712 and derived a radius of R = 1.772 ± 0.057 R , a luminosity of L = 7.2 ± 1.8 L , and an effective temperature of T eff = 7235 ± 280 K, which is in very close agreement with the values provided by the self-consistent stratified model developed for this star. We used these fundamental parameters to set HD 24712 in the Hertzsprung-Russell diagram. Its position is marginally consistent with the region where high radial order modes are predicted to be excited by the κ-mechanism. Conclusions. We conclude that oscillations in this star are most likely not driven by the κ-mechanism.

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

Cited by 29 publications

References 30 publications

Magnetic Doppler imaging of the chemically peculiar star HD 125248

Magnetic Doppler imaging of the chemically peculiar star HD 125248

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

The fundamental parameters of the roAp star HD 24712

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