Multicomponent radiatively driven stellar winds

Krtička, Jiřı́; Kubát, Jiřı́; Groote, D.

doi:10.1051/0004-6361:20065128

Cited by 22 publications

(21 citation statements)

References 60 publications

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“…The spin-down time depends on the stellar parameters, polar magnetic field strength B p , and on the wind parameters, −10 M year −1 . This is a significantly lower value than that derived by Krtička et al (2006) as a result of the use of model atmospheres with metal opacity and CMF line force in the wind models.…”

Section: Rotational Braking Of Bp Starscontrasting

confidence: 54%

“…The wind can be treated as a onecomponent flow at high wind densities, while at low wind densities typical for main-sequence B star winds the effects connected with the multicomponent flow are significant. However, either frictional heating (Springmann & Pauldrach 1992;Krtička et al 2006) or the decoupling of wind components (Owocki & Puls 2002;Votruba et al 2007) typically occur at velocities higher than the critical one, therefore they do not affect the wind mass-loss rate, but may affect the terminal velocity.…”

Section: Model Simplificationsmentioning

confidence: 99%

“…They provide a unique environment in which many astrophysical phenomena can be studied, including the particle collisions that lead to the multicomponent nature of the flow (e.g., Springmann & Pauldrach 1992;Krtička et al 2006), or the line Doppler-heating that influences the wind temperature (Gayley & Owocki 1994). Note, however, that because the latter two effects occur in the outer wind, they typically do not affect the mass-loss rate.…”

Section: Introductionmentioning

confidence: 99%

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Mass loss in main-sequence B stars

Krtička

2014

A&A

116

133

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We calculate radiatively driven wind models of main-sequence B stars and provide the wind mass-loss rates and terminal velocities. The main-sequence mass-loss rate strongly depends on the stellar effective temperature. For the hottest B stars the mass-loss rate amounts to 10 −9 M year −1 , while for the cooler ones the mass-loss rate is lower by more than three orders of magnitude. Mainsequence B stars with solar abundance and effective temperatures lower than about 15 000 K (later than spectral type B5) do not have any homogeneous line-driven wind. We predict the wind mass-loss rates for the solar chemical composition and for the modified abundance of heavier elements to study the winds of chemically peculiar stars. The mass-loss rate may either increase or decrease with increasing abundance, depending on the importance of the induced emerging flux redistribution. Stars with overabundant silicon may have homogeneous winds even below the solar abundance wind limit at 15 000 K. The winds of main-sequence B stars lie below the static limit, that is, a static atmosphere solution is also possible. This points to an important problem regarding the initiation of these winds. We discuss the implications of our models for rotational braking, filling the magnetosphere of Bp stars, and for chemically peculiar stars.

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Section: Rotational Braking Of Bp Starscontrasting

confidence: 54%

Section: Model Simplificationsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Mass loss in main-sequence B stars

Krtička

2014

A&A

116

133

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“…This might explain the discrepancy between the maximum age of HD 37776 derived from the observed period increase and the age of the Orion OB1b association. On the other hand, episodic mass-loss is not expected in the framework of classical radiation-driven wind theory (e.g., Krtička et al 2006). …”

Section: Transient Angular Momentum Lossmentioning

confidence: 99%

The extremely rapid rotational braking of the magnetic helium-strong star HD 37776

Mikulášek

Krtička²,

Henry

et al. 2008

A&A

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Context. Light and spectrum variations of the magnetic chemically peculiar (mCP) stars are explained by the oblique rigid rotator model with a rotation period usually assumed to be stable on a long time scale. A few exceptions, such as CU Vir or 56 Ari, have been reported as displaying an increase in their rotation period. A possible increase in the period of light and spectrum variations has also been suggested from observations of the helium-strong mCP star HD 37776 (V901 Ori). Aims. In this paper we attempt to confirm the possible period change of HD 37776 and discuss a possible origin of this change as a consequence of i) duplicity; ii) precession; iii) evolutionary changes; and iv) continuous/discrete/transient angular momentum loss. Results. We confirm the previously suspected gradual increase in the 1. d 5387 period of HD 37776 and find that it has lengthened by a remarkable 17.7 ± 0.7 s over the past 31 years. We also note that a decrease in the rate of the period change is not excluded by the data. The shapes of light curves in all colours were found to be invariable. Conclusions. After ruling out light-time effects in a binary star, precession of the rotational axis, and evolutionary changes as possible causes for the period change, we interpret this ongoing period increase as a braking of the star's rotation, at least in its surface layers, due to the momentum loss through events or processes in the extended stellar magnetosphere.

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“…(Krtička et al 2006), enough neutral helium atoms in fact seem likely to separate from the polar wind, return to the surface, and accumulate there as helium caps.…”

Section: Introductionmentioning

confidence: 99%

Variations of the high-level Balmer line spectrum of the helium-strong star σ Orionis E

Smith

Bohlender

2007

A&A

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Using the high-level Balmer lines and continuum, we trace the density structure of two magnetospheric disk segments of the prototypical Bp star σ Orionis E (B2p) as these segments occult portions of the star during the rotational cycle. High-resolution spectra of the Balmer lines ≥H9 and Balmer edge were obtained on seven nights in January-February 2007 at an average sampling of 0.01 cycles. We measured equivalent width variations due to the star occultations by two disk segments 0.4 cycles apart and constructed differential spectra of the migrations of the corresponding absorptions across the Balmer line profiles. We first estimated the rotational and magnetic obliquity angles. We then simulated the observed Balmer jump variation using the model atmosphere codes synspec/circus and evaluated the disk geometry and gas thermodynamics. We find that the two occultations are caused by two disk segments. The first of these transits quickly, indicating that the segment resides in a range of distances, perhaps 2.5−6 R * , from the star. The second consists of a more slowly moving segment situated closer to the surface and causing two semi-resolved absorbing maxima. During its transit this segment brushes across the star's "lower" limb. Judging from the line visibility up to H23-H24 during the occultations, both disk segments have mean densities near 10 12 cm −3 and are opaque in the lines and continuum. They have semiheights less than 1 2 R * , and their temperatures are near 10 500 K and 12 000 K, respectively. In all, the disks of Bp stars have a much more complicated geometry than has been anticipated, as evidenced by their (sometimes) non-coplanarity, de-centerness, and from star to star, differences in disk height.

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Multicomponent radiatively driven stellar winds

Cited by 22 publications

References 60 publications

Mass loss in main-sequence B stars

Mass loss in main-sequence B stars

The extremely rapid rotational braking of the magnetic helium-strong star HD 37776

Variations of the high-level Balmer line spectrum of the helium-strong star σ Orionis E

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