On X-ray pulsations in<i>β</i>Cephei-type variables

Oskinova, L. M.; Todt, H.; Huenemoerder, David P.; Hubrig, S.; Ignace, Richard; Hamann, Wolf-Rainer; Balona, L. A.

doi:10.1051/0004-6361/201525908

Cited by 11 publications

(11 citation statements)

References 38 publications

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“…Pulsations and magnetic fields might be also related to Xray variability that has been discovered in some stars (Oskinova et al 2014;Nazé et al 2014). However, only weak evidence for X-ray variability was found in β Cen (Cohen et al 1997;Raassen et al 2005;Oskinova et al 2015). In general, however, the presence of a magnetic field can be regarded as another complication in the interpretation of the pulsation spectrum of β Cen.…”

Section: Magnetic Field Of the Secondarymentioning

confidence: 99%

“…At the main sequence stage of evolution and shortly beyond, massive stars may become pulsationally unstable owing to the κ mechanism which drives both pressure (p) and gravity (g) modes Pamyatnykh 1999). This presents an opportunity to probe their interiors by means of asteroseismology, and to decipher the internal rotation profile, the extent of core overshooting, and to test the input physics, especially the stellar opacities.…”

Section: Introductionmentioning

confidence: 99%

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Massive pulsating stars observed by BRITE-Constellation

Pigulski

Cugier

Popowicz

et al. 2016

A&A

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Context. Asteroseismology of massive pulsating stars of β Cep and SPB types can help us to uncover the internal structure of massive stars and understand certain physical phenomena that are taking place in their interiors. We study β Centauri (Agena), a triple system with two massive fast-rotating early B-type components which show p-and g-mode pulsations; the system's secondary is also known to have a measurable magnetic field. Aims. This paper aims to precisely determine the masses and detect pulsation modes in the two massive components of β Cen with BRITE-Constellation photometry. In addition, seismic models for the components are considered and the effects of fast rotation are discussed. This is done to test the limitations of seismic modeling for this very difficult case. Methods. A simultaneous fit of visual and spectroscopic orbits is used to self-consistently derive the orbital parameters, and subsequently the masses, of the components. Time-series analysis of BRITE-Constellation data is used to detect pulsation modes and derive their frequencies, amplitudes, phases, and rates of frequency change. Theoretically-predicted frequencies are calculated for the appropriate evolutionary models and their stability is checked. The effects of rotational splitting and coupling are also presented. Results. The derived masses of the two massive components are equal to 12.02 ± 0.13 and 10.58 ± 0.18 M . The parameters of the wider, A-B system, presently approaching periastron passage, are constrained. Analysis of the combined blue-and red-filter BRITEConstellation photometric data of the system revealed the presence of 19 periodic terms, of which eight are likely g modes, nine are p modes, and the remaining two are combination terms. It cannot be excluded that one or two low-frequency terms are rotational frequencies. It is possible that both components of β Cen are β Cep/SPB hybrids. An attempt to use the apparent changes of frequency to distinguish which modes originate in which component did not succeed, but there is potential for using this method when more BRITE data become available. Conclusions. Agena seems to be one of very few rapidly rotating massive objects with rich p-and g-mode spectra, and precisely known masses. It can therefore be used to gain a better understanding of the excitation of pulsations in relatively rapidly rotating stars and their seismic modeling. Lacking proper mode identification, the pulsation frequencies found in β Cen cannot yet be used to constrain the internal structure of the components, but it may be possible to achieve this in the future with the use of spectroscopy and spectropolarimetry. In particular, these kinds of data can be used for mode identification since they provide new radial velocities. In consequence, they may help to improve the orbital solution, derive more precise masses, magnetic field strength and geometry, inclination angles, and reveal rotation periods. They may also help to assign pulsation frequencies to components. Finally, the case studied here ...

