Radial dependence of line profile variability in seven O9–B0.5 stars

Martins, F.; Marcolino, W. L. F.; Hillier, D. J.; Donati, J. F.; Bouret, J. C.

doi:10.1051/0004-6361/201423882

Cited by 35 publications

(41 citation statements)

References 40 publications

(81 reference statements)

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“…phenomenon, which they interpreted as NRP. This is supported by Martins et al (2015) who showed that of all optical hydrogen and helium lines, this line is formed deepest in the photosphere, although modeled for a somewhat cooler star than λ Cep. Our 2012 dataset is undersampled to confirm any conclusion regarding NRP.…”

Section: Effect Of Non-radial Pulsationsmentioning

confidence: 60%

Multiple short-lived stellar prominences on O stars: The O6.5I(n)fp starλCephei

Sudnik

Henrichs

2016

A&A

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Context. Most O-type stars and many B stars show unexplained cyclical variability in their spectral lines, i.e., modulation on the rotational timescale, but not strictly periodic. The variability occurs in the so-called discrete absorption components (DACs) that accelerate through the UV-wind line profiles and also in many optical lines. For such OB stars no dipolar magnetic fields have been detected with upper limits of ∼300 G. Aims. We investigate whether multiple magnetic loops on the surface rather than non-radial pulsations or a dipolar magnetic field can explain the observed cyclical UV and optical spectral line variability. Methods. We present time-resolved, high-resolution optical spectroscopy of the O6.5I(n)fp star λ Cephei. We apply a simplified phenomenological model in which multiple spherical blobs attached to the surface represent magnetic-loop structures, which we call stellar prominences, by analogy with solar prominences. We compare the calculated line profiles as a function of rotational phase, adopting a rotation period of 4.1 d, with observed relative changes in subsequent quotient spectra. Results. We identify many periodicities in spectral lines, almost none of which is stable over timescales from months to years. We show that the relative changes in various optical absorption and emission lines are often very similar. Our proposed model applied to the He ii λ4686 line can typically be fitted with 2−5 equatorial blobs with lifetimes between ∼1 and 24 h.Conclusions. Given the irregular timescales involved, we propose that the azimuthal distribution of DACs correspond to the locations of stellar prominences attached to the surface. This could explain the observed variability of optical and UV lines, and put constraints on the strength and lifetime of these structures, which can be compared with recent theoretical predictions, in which bright magnetic surface spots are formed by the action of the subsurface convection zone.

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Section: Effect Of Non-radial Pulsationsmentioning

confidence: 60%

Multiple short-lived stellar prominences on O stars: The O6.5I(n)fp starλCephei

Sudnik

Henrichs

2016

A&A

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“…The behaviour of the λ4542 line can likely be understood as due to the depth of formation and the relative contribution of the magnetosphere to the line profile. Martins et al (2014) constrained the line formation region of various lines in spectra of nonmagnetic O stars, and investigated the variability as a function of depth. They demonstrate that the Balmer lines are formed further out in the wind compared to some weak He i or high ionization He ii or C iv lines.…”

Section: Discussionmentioning

confidence: 99%

Rotation, spectral variability, magnetic geometry and magnetosphere of the Of?p star CPD −28° 2561★

Wade

Barbá

Grunhut

et al. 2015

Monthly Notices of the Royal Astronomical Society

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We report magnetic and spectroscopic observations and modeling of the Of?p star CPD −28• 2561. Using more than 75 new spectra, we have measured the equivalent width variations and examined the dynamic spectra of photospheric and wind-sensitive spectral lines. A period search results in an unambiguous 73.41 d variability period. High resolution spectropolarimetric data analyzed using Least-Squares Deconvolution yield a Zeeman signature detected in the mean Stokes V profile corresponding to phase 0.5 of the spectral ephemeris. Interpreting the 73.41 d period as the stellar rotational period, we have phased the equivalent widths and inferred longitudinal field measurements. The phased magnetic data exhibit a weak sinusoidal variation, with maximum of about 565 G at phase 0.5, and a minimum of about -335 G at phase 0.0, with extrema approximately in phase with the (double-wave) Hα equivalent width variation. Modeling of the Hα equivalent width variation assuming a quasi-3D magnetospheric model produces a unique solution for the ambiguous couplet of inclination and magnetic obliquity angles: (i, β) or (β, i) = (35• , 90 • ). Adopting either geometry, the longitudinal field variation yields a dipole polar intensity B d = 2.6 ± 0.9 kG, consistent with that obtained from direct modelling of the Stokes V profiles. We derive a wind magnetic confinement parameter η * ≃ 100, leading to an Alfvén radius R A ≃ 3 − 5 R * , and a Kepler radius R K ≃ 20 R * . This supports a physical scenario in which the Hα emission and other line variability have their origin in an oblique, co-rotating 'dynamical magnetosphere' structure resulting from a magnetically channeled wind. Nevertheless, the details of the formation of spectral lines and their variability within this framework remain generally poorly understood.

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“…HD 112244 is an emission-line object and has strong stellar wind. Martins et al (2015) have shown that rapid and apparently irregular variability of the wind line profiles is characteristic of the OB supergiants. This is also true for HD 112244 as illustrated in Fig.…”

Section: Hd 112244mentioning

confidence: 99%

Physical properties of seven binary and higher-order multiple OB systems

Mayer

Harmanec

Chini

et al. 2017

A&A

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Analyses of multi-epoch, high-resolution (R ∼ 50000) optical spectra of seven early-type systems provided various important new insights with respect to their multiplicity. For HD 93146 A, which was hitherto assumed to be SB1, lines of a secondary component could be discerned. HD 123056 turns out to be a multiple system consisting of a high-mass component A (≈ O8.5) displaying a broad He ii 5411 Å feature with variable radial velocity, and of an inner pair B (≈ B0) with double He i lines. The binary HD 164816 was revisited and some of its system parameters were improved. In particular, we determined its systemic velocity to be −7 km s −1 , which coincides with the radial velocity of the cluster NGC 6530. This fact, together with its distance, suggests the cluster membership of HD 164816. The OB system HD 318015 (V1082 Sco) belongs to the rare class of eclipsing binaries with a supergiant primary (B0.5/0.7). Our combined orbital and light-curve analysis suggests that the secondary resembles an O9.5 III star. Our results for a limited sample corroborate the findings that many O stars are actually massive multiple systems.

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Radial dependence of line profile variability in seven O9–B0.5 stars

Cited by 35 publications

References 40 publications

Multiple short-lived stellar prominences on O stars: The O6.5I(n)fp starλCephei

Multiple short-lived stellar prominences on O stars: The O6.5I(n)fp starλCephei

Rotation, spectral variability, magnetic geometry and magnetosphere of the Of?p star CPD −28° 2561★

Physical properties of seven binary and higher-order multiple OB systems

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