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Kochukhov, Oleg
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Publications (10 of 201) Show all publications
Lavail, A., Kochukhov, O. & Wade, G. A. (2018). A sudden change of the global magnetic field of the active M dwarf AD Leo revealed by full Stokes spectropolarimetric observations. Monthly notices of the Royal Astronomical Society, 479(4), 4836-4843
Open this publication in new window or tab >>A sudden change of the global magnetic field of the active M dwarf AD Leo revealed by full Stokes spectropolarimetric observations
2018 (English)In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 479, no 4, p. 4836-4843Article in journal (Refereed) Published
Abstract [en]

In this paper we present an analysis of the first high-resolution full Stokes vector spectropolarimetric observations of the active M dwarf AD Leo. Based on observations collected in 2016 with the ESPaDOnS instrument at CFHT, we derived the least-squares deconvolved Stokes profiles and detected linear polarization signatures in spectral lines. At the same time, we discovered that the circular polarisation profiles corresponding to our data set are significantly weaker compared to all archival spectra of AD Leo, which exhibited approximately constant profiles over the time-scale of at least 6 yr until 2012. Magnetic maps obtained using Zeeman Doppler imaging confirm the sudden change in the surface magnetic field. Although the total magnetic field energy decreased by about 20 per cent between 2012 and 2016, the field component responsible for the observed circular polarization signatures corresponds to a stronger field occupying a smaller fraction of the stellar surface in the more recent map. These results represent the first evidence that active M dwarfs with dipole-dominated axisymmetric field topologies can undergo a long-term global magnetic variation.

National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-360239 (URN)10.1093/mnras/sty1825 (DOI)000441383700040 ()
Funder
Swedish National Space BoardSwedish Research CouncilKnut and Alice Wallenberg Foundation
Available from: 2018-09-11 Created: 2018-09-11 Last updated: 2018-10-12Bibliographically approved
Quitral-Manosalva, P., Cunha, M. S. & Kochukhov, O. (2018). A theoretical tool for the study of radial velocities in the atmospheres of roAp stars. Monthly Notices of the Royal Astronomical Society, 480(2), 1676-1688
Open this publication in new window or tab >>A theoretical tool for the study of radial velocities in the atmospheres of roAp stars
2018 (English)In: Monthly Notices of the Royal Astronomical Society, Vol. 480, no 2, p. 1676-1688Article in journal (Refereed) Published
Place, publisher, year, edition, pages
Oxford University Press (OUP), 2018
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-368683 (URN)10.1093/mnras/sty1935 (DOI)
Available from: 2018-12-06 Created: 2018-12-06 Last updated: 2018-12-06
Shultz, M., Rivinius, T., Wade, G. A., Alecian, E. & Kochukhov, O. (2018). HD 156324: A Tidally Locked Magnetic SB3 With an Orbitally Disrupted Centrifugal Magnetosphere. CONTRIBUTIONS OF THE ASTRONOMICAL OBSERVATORY SKALNATE PLESO, 48(1), 298-299
Open this publication in new window or tab >>HD 156324: A Tidally Locked Magnetic SB3 With an Orbitally Disrupted Centrifugal Magnetosphere
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2018 (English)In: CONTRIBUTIONS OF THE ASTRONOMICAL OBSERVATORY SKALNATE PLESO, ISSN 1335-1842, Vol. 48, no 1, p. 298-299Article in journal (Refereed) Published
Abstract [en]

Period analysis of radial velocity, equivalent width, and magnetic measurements of the SB3 system HD 156324 yield identical results in all cases, indicating the system is tidally locked with orbital and rotational periods of 1.58 d. Its H alpha emission profile exhibits marked morphological departures from the usual pattern observed amongst magnetic B-type stars, which can plausibly be ascribed to tidal disruption of the gravitocentrifugal potential.

Place, publisher, year, edition, pages
SLOVAK ACADEMY SCIENCES ASTRONOMICAL INST, 2018
Keywords
stars: individual: HD 156324, stars: magnetic field, binaries: spectroscopic, binaries (including multiple): close, stars: massive
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-357777 (URN)000432791300051 ()
Available from: 2018-08-22 Created: 2018-08-22 Last updated: 2018-08-22Bibliographically approved
Kochukhov, O., Johnston, C., Alecian, E. & Wade, G. A. (2018). HD66051: the first eclipsing binary hosting an early-type magnetic star. Monthly notices of the Royal Astronomical Society, 478(2), 1749-1762
Open this publication in new window or tab >>HD66051: the first eclipsing binary hosting an early-type magnetic star
2018 (English)In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 478, no 2, p. 1749-1762Article in journal (Refereed) Published
Abstract [en]

