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Shultz, Matthew
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Publications (10 of 13) Show all publications
Kochukhov, O., Shultz, M. & Neiner, C. (2019). Magnetic field topologies of the bright, weak-field Ap stars θ Aurigae and ε Ursae Majoris. Astronomy and Astrophysics, 621, 1-18, Article ID A47.
Open this publication in new window or tab >>Magnetic field topologies of the bright, weak-field Ap stars θ Aurigae and ε Ursae Majoris
2019 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 621, p. 1-18, article id A47Article in journal (Refereed) Published
Abstract [en]

Context. The brightest magnetic chemically peculiar stars theta Aur and epsilon UMa were targeted by numerous studies of their photometric and spectroscopic variability. Detailed maps of chemical abundance spots were repeatedly derived for both stars. However, owing to the weakness of their surface magnetic fields, very little information on the magnetic field geometries of these stars is available.

Aims. In this study we aim to determine detailed magnetic field topologies of theta Aur and epsilon UMa based on modern, high-resolution spectropolarimetric observations.

Methods. Both targets were observed in all four Stokes parameters using the Narval and ESPaDOnS spectropolarimeters. A multi-line technique of least-squares deconvolution was employed to detect polarisation signatures in spectral lines. These signatures were modelled with a Zeeman-Doppler imaging code.

Results. We succeed in detecting variable circular and linear polarisation signatures for theta Aur. Only circular polarisation was detected for epsilon UMa. We obtain new sets of high-precision longitudinal magnetic field measurements using mean circular polarisation metal line profiles as well as hydrogen line cores, which are consistent with historical data. Magnetic inversions revealed distorted dipolar geometries in both stars. The Fe and Cr abundance distributions, reconstructed simultaneously with magnetic mapping, do not show a clear correlation with the local magnetic field properties, with the exception of a relative element underabundance in the horizontal field regions along the magnetic equators.

Conclusions. Our study provides the first ever detailed surface magnetic field maps for broad-line, weak-field chemically peculiar stars, showing that their field topologies are qualitatively similar to those found in stronger field stars. The Fe and Cr chemical abundance maps reconstructed for theta Aur and epsilon UMa are at odds with the predictions of current theoretical atomic diffusion calculations.

Keywords
stars: atmospheres, stars: chemically peculiar, stars: magnetic field, starspots, stars: individual: theta Aur, stars: individual: epsilon UMa
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-374427 (URN)10.1051/0004-6361/201834279 (DOI)000454877000001 ()
Funder
Swedish Research Council, 621-2014-5720Swedish National Space Board, 185/14Swedish National Space Board, 137/17
Available from: 2019-01-28 Created: 2019-01-28 Last updated: 2019-01-28Bibliographically approved
Shultz, M., Le Bouquin, J.-B. -., Rivinius, T., Wade, G. A., Kochukhov, O., Alecian, E., . . . Lacour, S. (2019). NU Ori: a hierarchical triple system with a strongly magnetic B-type star. Monthly notices of the Royal Astronomical Society, 482(3), 3950-3965
Open this publication in new window or tab >>NU Ori: a hierarchical triple system with a strongly magnetic B-type star
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2019 (English)In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 482, no 3, p. 3950-3965Article in journal (Refereed) Published
Abstract [en]

