The spaces C (X)

Brown, Arlen; Pearcy, Carl

doi:10.1007/978-1-4612-9926-4_18

Cited by 78 publications

(133 citation statements)

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“…Our best-fit P.A. of the major axis is at a right angle to the polarization vector, as expected for the case of electron scattering in an axisymmetric and optically thin disk (Brown & McLean 1977).…”

Section: Best-fit Parameterssupporting

confidence: 80%

The Circumstellar Envelope of Tauri through Optical Interferometry

Tycner¹,

Hajian²,

Armstrong³

et al. 2004

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We present optical interferometric observations of the Be star Tauri obtained using the Navy Prototype Optical Interferometer (NPOI). The multichannel capability of the NPOI allows a high-quality internal calibration of the squared visibilities corresponding to the H emission from the circumstellar environment. The observations suggest a strong departure from circular symmetry and thus are described by an elliptical Gaussian model. We use a nonlinear least-squares fit to the data to obtain the likeliest parameters, and the corresponding uncertainties are determined using a Monte Carlo simulation. We obtain 3:14 AE 0:21 mas for the angular size of the major axis, À62: 3 AE 4: 4 for the position angle, and 0:310 AE 0:072 for the axial ratio. By comparing our results with those already in the literature, we conclude that the model parameters describing the general characteristics of the circumstellar envelope of Tau appear to be stable on timescales of years. We also compare our results with the known parameters describing the binary nature of Tau, and we conclude that the envelope surrounds only the primary component and is well within its Roche lobe.

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Section: Best-fit Parameterssupporting

confidence: 80%

The Circumstellar Envelope of Tauri through Optical Interferometry

Tycner¹,

Hajian²,

Armstrong³

et al. 2004

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“…The degree of polarization is similar to the result of Wolf & Henning (1999), who calculated the polarization for multiple scattering in similar cones. At c < 1, the fluxes and the variations with inclination agree with the analytic solution for single-scattering (e.g., Brown & McLean 1977). At c !…”

Section: Electron Scattering In Conessupporting

confidence: 74%

“…At low t , the scattered light from every scatterer in the torus can be observed. The plane of polarization from a disklike distribution of scatterers, especially when viewed edge-on, is parallel to the polar axis (Brown & McLean 1977). As t gets higher, the light from the conical surface of the torus begins to dominate in the total light, because the light that has entered the torus is absorbed and cannot reach the outer spherical surface.…”

Section: Dust Scattering In Torusmentioning

confidence: 99%

Simultaneous Optical and Near‐Infrared Spectropolarimetry of Type 2 Seyfert Galaxies

Watanabe

Nagata

Sato

et al. 2003

ApJ

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We present optical and near-infrared spectropolarimetry of the nuclei of four type 2 Seyfert galaxies, Mrk 463E, Mrk 1210, NGC 1068, and NGC 4388. The data were obtained simultaneously, covering the wavelength range of 0.46-2.5 lm. We model the polarizations from two dust-scattering components: (1) scattering in dusty regions in ionization cones and (2) scattering in a torus surrounding a type 1 nucleus. The polarizations from electron scattering in the cones and dichroic absorption by aligned dust grains in the torus are also compared with the observations. We confirmed that a combination of electron and dust scattering in the ionization cones is the preferred mechanism for the optical continuum polarization. For the near-infrared, dichroic absorption by aligned grains can explain the continuum polarization of Mrk 463E and Mrk 1210 as well as NGC 1068. Visual optical depths of the order of 10-20 are estimated for dichroic absorption in these nuclei. Dust scattering in the torus, whose grain size distribution is assumed to be the same as in the Galactic diffuse interstellar medium, cannot reproduce the observed spectral slope of the near-infrared polarization and total nuclear flux simultaneously. However, this might only indicate that the grain size distribution in the torus of active galactic nuclei (AGNs) is different, and dust scattering with moderate optical depth and dominated by large grains might provide a reasonable explanation for the near-infrared radiation from AGNs.

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“…6). Indeed, for those stars that have had the position angle of the disk measured, it lies normally to the continuum polarization angle (Quirrenbach et al 1997), as expected for scattering models (e.g., Brown & McLean 1977;Wood et al 1996aWood et al , 1996b. Also, the available axial ratio determinations of the envelopes agree well with the inclination estimates from the emission shape.…”

Section: Geometrical Distributionsupporting

confidence: 63%

Classical Be Stars

Porter

Rivinius²

2003

PUBL ASTRON SOC PAC

599

580

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Recent results for classical Be stars are reviewed and links to general astrophysics are presented. Classical Be stars are B-type stars close to the main sequence that exhibit line emission over the photospheric spectrum. The excess is attributed to a circumstellar gaseous component that is commonly accepted to be in the form of an equatorial disk. Since 1988, when the last such review was published, major progress has been made. The geometry and kinematics of the circumstellar environment can be best explained by a rotationally supported relatively thin disk with very little outflow, consistent with interferometric observations. The presence of shortterm periodic variability is restricted to the earlier type Be stars. This variation for at least some of these objects has been shown to be due to nonradial pulsation. For at least one star, evidence for a magnetic field has been observed. The mechanisms responsible for the production and dynamics of the circumstellar gas are still not constrained. Observations of nonradial pulsation beating phenomena connected to outbursts point toward a relevance of pulsation, but this mechanism cannot be generalized. Either the evidence that Be stars do not form a homogeneous group with respect to disk formation is growing or the short-term periodic variability is less important than previously thought. The statistics of Be stars investigated in open clusters of the Milky Way and the Magellanic Clouds has reopened the question of the evolutionary status of Be stars. The central B star is a fast rotator, although theoretical developments have revived the question of how high rotational rates are, so the commonly quoted mean value of about 70%-80% of the critical velocity may just be a lower limit. Be stars are in a unique position to make contributions to several important branches of stellar physics, e.g., asymmetric mass-loss processes, stellar angular momentum distribution evolution, astroseismology, and magnetic field evolution.

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The spaces C (X)

Cited by 78 publications

References 0 publications

The Circumstellar Envelope of Tauri through Optical Interferometry

The Circumstellar Envelope of Tauri through Optical Interferometry

Simultaneous Optical and Near‐Infrared Spectropolarimetry of Type 2 Seyfert Galaxies

Classical Be Stars

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