“Stellar Prominences” on OB starsto explain wind-line variability

Henrichs, H.F.; Sudnik, N.

doi:10.1017/s1743921314002282

Cited by 5 publications

(9 citation statements)

References 18 publications

(17 reference statements)

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“…Although some quasicyclic behaviour with a typical timescale near 2 days, interpreted as half the rotation period, was found at some epochs (Henrichs & Sudnik 2014), the variations do not seem to be strictly (mono)periodic, but are reminiscent of the epoch-dependent variability found in other Oef stars (Rauw et al 2003; 2 . Henrichs & Sudnik (2014) accordingly suggest that the variations might arise from the presence of several transient short-lived magnetic loops corotating with the star. The localized magnetic fields responsible for these loops could take their origin in sub-surface convective layers of the star.…”

Section: Optical Variabilitymentioning

confidence: 86%

“…The variability of the star's emission lines has been subsequently studied by a number of authors (Lacy 1977;Leep & Conti 1979;Ebbets 1982;Grady et al 1983;McCandliss 1988;Henrichs et al 1988;Henrichs 1991;Kaper et al 1997Kaper et al , 1999Markova et al 2005). Although some quasicyclic behaviour with a typical timescale near 2 days, interpreted as half the rotation period, was found at some epochs (Henrichs & Sudnik 2014), the variations do not seem to be strictly (mono)periodic, but are reminiscent of the epoch-dependent variability found in other Oef stars (Rauw et al 2003; 2 . Henrichs & Sudnik (2014) accordingly suggest that the variations might arise from the presence of several transient short-lived magnetic loops corotating with the star.…”

Section: Optical Variabilitymentioning

confidence: 99%

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Simultaneous X-ray and optical spectroscopy of the Oef supergiantλCephei

Rauw

Hervé

Nazé

et al. 2015

A&A

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Context. Probing the structures of stellar winds is of prime importance for the understanding of massive stars. Based on their optical spectral morphology and variability, it has been suggested that the stars in the Oef class feature large-scale structures in their wind. Aims. High-resolution X-ray spectroscopy and time-series of X-ray observations of presumably single O-type stars can help us understand the physics of their stellar winds. Methods. We have collected XMM-Newton observations and coordinated optical spectroscopy of the O6 Ief star λ Cep to study its X-ray and optical variability and to analyse its high-resolution X-ray spectrum. We investigate the line profile variability of the He ii λ 4686 and Hα emission lines in our time series of optical spectra, including a search for periodicities. We further discuss the variability of the broadband X-ray flux and analyse the high-resolution spectrum of λ Cep using line-by-line fits as well as a code designed to fit the full high-resolution X-ray spectrum consistently.Results. During our observing campaign, the He ii λ 4686 line varies on a timescale of ∼18 h. On the contrary, the Hα line profile displays a modulation on a timescale of 4.1 days which is likely the rotation period of the star. The X-ray flux varies on timescales of days and could in fact be modulated by the same 4.1-day period as Hα, although both variations are shifted in phase. The highresolution X-ray spectrum reveals broad and skewed emission lines as expected for the X-ray emission from a distribution of windembedded shocks. Most of the X-ray emission arises within less than 2 R * above the photosphere. Conclusions. The properties of the X-ray emission of λ Cep generally agree with the expectations of the wind-embedded shock model. There is mounting evidence for the existence of large-scale structures that modulate the Hα line and about 10% of the X-ray emission of λ Cep.

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Section: Optical Variabilitymentioning

confidence: 86%

Section: Optical Variabilitymentioning

confidence: 99%

Simultaneous X-ray and optical spectroscopy of the Oef supergiantλCephei

Rauw

Hervé

Nazé

et al. 2015

A&A

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“…We calculated the spectra according to Henrichs & Sudnik (2014) model where the line profile variability induced by the stellar prominences represented as a spheres touching the stellar surface. The prominence will give extra absorption or emission in the line profile depending on its location in the line of sight.…”

Section: Nrp and Rotational Modulationmentioning

confidence: 99%

Smoothed Temporal Variance Spectrum: weak line profile variations and NRP diagnostics

Холтыгин

Sudnik

2016

Mon. Not. R. Astron. Soc.

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We describe the version of the Temporal Variance Spectrum (TVS, Fullerton, Gies & Bolton 1996) method with pre-smoothed line profile (smoothed Temporal Variance Spectrum, smTVS). This method introduced by Kholtygin et al. (2003) can be used to detect the ultra weak variations of the line profile even for very noisy stellar spectra. We also describe how to estimate the mode of the non-radial pulsations (NRP) using the TVS and smTVS with different time spans. The influence of the rotational modulation of the line profile on the TVS is considered. The analysis of the contribution of NRP and rotational modulation in the global TVS is studied.

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“…We therefore consider the most simplified model to represent a "stellar prominence" by a sphere corotating and touching the surface. The model properties are described by Henrichs & Sudnik (2014). Essential in our procedure is that quotient spectra are fitted, such that the overal shape of the profile cancels out.…”

Section: Optical Wind-line Variability In the O6i(n)fp Star λ Cepmentioning

confidence: 99%

“…This variability is not periodic, but cyclic (like sunspots) with often a dominant quasi period which scales with the estimated rotation period (days to weeks), or perhaps an integer fraction thereof, see for instance references in Henrichs & Sudnik (2014), also for the remainder of this contribution. The cause or trigger is unknown.…”

Section: Introductionmentioning

confidence: 99%

Multiple, short-lived “stellar prominences” on O stars: the supergiant λ Cephei

Henrichs¹,

Sudnik²

2014

Proc. IAU

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Abstract. Many OB stars show unexplained cyclical variability in their winds and in many optical lines, which are formed at the base of the wind. For these stars no dipolar magnetic fields have been detected. We propose that these cyclical variations are caused by the presence of multiple, transient, short-lived, corotating magnetic loops, which we call "stellar prominences". We present a simplified model representing these prominences as corotating spherical blobs and fit the rapid variability in the Heii λ4686 line of the O supergiant λ Cep for time-resolved spectra obtained in 1989. Our conclusions are: (1) From model fits we find that the life time of the prominences varies, and is between 2-7 h. (2) The adopted inclination angle is 68• with a rotation period of ≈ 4.1 d (but not well constrained). (3) The contribution of non-radial pulsations is negligible (4) Similar behavior is observed in at least 4 other O stars. We propose that prominences are a common phenomenon among O stars.

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“Stellar Prominences” on OB starsto explain wind-line variability

Cited by 5 publications

References 18 publications

Simultaneous X-ray and optical spectroscopy of the Oef supergiantλCephei

Simultaneous X-ray and optical spectroscopy of the Oef supergiantλCephei

Smoothed Temporal Variance Spectrum: weak line profile variations and NRP diagnostics

Multiple, short-lived “stellar prominences” on O stars: the supergiant λ Cephei

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