Constraints on the Geometry of Circumstellar Envelopes: Optical Interferometric and Spectropolarimetric Observations of Seven Be Stars

Quirrenbach, A.; Bjorkman, K. S.; Bjorkman, J. E.; Hummel, C. A.; Buscher, David F.; Armstrong, J. T.; Mozurkewich, David; Elias, N. M.; Babler, B.

doi:10.1086/303854

Cited by 271 publications

(345 citation statements)

References 45 publications

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“…This is similar to the K -band size of 1.8 mas computed by Gies et al (2007) and smaller than the 3.1 -4.5 mas FWHM measured in Hα by Quirrenbach et al (1997) and Tycner et al (2004). We find that the star contributes on average about 55% of the light in the H-band.…”

Section: Abstract Techniques: Interferometric Circumstellar Mattersupporting

confidence: 83%

Multi-epoch interferometric observations of the Be star ζ Tau

et al. 2010

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Abstract. We present interferometric observations of the Be star ζ Tau obtained using the MIRC beam combiner at the CHARA Array during four epochs in [2007][2008][2009]. Fitting a geometric model to the data reveals a nearly edge-on disk with a FWHM of ∼ 1.8 milli-arcsec in the H-band. The non-zero closure phases indicate an asymmetry in the brightness distribution. Interestingly, when combining our results with previously published interferometric observations of ζ Tau, we find a correlation between the position angle of the disk and the spectroscopic V /R ratio, suggesting that the tilt of the disk might be precessing. This work is part of a multiyear monitoring campaign to investigate the development and outward motion of asymmetric structures in the disks of Be stars. Keywords. techniques: interferometric, circumstellar matter, stars: emission-line, BeThe bright Be star ζ Tau is an ideal target for optical/infrared interferometry. We used the MIRC beam combiner at the CHARA Array to measure interferometrically the size and orientation of the disk of ζ Tau in the H-band over four epochs in [2007][2008][2009]. The visibilities provide information on the size, orientation, and inclination of the disk. The non-zero closure phases indicate an asymmetry in the brightness distribution.We fit a two component geometric model to the MIRC data obtained for ζ Tau. The model is composed of a uniform disk with an angular diameter 0.40 mas (R = 5.5 R ) to fit the central star and an elliptical Gaussian surface brightness distribution to model the circumstellar disk. To account for the asymmetry, we modulated the elliptical Gaussian disk by a sinusoid as a function of azimuth. This creates a skewed disk model where the sinusoid causes the brightness distribution to peak on one side of the disk and places a depression in the brightness on the other side. The models are shown in Figure 1.Over the four epochs, the FWHM of the major axis of the disk ranges between 1.6 -2.1 mas in the H-band. This is similar to the K -band size of 1.8 mas computed by Gies et al. (2007) and smaller than the 3.1 -4.5 mas FWHM measured in Hα by Quirrenbach et al. (1997) and Tycner et al. (2004). We find that the star contributes on average about 55% of the light in the H-band. In comparison, the star contributes 41% of the flux in the K -band (Gies et al. 2007). These ratios are consistent with near-IR excess fluxes observed by Touhami et al. (2010).Combining our results with previous interferometric observations, we find that the position angle of the major axis of the ζ Tau disk varies as a function of the spectroscopic V /R phase (see Fig. 2). The disks of Be stars may develop a global, one-armed spiral instability. The oscillation mode forms a spiral density enhancement that precesses prograde with the disk rotation with a cycle time of a few years. We suspect that the 424 at https://www.cambridge.org/core/terms. https://doi

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Section: Abstract Techniques: Interferometric Circumstellar Mattersupporting

confidence: 83%

Multi-epoch interferometric observations of the Be star ζ Tau

et al. 2010

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“…Interferometric, direct imaging as well as polarimetric observations show that the gas must be located in a highly flattened circumstellar disk (e.g. Quirrenbach et al 1997). Be stars show no circumstellar dust (with only a few exceptions) and also lack molecular line emission and forbidden lines.…”

Section: The Sample Of Stars and The Iso Spectramentioning

confidence: 99%

Hydrogen infrared recombination lines as a diagnostic tool for the geometry of the circumstellar material of hot stars

Lenorzer

Koter

Waters

2002

A&A

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Abstract.We have analysed the infrared hydrogen recombination lines of a sample of well studied hot massive stars observed with the Infrared Space Observatory. Our sample contains stars from several classes of objects, whose circumstellar environment is believed to be dominated by an ionized stellar wind (the Luminous Blue Variables) or by a dense disk-like geometry (Be stars and B[e] stars). We show that hydrogen infrared recombination lines can be used as a diagnostic tool to constrain the geometry of the ionized circumstellar material. The line strengths are sensitive to the density of the emitting gas. High densities result in optically thick lines for which line strengths are only dependent on the emitting surface. Low density gas produces optically thin lines which may be characterized by Menzel case B recombination. The ISO observations show that stellar winds are dominated by optically thin H i recombination lines, while disks are dominated by optically thick lines. Disks and winds are well separated in a diagnostic diagram using the Hu(14-6)/Brα and the Hu(14-6)/Pfγ line flux ratios. This diagnostic tool is useful to constrain the nature of hot star environments in case they are highly obscured, for instance while they are still embedded in their natal molecular cloud.

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“…Evidence has been accumulated to confirm Struve's (1931) original suggestion that the Be envelopes are rotationally flattened disks. An ultimate proof of this statement came from spectro-interferometric and spectropolarimetric observations of several Be stars which allowed a partial spatial resolution of their envelopes -see Quirrenbach et al (1993Quirrenbach et al ( , 1997.…”

Section: The Be Phenomenonmentioning

confidence: 99%

On the role of duplicity in the Be phenomenon

Harmanec

Bisikalo

Boyarchuk

et al. 2002

A&A

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Abstract. This paper begins a new series of studies devoted to a critical re-examination of the role of duplicity for the Be phenomenon and for the variability patterns observed for many Be stars. Based on both dynamical and energy considerations and a numerical gas-dynamical modelling, a new hypothesis of the formation of Be envelopes in binaries, via an outflow from a rapidly rotating B star in a detached binary, is outlined. It is shown that such an outflow is facilitated by the presence of a companion to the B star and leads to the formation of an envelope but not to any significant mass exchange between the binary components.

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Constraints on the Geometry of Circumstellar Envelopes: Optical Interferometric and Spectropolarimetric Observations of Seven Be Stars

Cited by 271 publications

References 45 publications

Multi-epoch interferometric observations of the Be star ζ Tau

Multi-epoch interferometric observations of the Be star ζ Tau

Hydrogen infrared recombination lines as a diagnostic tool for the geometry of the circumstellar material of hot stars

On the role of duplicity in the Be phenomenon

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