NU Ori is a massive spectroscopic and visual binary in the Orion Nebula Cluster, with four components: Aa, Ab, B, and C. The B0.5 primary (Aa) is one of the most massive B-type stars reported to host a magnetic field. We report the detection of a spectroscopic contribution from the C component in high-resolution ESPaDOnS spectra, which is also detected in a Very Large Telescope Interferometer data set. Radial velocity (RV) measurements of the inner binary (designated Aab) yield an orbital period of 14.3027(7) d. The orbit of the third component (designated C) was constrained using both RVs and interferometry. We find C to be on a mildly eccentric 476(1) d orbit. Thanks to spectral disentangling of mean line profiles obtained via least-squares deconvolution, we show that the Zeeman Stokes V signature is clearly associated with C, rather than Aa as previously assumed. The physical parameters of the stars were constrained using both orbital and evolutionary models, yielding M-Aa = 14.9 +/- 0.5 M-circle dot, M-Ab = 3.9 +/- 0.7 M-circle dot, and M-C = 7.8 +/- 0.7 M-circle dot. The rotational period obtained from longitudinal magnetic field (B-z) measurements is P-rot = 1.09468(7)d, consistent with previous results. Modelling of (B-z) indicates a surface dipole magnetic field strength of similar to 8 kG. NU Ori C has a magnetic field strength, rotational velocity, and luminosity similar to many other stars exhibiting magnetospheric Ha emission, and we find marginal evidence of emission at the expected level (similar to 1 per cent of the continuum).

Place, publisher, year, edition, pages
OXFORD UNIV PRESS, 2019
Keywords
binaries: close, stars: early-type, stars: individual: NU Ori, stars: magnetic field, stars: massive
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-381930 (URN)10.1093/mnras/sty2985 (DOI)000462312600076 ()
Funder
Knut and Alice Wallenberg FoundationSwedish Research CouncilSwedish National Space Board
Available from: 2019-04-18 Created: 2019-04-18 Last updated: 2019-04-18Bibliographically approved
Mikulasek, Z., Krticka, J., Paunzen, E., Svanda, M., Hummerich, S., Bernhard, K., . . . Shultz, M. (2018). Differential rotation in magnetic chemically peculiar stars. CONTRIBUTIONS OF THE ASTRONOMICAL OBSERVATORY SKALNATE PLESO, 48(1), 203-207
Open this publication in new window or tab >>Differential rotation in magnetic chemically peculiar stars
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2018 (English)In: CONTRIBUTIONS OF THE ASTRONOMICAL OBSERVATORY SKALNATE PLESO, ISSN 1335-1842, Vol. 48, no 1, p. 203-207Article in journal (Refereed) Published
Abstract [en]

Magnetic chemically peculiar (mCP) stars constitute about 10% of upper-main-sequence stars and are characterized by strong magnetic fields and abnormal photospheric abundances of some chemical elements. Most of them exhibit strictly periodic light, magnetic, radio, and spectral variations that can be fully explained by a rigidly rotating main-sequence star with persistent surface structures and a stable global magnetic field. Long-term observations of the phase curves of these variations enable us to investigate possible surface differential rotation with unprecedented accuracy and reliability. The analysis of the phase curves in the best-observed mCP stars indicates that the location and the contrast of photometric and spectroscopic spots as well as the geometry of the magnetic field remain constant for at least many decades. The strict periodicity of mCP variables supports the concept that the outer layers of upper-main-sequence stars do not rotate differentially. However, there is a small, inhomogeneous group consisting of a few mCP stars whose rotation periods vary on timescales of decades. The period oscillations may reflect real changes in the angular velocity of outer layers of the stars which are anchored by their global magnetic fields. In CU Vir, V901 On, and perhaps BS Cir, the rotational period variation indicates the presence of vertical differential rotation; however, its exact nature has remained elusive until now. The incidence of mCP stars with variable rotational periods is currently investigated using a sample of fifty newly identified Kepler mCP stars.