Early-type magnetic stars are rarely found in close binary systems. No such objects were known in eclipsing binaries prior to this study. Here we investigated the eclipsing, spectro-scopic double-lined binary HD66051, which exhibits out-of-eclipse photometric variations suggestive of surface brightness inhomogeneities typical of early-type magnetic stars. Using a new set of high-resolution spectropolarimetric observations, we discovered a weak magnetic field on the primary and found intrinsic, element-dependent variability in its spectral lines. The magnetic field structure of the primary is dominated by a nearly axisymmetric dipolar component with a polar field strength B-d approximate to 600G and an inclination with respect to the rotation axis of beta(d) = 13 degrees. A weaker quadrupolar component is also likely to be present. We combined the radial velocity measurements derived from our spectra with archival optical photometry to determine fundamental masses (3.16 and 1.75 M-circle dot) and radii (2.78 and 1.39 R-circle dot) with a 1-3 per cent precision. We also obtained a refined estimate of the effective temperatures (13000 and 9000 K) and studied chemical abundances for both components with the help of disentangled spectra. We demonstrate that the primary component of HD66051 is a typical late-B magnetic chemically peculiar star with a non-uniform surface chemical abundance distribution. It is not an HgMn-type star as suggested by recent studies. The secondary is a metallic-line star showing neither a strong, global magnetic field nor intrinsic spectral variability. Fundamental parameters provided by our work for this interesting system open unique possibilities for probing interior structure, studying atomic diffusion, and constraining binary star evolution.

Place, publisher, year, edition, pages
Oxford University Press, 2018
Keywords
binaries: eclipsing, stars: chemically peculiar, stars: fundamental parameters, stars: individual: HD66051 (V414 Pup), stars: magnetic field
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-362046 (URN)10.1093/mnras/sty1118 (DOI)000439547400022 ()
Funder
Knut and Alice Wallenberg FoundationSwedish Research CouncilEU, European Research Council, 670519: MAMSIE
Available from: 2018-10-11 Created: 2018-10-11 Last updated: 2018-12-11
Rusomarov, N., Kochukhov, O. & Lundin, A. (2018). Magnetic field topology and chemical spot distributions of the Ap star HD 119419. Astronomy and Astrophysics, 609, Article ID A88.
Open this publication in new window or tab >>Magnetic field topology and chemical spot distributions of the Ap star HD 119419
2018 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 609, article id A88Article in journal (Refereed) Published
Abstract [en]

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 full Stokes vector observations of the magnetic Ap star HD 119419 – a 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 (MDI) 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, MDI studies of cluster members will allow us to study the field topologies and chemical abundance spots as a function of stellar age.

Keywords
stars: chemically peculiar, stars: atmospheres, stars: individual: HD 119419, stars: magnetic field
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-343856 (URN)10.1051/0004-6361/201731914 (DOI)000423434200006 ()
Funder
Knut and Alice Wallenberg FoundationSwedish Research CouncilSwedish National Space Board
Available from: 2018-03-02 Created: 2018-03-02 Last updated: 2018-03-02Bibliographically approved
Rosén, L., Kochukhov, O., Alecian, E., Neiner, C., Morin, J. & Wade, G. A. (2018). Magnetic field topology of the cool, active, short-period binary system sigma(2) Coronae Borealis. Astronomy and Astrophysics, 613, Article ID A60.
Open this publication in new window or tab >>Magnetic field topology of the cool, active, short-period binary system sigma(2) Coronae Borealis
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2018 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 613, article id A60Article in journal (Refereed) Published
Abstract [en]

