Magnetorotational instability in decretion disks of critically rotating stars and the outer structure of Be and Be/X-ray disks

Krtička, Jiřı́; Kurfürst, Petr; Krtičková, Iva

doi:10.1051/0004-6361/201424867

Cited by 12 publications

(11 citation statements)

References 54 publications

(69 reference statements)

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“…Except for a few cases, most of the observed spectra require a very large extra velocity often exceeding 200 km s −1 . Such a velocity amounts to more than one third of the Keplerian velocity at the stellar surface (690 km s −1 ) and exceeds the turbulent velocities predicted by the models of the magnetorotational instability of Krtička et al (2015), which are rather of the order of the local sound speed. Part of these large values could stem from the fact that our model does not account for non-coherent electron scattering that could enhance the wings of the emission lines.…”

Section: Hα Line Profile Fittingmentioning

confidence: 72%

Intriguing X-ray and optical variations of the γ Cassiopeiae analog HD 45314

Rauw

Nazé

Smith

et al. 2018

A&A

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Context. A growing number of Be and Oe stars, named the γ Cas stars, are known for their unusually hard and intense X-ray emission. This emission could either trace accretion by a compact companion or magnetic interaction between the star and its decretion disk. Aims. To test these scenarios, we carried out a detailed optical monitoring of HD 45314, the hottest member of the class of γ Cas stars, along with dedicated X-ray observations on specific dates. Methods. High-resolution optical spectra were taken to monitor the emission lines formed in the disk, while X-ray spectroscopy was obtained at epochs when the optical spectrum of the Oe star was displaying peculiar properties. Results. Over the last four years, HD 45314 has entered a phase of spectacular variations. The optical emission lines have undergone important morphology and intensity changes including transitions between single-and multiple-peaked emission lines as well as shell events, and phases of (partial) disk dissipation. Photometric variations are found to be anti-correlated with the equivalent width of the Hα emission. Whilst the star preserved its hard and bright X-ray emission during the shell phase, the X-ray spectrum during the phase of (partial) disk dissipation was significantly softer and weaker. Conclusions. The observed behaviour of HD 45314 suggests a direct association between the level of X-ray emission and the amount of material simultaneously present in the Oe disk as expected in the magnetic star-disk interaction scenario.

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Section: Hα Line Profile Fittingmentioning

confidence: 72%

Intriguing X-ray and optical variations of the γ Cassiopeiae analog HD 45314

Rauw

Nazé

Smith

et al. 2018

A&A

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“…Some theories propose that the disk is fed by the wind. We used the list of Be/X-ray binaries given in Krtička et al (2015) to test whether the radiatively driven wind can survive the strong X-rays source in Be/X-ray binaries. In many Be/X-ray binaries the compact source is located at large distance from the Be star, and, consequently, it can not disrupt its wind.…”

Section: Be/x-ray Binariesmentioning

confidence: 99%

X-ray irradiation of the winds in binaries with massive components

Krtička

Kubát

Krtičková

2015

A&A

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Context. Binaries with hot massive components are strong X-ray sources. Besides the intrinsic X-ray emission of individual binary members originating in their winds, X-ray emission stems from the accretion on the compact companion or from wind collision. Since hot star winds are driven by the light absorption in the lines of heavier elements, wind acceleration is sensitive to the ionization state. Therefore, the over-ionization induced by external X-ray source strongly influences the winds of individual components. Aims. We studied the effect of external X-ray irradiation on hot star winds. Methods. We used our kinetic equilibrium (NLTE) wind models to estimate the influence of external X-ray ionization for different X-ray luminosities and source distances. The models are calculated for parameters typical of O stars.Results. The influence of X-rays is given by the X-ray luminosity, by the optical depth between a given point and the X-ray source, and by a distance to the X-ray source. Therefore, the results can be interpreted in the diagrams of X-ray luminosity vs. the optical depth parameter. X-rays are negligible in binaries with low X-ray luminosities or at large distances from the X-ray source. The influence of X-rays is stronger for higher X-ray luminosities and in closer proximity of the X-ray source. There is a forbidden area with high X-ray luminosities and low optical depth parameters, where the X-ray ionization leads to wind inhibition. There is excellent agreement between the positions of observed stars in these diagrams and our predictions. All wind-powered high-mass X-ray binary primaries lie outside the forbidden area. Many of them lie close to the border of the forbidden area, indicating that their X-ray luminosities are self-regulated. We discuss the implications of our work for other binary types. Conclusions. X-rays have a strong effect on the winds in binaries with hot components. The magnitude of the influence of X-rays can be estimated from the position of a star in the diagram of X-ray luminosity vs. the optical depth parameter.

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“…Curé 2004;Curé et al 2005) or the magneto-rotational instability mechanism (e.g. Krtička et al 2015;Kurfürst et al 2014). Alternative scenarios with single stars include mass-loss events triggered by non-radial pulsations and/or other instabilities, or the presence of objects (e.g.…”

mentioning

confidence: 99%

Resolving the kinematics of the discs around Galactic B[e] supergiants

Maravelias

Kraus

Cidale

et al. 2018

Monthly Notices of the Royal Astronomical Society

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B[e] Supergiants are luminous evolved massive stars. The mass-loss during this phase creates a complex circumstellar environment with atomic, molecular, and dusty regions usually found in rings or disk-like structures. For a better comprehension of the mechanisms behind the formation of these rings, detailed knowledge about their structure and dynamics is essential. To address that, we obtained high-resolution optical and near-infrared spectra for 8 selected Galactic B[e] Supergiants, for which CO emission has been detected. Assuming Keplerian rotation for the disk, we combine the kinematics obtained from the CO bands in the near-IR with those obtained by fitting the forbidden emission [O i] λ5577, [O i] λλ6300,6363, and [Ca ii] λλ7291,7323 lines in the optical to probe the disk structure. We find that the emission originates from multiple ring structures around all B[e] Supergiants, with each one of them displaying a unique combination of rings regardless of whether the object is part of a binary system. The confirmed binaries display spectroscopic variations of their line intensities and profiles as well as photometric variability, whereas the ring structures around the single stars are stable.

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Magnetorotational instability in decretion disks of critically rotating stars and the outer structure of Be and Be/X-ray disks

Cited by 12 publications

References 54 publications

Intriguing X-ray and optical variations of the γ Cassiopeiae analog HD 45314

Intriguing X-ray and optical variations of the γ Cassiopeiae analog HD 45314

X-ray irradiation of the winds in binaries with massive components

Resolving the kinematics of the discs around Galactic B[e] supergiants

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