Place, publisher, year, edition, pages
SLOVAK ACADEMY SCIENCES ASTRONOMICAL INST, 2018
Keywords
stars: chemically peculiar, stars: rotation, stars: individual sigma Ori E, CU Vir, V901 Ori, and BS Cir, space vehicles: Kepler
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-357776 (URN)000432791300028 ()
Available from: 2018-08-22 Created: 2018-08-22 Last updated: 2018-08-22Bibliographically approved
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
Shultz, M., Rivinius, T., Wade, G. A., Alecian, E. & Petit, V. (2018). HD 156324: a tidally locked magnetic triple spectroscopic binary with a disrupted magnetosphere. Monthly notices of the Royal Astronomical Society, 475(1), 839-852
Open this publication in new window or tab >>HD 156324: a tidally locked magnetic triple spectroscopic binary with a disrupted magnetosphere
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2018 (English)In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 475, no 1, p. 839-852Article in journal (Refereed) Published
Abstract [en]

HD 156324 is an SB3 (B2VIB5VIB5V) system in the Sco OB4 association. The He-strong primary possesses both a strong magnetic field and Ha emission believed to originate in its centrifugal magnetosphere. We analyse a large spectroscopic and high-resolution spectropolarimetric data set. The radial velocities (RVs) indicate that the system is composed of two subsystems, which we designate A and B. Period analysis of the RVs of the three components yields orbital periods P-orb = 1.5806(1) d for the Aa and Ab components, and P-orb = 6.67(2) d for the B component, a PGa star. Period analysis of the longitudinal magnetic field (B,) and H alpha equivalent widths, which should both be sensitive to the rotational period Prot of the magnetic Aa component, both yield 1.58 d. Since P-orb = P-rot Aa and Ab must be tidally locked. Consistent with this, the orbit is circularized, and the rotational and orbital inclinations are identical within uncertainty, as are the semimajor axis and the Kepler corotation radius. The star's Ha emission morphology differs markedly from both theoretical and observational expectations in that there is only one, rather than two, emission peaks. We propose that this unusual morphology may be a consequence of modification of the gravitocentrifugal potential by the presence of the close stellar companion. We also obtain upper limits on the magnetic dipole strength B-d for the Ab and B components, respectively, finding B-d < 2.6 and <0.7 kG.

Place, publisher, year, edition, pages
OXFORD UNIV PRESS, 2018
Keywords
binaries: close, stars: early-type, stars: individual: HD 156324, stars: magnetic field, stars: massive
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-354518 (URN)10.1093/mnras/stx3238 (DOI)000427144200066 ()
Available from: 2018-07-18 Created: 2018-07-18 Last updated: 2018-07-18Bibliographically 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
Shultz, M. E., Wade, G. A., Rivinius, T., Neiner, C., Alecian, E., Bohlender, D., . . . Sikora, J. (2018). The magnetic early B-type stars I: magnetometry and rotation. Monthly notices of the Royal Astronomical Society, 475(4), 5144-5178
Open this publication in new window or tab >>The magnetic early B-type stars I: magnetometry and rotation
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2018 (English)In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 475, no 4, p. 5144-5178Article in journal (Refereed) Published
Abstract [en]

The rotational and magnetic properties of many magnetic hot stars are poorly characterized, therefore the Magnetism in Massive Stars and Binarity and Magnetic Interactions in various classes of Stars collaborations have collected extensive high-dispersion spectropo-larimetric data sets of these targets. We present longitudinal magnetic field measurements < B-z > for 52 early B-type stars (B5-B0), with which we attempt to determine their rotational periods P-rot. Supplemented with high-resolution spectroscopy, low-resolution Dominion As-trophysical Observatory circular spectropolarimetry, and archival Hipparcos photometry, we determined P-rot for 10 stars, leaving only five stars for which P-rot could not be determined. Rotational ephemerides for 14 stars were refined via comparison of new to historical magnetic measurements. The distribution of P-rot is very similar to that observed for the cooler Ap/Bp stars. We also measured v sin i and v(mac) for all stars. Comparison to non-magnetic stars shows that v sin i is much lower for magnetic stars, an expected consequence of magnetic braking. We also find evidence that v(mac) is lower for magnetic stars. Least-squares deconvolution profiles extracted using single-element masks revealed widespread, systematic discrepancies in < B-z > between different elements: this effect is apparent only for chemically peculiar stars, suggesting it is a consequence of chemical spots. Sinusoidal fits to H line < B-z > measurements (which should be minimally affected by chemical spots), yielded evidence of surface magnetic fields more complex than simple dipoles in six stars for which this has not previously been reported; however, in all six cases, the second- and third-order amplitudes are small relative to the first-order (dipolar) amplitudes.