Aims. The goal of this work is to study the cool, active binary star sigma(2) CrB, focussing on its magnetic field. The two F9-G0 components of this system are tidally locked and in a close orbit, increasing the chance of interaction between their magnetospheres. Methods. We used Stokes IV data from the twin spectropolarimeters Narval at the TBL and ESPaDOnS at the CFHT. The leastsquares deconvolution multi-line technique was used to increase the signal-to-noise ratio of the data. We then applied a new binary Zeeman-Doppler imaging code to reconstruct simultaneously the magnetic topology and brightness distribution of both components of sigma(2) CrB. This analysis was carried out for two observational epochs in 2014 and 2017. Results. A previously unconfirmed magnetic field of the primary star has been securely detected. At the same time, the polarisation signatures of the secondary appear to have a systematically larger amplitude than that of the primary. This corresponds to a stronger magnetic field, for which the magnetic energy of the secondary exceeds that of the primary by a factor of 3.3-5.7. While the magnetic energy is similar for the secondary star in the two epochs, the magnetic energy is about twice as high in 2017 for the primary. The magnetic field topology of the two stars in the earlier epoch (2014) is very different. The fractions of energy in the dipole and quadrupole components of the secondary are similar and thereafter decrease with increasing harmonic angular degree l. At the same time, for the primary the fraction of energy in the dipole component is low and the maximum energy contribution comes from l = 4. However, in the 2017 epoch both stars have similar field topologies and a systematically decreasing energy with increasing l. In the earlier epoch, the magnetic field at the visible pole appears to be of opposite polarity for the primary and secondary, suggesting linked magnetospheres. The apparent rotational periods of both sigma(2) CrB components are longer than the orbital period, which we interpret as an evidence of a solar-like differential rotation. Conclusions. Despite their nearly identical fundamental parameters, the components of sigma(2) CrB system exhibit different magnetic field properties. This indicates that the magnetic dynamo process is a very sensitive function of stellar parameters.

Place, publisher, year, edition, pages
EDP Sciences, 2018
Keywords
polarization, stars: activity, stars: magnetic field, stars: late-type, stars: individual: sigma(2) CrB
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-357716 (URN)10.1051/0004-6361/201731706 (DOI)000433880200006 ()
Funder
Swedish Research CouncilKnut and Alice Wallenberg FoundationEU, Horizon 2020, ANR10 LABX56
Available from: 2018-08-31 Created: 2018-08-31 Last updated: 2018-12-11
Farihi, J., Fossati, L., Wheatley, P. J., Metzger, B. D., Mauerhan, J., Bachman, S., . . . Stone, N. (2018). Magnetism, X-rays and accretion rates in WD 1145+017 and other polluted white dwarf systems. Monthly notices of the Royal Astronomical Society, 474(1), 947-960
Open this publication in new window or tab >>Magnetism, X-rays and accretion rates in WD 1145+017 and other polluted white dwarf systems
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2018 (English)In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 474, no 1, p. 947-960Article in journal (Refereed) Published
Abstract [en]

This paper reports circular spectropolarimetry and X-ray observations of several polluted white dwarfs including WD 1145+017, with the aim to constrain the behaviour of disc material and instantaneous accretion rates in these evolved planetary systems. Two stars with previously observed Zeeman splitting, WD 0322-019 and WD 2105-820, are detected above 5 sigma and < B-z > > 1 kG, while WD 1145+017, WD 1929+011, and WD 2326+049 yield (null) detections below this minimum level of confidence. For these latter three stars, high-resolution spectra and atmospheric modelling are used to obtain limits on magnetic field strengths via the absence of Zeeman splitting, finding B-* < 20 kG based on data with resolving power R approximate to 40 000. An analytical framework is presented for bulk Earth composition material falling on to the magnetic polar regions of white dwarfs, where X-rays and cyclotron radiation may contribute to accretion luminosity. This analysis is applied to X-ray data for WD 1145+017, WD 1729+371, and WD 2326+049, and the upper bound count rates are modelled with spectra for a range of plasma kT = 1-10 keV in both the magnetic and non-magnetic accretion regimes. The results for all three stars are consistent with a typical dusty white dwarf in a steady state at 108-109 g s(-1). In particular, the non-magnetic limits for WD 1145+017 are found to be well below previous estimates of up to 10(12) g s(-1), and likely below 1010 g s(-1), thus suggesting the star-disc system may be average in its evolutionary state, and only special in viewing geometry.

Place, publisher, year, edition, pages
OXFORD UNIV PRESS, 2018
Keywords
circumstellar matter, stars: magnetic field, planetary systems, white dwarfs, X-rays: stars
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-348400 (URN)10.1093/mnras/stx2664 (DOI)000424339500070 ()
Available from: 2018-04-12 Created: 2018-04-12 Last updated: 2018-04-12Bibliographically approved
Oksala, M. E., Silvester, J., Kochukhov, O., Neiner, C. & Wade, G. A. (2018). Mixed poloidal-toroidal magnetic configuration and surface abundance distributions of the Bp star 36 Lyn. Monthly notices of the Royal Astronomical Society, 473(3), 3367-3376
Open this publication in new window or tab >>Mixed poloidal-toroidal magnetic configuration and surface abundance distributions of the Bp star 36 Lyn
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2018 (English)In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 473, no 3, p. 3367-3376Article in journal (Refereed) Published
Abstract [en]

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, B, using the multiline least-squares deconvolution (LSD) technique. A rotationally phased B 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.