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Section: Magnetic Field Of the Secondarymentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Massive pulsating stars observed by BRITE-Constellation

Pigulski

Cugier

Popowicz

et al. 2016

A&A

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“…The star's X-ray emission spectrum is very hard, and the brightest amongst all magnetic β Cep stars, as demonstrated with Einstein (Cassinelli et al 1994), ROSAT (Cassinelli et al 1994), and XMM-Newton (Oskinova et al 2011). The star's X-ray emission has recently been shown to be modulated with the pulsation period (Oskinova et al 2014), a so-far unique discovery amongst massive magnetic pulsators (Favata et al 2009;Oskinova et al 2015) 1 . Various wind-sensitive ultraviolet lines show strong emission (Schnerr et al 2008), which is typical for magnetic stars.…”

Section: Introductionmentioning

confidence: 99%

The pulsating magnetosphere of the extremely slowly rotating magnetic β Cep star ξ1 CMa

Shultz

Wade

Rivinius

et al. 2017

Monthly Notices of the Royal Astronomical Society

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ξ1 CMa is a monoperiodically pulsating, magnetic β Cep star with magnetospheric X-ray emission which, uniquely amongst magnetic stars, is clearly modulated with the star's pulsation period. The rotational period P rot has yet to be identified, with multiple competing claims in the literature. We present an analysis of a large ESPaDOnS dataset with a 9-year baseline. The longitudinal magnetic field B z shows a significant annual variation, suggesting that P rot is at least on the order of decades. The possibility that the star's Hα emission originates around a classical Be companion star is explored and rejected based upon VLTI AMBER and PIONIER interferometry, indicating that the emission must instead originate in the star's magnetosphere and should therefore also be modulated with P rot . Period analysis of Hα EWs measured from ESPaDOnS and CORALIE spectra indicates P rot > 30 yr. All evidence thus supports that ξ 1 CMa is a very slowly rotating magnetic star hosting a dynamical magnetosphere. Hα also shows evidence for modulation with the pulsation period, a phenomenon which we show cannot be explained by variability of the underlying photospheric line profile, i.e. it may reflect changes in the quantity and distribution of magnetically confined plasma in the circumstellar environment. In comparison to other magnetic stars with similar stellar properties, ξ 1 CMa is by far the most slowly rotating magnetic B-type star, is the only slowly rotating B-type star with a magnetosphere detectable in Hα (and thus, the coolest star with an optically detectable dynamical magnetosphere), and is the only known early-type magnetic star with Hα emission modulated by both pulsation and rotation.

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“…A connection between the pulsations at the level of the photosphere and the X‐ray emission generated in the stellar wind suggests that the pulsations trigger part of the wind instabilities. In a subsequent study, Oskinova et al () investigated archival XMM‐Newton and Chandra data of three other β Cep stars (κ Sco, β Cru, α Vir). While weak indications of X‐ray variability were found in β Cru, no statistically significant evidence of pulsations was obtained.…”

Section: What We Have Learned So Farmentioning

confidence: 99%

Perspectives for observing hot massive stars with XMM‐Newton in the years 2017–2027

Rauw

2017

Astron Nachr

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XMM-Newton has deeply changed our picture of X-ray emission of hot, massive stars. High-resolution X-ray spectroscopy as well as monitoring of these objects helped us gain a deeper insight into the physics of single massive stars with or without magnetic fields, as well as of massive binary systems, where the stellar winds of both stars interact. These observations also revealed a number of previously unexpected features that challenge our understanding of the dynamics of the stellar winds of massive stars. I briefly summarize the results obtained over the past 15 years and highlight the perspectives for the next decade. It is anticipated that coordinated (X-ray and optical or UV) monitoring and time-critical observations of either single or binary massive stars will become the most important topics in this field over the coming years. Synergies with existing or forthcoming X-ray observatories (NuStar, Swift, eROSITA) will also play a major role and will further enhance the importance of XMM-Newton in our quest for understanding the physics of hot, massive stars.

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On X-ray pulsations inβCephei-type variables

Cited by 11 publications

References 38 publications

Massive pulsating stars observed by BRITE-Constellation

Massive pulsating stars observed by BRITE-Constellation

The pulsating magnetosphere of the extremely slowly rotating magnetic β Cep star ξ1 CMa

Perspectives for observing hot massive stars with XMM‐Newton in the years 2017–2027

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