Place, publisher, year, edition, pages
Oxford University Press, 2018
Keywords
magnetic fields, stars: chemically peculiar, stars: early-type, stars: magnetic field, stars: massive, stars: rotation
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-351693 (URN)10.1093/mnras/sty103 (DOI)000428835700060 ()
Available from: 2018-06-04 Created: 2018-06-04 Last updated: 2018-06-04Bibliographically approved
Shultz, M., Kochukhov, O., Wade, G. A. & Rivinius, T. (2018). The pulsationally modulated radial crossover signature of the slowly rotating magnetic B-type star xi(1) CMa. Monthly Notices of the Royal Astronomical Society: Letters, 478(1), L39-L43
Open this publication in new window or tab >>The pulsationally modulated radial crossover signature of the slowly rotating magnetic B-type star xi(1) CMa
2018 (English)In: Monthly Notices of the Royal Astronomical Society: Letters, ISSN 1745-3925, Vol. 478, no 1, p. L39-L43Article in journal (Refereed) Published
Abstract [en]

We report the latest set of spectropolarimetric observations of the magnetic beta Cep star xi 1 CMa. The new observations confirm the long-period model of Shultz et al. (2017), who proposed a rotational period of about 30 years and predicted that in 2018 the star should pass through a magnetic null. In perfect agreement with this projection, all longitudinal magnetic field < B-z > measurements are close to 0 G. Remarkably, individual Stokes V profiles all display a crossover signature, which is consistent with < B-z > similar to 0 but is not expected when v sin i similar to 0. The crossover signatures furthermore exhibit pulsationally modulated amplitude and sign variations. We show that these unexpected phenomena can all be explained by a 'radial crossover' effect related to the star's radial pulsations, together with an important deviation of the global field topology from a purely dipolar structure, that we explore via a dipole+ quadrupole configuration as the simplest non-dipolar field.

Place, publisher, year, edition, pages
Oxford University Press (OUP), 2018
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-368684 (URN)10.1093/mnrasl/sly070 (DOI)000450777200008 ()
Funder
Knut and Alice Wallenberg FoundationSwedish Research CouncilSwedish National Space Board
Available from: 2018-12-06 Created: 2018-12-06 Last updated: 2019-01-16Bibliographically approved
Shultz, M. & Wade, G. A. (2017). Confirming the oblique rotator model for the extremely slowly rotating O8f?p star HD 108. Monthly notices of the Royal Astronomical Society, 468(4), 3985-3992
Open this publication in new window or tab >>Confirming the oblique rotator model for the extremely slowly rotating O8f?p star HD 108
2017 (English)In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 468, no 4, p. 3985-3992Article in journal (Refereed) Published
Abstract [en]

The O8f?p star HD 108 is implied to have experienced the most extreme rotational braking of any magnetic, massive star, with a rotational period P-rot of at least 55 yr, but the upper limit on its spin-down time-scale is over twice the age estimated from the Hertzsprung-Russell diagram. HD 108's observed X-ray luminosity is also much higher than predicted by the X-ray Analytical Dynamical Magnetosphere (XADM) model, a unique discrepancy amongst magnetic O-type stars. Previously reported magnetic data cover only a small fraction (similar to 3.5 per cent) of P-rot, and were furthermore acquired when the star was in a photometric and spectroscopic 'low state' at which the longitudinal magnetic field < B-z > was likely at a minimum. We have obtained a new ESPaDOnS magnetic measurement of HD 108, 6 yr after the last reported measurement. The star is returning to a spectroscopic high state, although its emission lines are still below their maximum observed strength, consistent with the proposed 55-yr period. We measured < B-z > = -325 +/- 45 G, twice the strength of the 2007-2009 observations, raising the lower limit of the dipole surface magnetic field strength to B-d >= 1 kG. The simultaneous increase in < B-z > and emission strength is consistent with the oblique rotator model. Extrapolation of the < B-z > maximum via comparison of HD 108's spectroscopic and magnetic data with the similar Of?p star HD 191612 suggests that B-d > 2 kG, yielding t(S,max) < 3 Myr, compatible with the stellar age. These results also yield a better agreement between the observed X-ray luminosity and that predicted by the XADM model.