Keywords
techniques: polarimetric, techniques: spectroscopic, stars: chemically peculiar, stars: individual: 36 Lyn
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-346360 (URN)10.1093/mnras/stx2487 (DOI)000423809400040 ()
Funder
Knut and Alice Wallenberg FoundationSwedish Research CouncilGöran Gustafsson Foundation for promotion of scientific research at Uppala University and Royal Institute of Technology
Available from: 2018-03-23 Created: 2018-03-23 Last updated: 2018-03-23Bibliographically approved
Kochukhov, O. & Ryabchikova, T. A. (2018). Putting atomic diffusion theory of magnetic ApBp stars to the test: evaluation of the predictions of time-dependent diffusion models. Monthly notices of the Royal Astronomical Society, 474(2), 2787-2795
Open this publication in new window or tab >>Putting atomic diffusion theory of magnetic ApBp stars to the test: evaluation of the predictions of time-dependent diffusion models
2018 (English)In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 474, no 2, p. 2787-2795Article in journal (Refereed) Published
Abstract [en]

A series of recent theoretical atomic diffusion studies has address the challenging problem of predicting inhomogeneous vertical and horizontal chemical element distributions in the atmospheres of magnetic ApBp stars. Here we critically assess the most sophisticated of such diffusion models - based on a time-dependent treatment of the atomic diffusion in a magnetized stellar atmosphere - by direct comparison with observations as well by testing the widely used surface mapping tools with the spectral line profiles predicted by this theory. We show that the mean abundances of Fe and Cr are grossly underestimated by the time-dependent theoretical diffusion model, with discrepancies reaching a factor of 1000 for Cr. We also demonstrate that Doppler imaging inversion codes, based either on modelling of individual metal lines or line-averaged profiles simulated according to theoretical three-dimensional abundance distribution, are able to reconstruct correct horizontal chemical spot maps despite ignoring the vertical abundance variation. These numerical experiments justify a direct comparison of the empirical two-dimensional Doppler maps with theoretical diffusion calculations. This comparison is generally unfavourable for the current diffusion theory, as very few chemical elements are observed to form overabundance rings in the horizontal field regions as predicted by the theory and there are numerous examples of element accumulations in the vicinity of radial field zones, which cannot be explained by diffusion calculations.

Place, publisher, year, edition, pages
OXFORD UNIV PRESS, 2018
Keywords
diffusion, line: profiles, stars: abundances, stars: chemically peculiar
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-348401 (URN)10.1093/mnras/stx2961 (DOI)000424343600096 ()
Funder
Knut and Alice Wallenberg FoundationSwedish Research CouncilSwedish National Space Board
Available from: 2018-04-12 Created: 2018-04-12 Last updated: 2018-04-12Bibliographically approved
Shultz, M., Wade, G. A., Rivinius, T., Neiner, C., Kochukhov, O. & Alecian, E. (2018). Rotation, Emission, & Evolution of the Magnetic Early B-type Stars. CONTRIBUTIONS OF THE ASTRONOMICAL OBSERVATORY SKALNATE PLESO, 48(1), 175-179
Open this publication in new window or tab >>Rotation, Emission, & Evolution of the Magnetic Early B-type Stars
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2018 (English)In: CONTRIBUTIONS OF THE ASTRONOMICAL OBSERVATORY SKALNATE PLESO, ISSN 1335-1842, Vol. 48, no 1, p. 175-179Article in journal (Refereed) Published
Abstract [en]

We report the results of the first population study of 51 magnetic early B-type stars, based upon a large database of high-resolution spectropolarimetry assembled by the MiMeS and BinaMIcS collaborations. Utilizing these data, rotational periods were determined for all but 5 of the sample stars. This enabled us to determine dipole oblique rotator model parameters, rotational parameters, and magnetospheric parameters. We find that the ratio of the Alfven radius to the Kepler corotation radius is highly predictive of whether or not a star displays Ha emission from a Centrifugal Magnetosphere (CM), as expected from theoretical considerations. We also find that CM host stars are systematically younger than the general population, as expected given that CM emission requires rapid rotation and a strong magnetic field, and a strong magnetic field will lead to rapid magnetic braking. We conclude that emission-line magnetic early B-type stars are, almost without exception, strongly magnetized, rapidly rotating, and young.

Place, publisher, year, edition, pages
SLOVAK ACADEMY SCIENCES ASTRONOMICAL INST, 2018
Keywords
stars: magnetic field, stars: rotation, stars: early-type, stars: evolution, stars: massive
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-357775 (URN)000432791300024 ()
Available from: 2018-08-22 Created: 2018-08-22 Last updated: 2018-08-22Bibliographically approved
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