Constraints on the surface magnetic fields of hot stars with winds

Maheswaran, M.; Cassinelli, J. P.

doi:10.1086/171049

Cited by 23 publications

(18 citation statements)

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“…This model distribution starts as roughly corotational, i.e., v ðdÞ / d, and transitions to a v decreasing with d. This distribution is clearly not truly Keplerian disk v ðdÞ / 1= ffiffiffi d p . However, the typical v is comparable with v K and exists over only a rather narrow range of d, unless the field is very strong, which is unlikely on theoretical grounds (Maheswaran & Cassinelli 1988; cf. Figure 9).…”

Section: Discussionmentioning

confidence: 99%

“…Arbitrarily large could centrifuge and contain a disk of arbitrary radial extent. However, depends on the surface field for which there are bounds as described by Maheswaran & Cassinelli (1988, so there are, in fact, upper bounds to as well.…”

Section: The Description Of the Angular Velocity V ðXþ In The Diskmentioning

confidence: 99%

“…Table 1 also includes representative values of B 0; th for S 0 ¼ 0:5, 0.7, 0.9. Figure 9 shows the comparison the minimal field from equation (43) along with the bounds on stellar magnetic fields that were derived by Maheswaran & Cassinelli (1988. The latter bounds were derived from considerations of envelope circulation currents and maximal contributions of field pressure to hydrostatic support.…”

Section: Hot Main-sequence Stars and The Possibilities For Disk Produmentioning

confidence: 99%

“…Figure 11 shows the dependence of the Fig. 9.-Limits derived for the maximal and minimal field strengths for Be stars vs. S 0 derived from photospheric constraints of Maheswaran & Cassinelli (1992). The solid line shows the minimal B 0 as a function of S 0 such that a disk can be magnetically torqued; for these calculations we use the stellar parameters from Table 1, b ¼ 3, and ¼ 1.…”

Section: Radial Extentmentioning

confidence: 99%

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A Magnetically Torqued Disk Model for Be Stars

Cassinelli

Brown

Maheswaran

et al. 2002

ApJ

105

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Despite extensive study, the mechanisms by which Be star disks acquire high densities and angular momentum while displaying variability on many timescales are still far from clear. In this paper, we discuss how magnetic torquing may help explain disk formation with the observed quasi-Keplerian (as opposed to expanding) velocity structure and their variability. We focus on the effects of the rapid rotation of Be stars, considering the regime where centrifugal forces provide the dominant radial support of the disk material. Using a kinematic description of the angular velocity, v ðrÞ, in the disk and a parametric model of an aligned field with a strength BðrÞ, we develop analytic expressions for the disk properties that allow us to estimate the stellar surface field strength necessary to create such a disk for a range of stars on the main sequence. The fields required to form a disk are compared with the bounds previously derived from photospheric limiting conditions. The model explains why disks are most common for main-sequence stars at about spectral class B2 V. The earlier type stars with very fast and high-density winds would require unacceptably strong surface fields (>10 3 G) to form torqued disks, while the late B stars (with their low mass-loss rates) tend to form disks that produce only small fluxes in the dominant Be diagnostics. For stars at B2 V the average surface field required is about 300 G. The predicted disks provide an intrinsic polarization and a flux at H comparable to observations. The radial extent of our dense quasi-Keplerian disks is compatible with typical estimates. We also discuss whether the effect on field containment of the time-dependent accumulation of matter in the flux tubes/disk can help explain some of the observed variability of Be star disks.

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Section: Discussionmentioning

confidence: 99%

Section: The Description Of the Angular Velocity V ðXþ In The Diskmentioning

confidence: 99%

Section: Hot Main-sequence Stars and The Possibilities For Disk Produmentioning

confidence: 99%

Section: Radial Extentmentioning

confidence: 99%

See 2 more Smart Citations

A Magnetically Torqued Disk Model for Be Stars

Cassinelli

Brown

Maheswaran

et al. 2002

ApJ

105

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“…There are no direct measurements of the stellar magnetic fields, although they are usually thought to be of the order of a few Gauss (e.g. Maheswaran & Cassinelli 1992). We have adopted values of 2 and 1 G for the primary and the secondary, respectively.…”

Section: The Stellar System Cyg Ob2 Nomentioning

confidence: 99%

Can the gamma-ray source 3EG J2033+4118 be produced by the stellar system Cygnus OB2 No. 5?

Benaglia

Romero

Stevens

et al. 2001

A&A

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Abstract. We discuss the possibility that the stellar system Cyg OB2 No. 5 can be a gamma-ray source in the light of recent EGRET and radio data. This system is formed by an O7 Ia + Ofpe/WN9 contact binary. A third star, probably a B0 V star also associated with the system, is located at ∼1700 AU from the primary. We estimate the expected gamma-ray luminosity from the colliding winds region, the terminal shock of the wind, and the unstable zone at the base of the wind, and conclude that, under very reasonable assumptions, Cyg OB2 No. 5 can generate about a half of the gamma-ray flux detected from the positionally coincident source 3EG J2033+4118. We suggest, then, that other O stars belonging to the association, also placed within the 95% probability EGRET location contour, could contribute to the observed gamma-ray flux.

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