Keywords
stars: individual: HD108, stars: massive, stars: rotation, stars: winstars: rotationds, outflows
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-327362 (URN)10.1093/mnras/stx759 (DOI)000402819700016 ()
Available from: 2017-08-23 Created: 2017-08-23 Last updated: 2017-08-23Bibliographically approved
Fletcher, C. L., Petit, V., Naze, Y., Wade, G. A., Townsend, R. H., Owocki, S. P., . . . Shultz, M. (2017). Investigating the Magnetospheres of Rapidly Rotating B-type Stars. In: Eldridge, JJ; Bray, JC; McClelland, LAS; Xiao, L (Ed.), Lives And Death-Throes Of Massive Stars: . Paper presented at 329th Symposium of the International-Astronomical-Union (IAU), NOV 28-DEC 02, 2016, Auckland, NEW ZEALAND (pp. 369-372). (S329)
Open this publication in new window or tab >>Investigating the Magnetospheres of Rapidly Rotating B-type Stars
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2017 (English)In: Lives And Death-Throes Of Massive Stars / [ed] Eldridge, JJ; Bray, JC; McClelland, LAS; Xiao, L, 2017, no S329, p. 369-372Conference paper, Published paper (Refereed)
Abstract [en]

Recent spectropolarimetric surveys of bright, hot stars have found that similar to 10% of OB-type stars contain strong (mostly dipolar) surface magnetic fields (similar to kG). The prominent paradigm describing the interaction between the stellar winds and the surface magnetic field is the magnetically confined wind shock (MCWS) model. In this model, the stellar wind plasma is forced to move along the closed field loops of the magnetic field, colliding at the magnetic equator, and creating a shock. As the shocked material cools radiatively it will emit X-rays. Therefore, X-ray spectroscopy is a key tool in detecting and characterizing the hot wind material confined by the magnetic fields of these stars. Some B-type stars are found to have very short rotational periods. The effects of the rapid rotation on the X-ray production within the magnetosphere have yet to be explored in detail. The added centrifugal force due to rapid rotation is predicted to cause faster wind outflows along the field lines, leading to higher shock temperatures and harder X-rays. However, this is not observed in all rapidly rotating magnetic B-type stars. In order to address this from a theoretical point of view, we use the X-ray Analytical Dynamical Magnetosphere (XADM) model, originally developed for slow rotators, with an implementation of new rapid rotational physics. Using X-ray spectroscopy from ESA's XMM-Newton space telescope, we observed 5 rapidly rotating B-types stars to add to the previous list of observations. Comparing the observed X-ray luminosity and hardness ratio to that predicted by the XADM allows us to determine the role the added centrifugal force plays in the magnetospheric X-ray emission of these stars.

Series
IAU Symposium Proceedings Series, ISSN 1743-9213, E-ISSN 1743-9221 ; 12
Keywords
massive stars, magnetic fields, stars, rotation, x-rays
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-377141 (URN)10.1017/S1743921317002812 (DOI)000455603400061 ()978-1-10717-006-3 (ISBN)
Conference
329th Symposium of the International-Astronomical-Union (IAU), NOV 28-DEC 02, 2016, Auckland, NEW ZEALAND
Available from: 2019-02-18 Created: 2019-02-18 Last updated: 2019-02-18Bibliographically approved
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