A search for linear polarization variability in pole-on Be stars

Hayes, D. P.

doi:10.1086/130726

Cited by 11 publications

(5 citation statements)

References 5 publications

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“…But if this is the case, then 0) Ori and 66 Oph may not be rapidly rotating after all and could instead be viewed equator-on! The large polarization sometimes observed in co Ori (Hayes 1980) seems to be compatible with the latter suggestion.…”

Section: Discussionsupporting

confidence: 80%

“…The visible spectra of 0) Ori and 66 Oph have a history of vari ability (Hubert-Delplace and Hubert 1979). co Ori recently displayed unusual variable polarization (Hayes 1980) to have shown optical flares (Page and Page 1970). Values of vsin i are 160 and 280 km s" 1 , respectively, for u) Ori and 66 Oph (Slettebak 1976); if V e( j -400 km s" 1 , then inclinations of 24° and 44°, respec tively, are implied.…”

Section: Introductionmentioning

confidence: 99%

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Evidence for Mass Loss at Polar Latitudes in ω Ori and 66 Oph

Peters

1982

Symp. - Int. Astron. Union

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IUE observations of the “pole-on” Be stars ω Ori and 66 Oph have revealed the unexpected presence of high velocity (v ≃ −750 km s−1), relatively narrow (Δλ ≃ 1A) absorption components in the resonance lines of C IV, Si III, and Si IV. The C IV features show structure indicative of multiple shells or clouds. Similar high velocity lines were not observed in other pole-on Be stars considered in the program. The nature of these unusual features and the column densities and mass loss rates implied by them are discussed in this paper.

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Section: Discussionsupporting

confidence: 80%

Section: Introductionmentioning

confidence: 99%

Evidence for Mass Loss at Polar Latitudes in ω Ori and 66 Oph

Peters

1982

Symp. - Int. Astron. Union

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“…Underhill (1994) proposed that HD 108 is observed equatorially (i#90°) and possesses an equatorial disc plus bipolar jets. At such an inclination, if the polarimetric variability were attributed to variations in the mass-loss rates of either the disc or the jets, one would expect to see a collinear polarimetric variation in the Q, U plane, as is seen with Be stars (Hayes 1980;Hayes & Guinan 1984;Bjorkman 1991). Such variations are not observed (see Fig.…”

Section: Blob Ejection Modelmentioning

confidence: 91%

“…If so, then the polarimetric variability should be phase-locked (Brown, McLean & Emslie 1978;Rudy & Kemp 1978). If, as according to Underhill (1994), an equatorial disc plus bipolar jets exist, small variations in the mass-loss rates of either geometry will produce collinear polarimetric variations in the normalized Stokes Q, U plane (resulting from geometrical constraints) as observed in Be stars (Hayes 1980;Hayes & Guinan 1984;Bjorkman 1991). If the star is a supergiant or WR star, it is likely to exhibit a random polarimetric variability (Fox & Henrichs 1994).…”

Section: Introductionmentioning

confidence: 99%

The polarimetric nature of HD 108

Fox

Hines

1998

Monthly Notices of the Royal Astronomical Society

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V‐band polarimetric observations of HD 108 were obtained during 1994 August and September. This is the first time that the temporal polarimetric variability of this star has been investigated. Its percentage polarization and position angle vary randomly, and no evidence of its proposed binary nature is detected. The random variability is consistent with that seen for previously observed Wolf–Rayet stars and OB supergiants. Nightly variations do show some systematic behaviour consistent with the blob ejection model of Underhill & Fehey (1984). From the data it is estimated that the mass‐loss rate resulting from blobs is ∼1‐10−7 M⊙ yr−1. The total mass‐loss rate of the star is estimated to be ∼1‐10−5 M⊙ yr−1. The stellar rotation rate is estimated to be Vrot∼400 km s−1 with an inclination of i<20c. The data are also interpreted in terms of perturbations occurring in an equatorial disc plus bipolar jets viewed equatorially (Underhill 1994). It is found that the perturbation mass‐loss rate is about ∼3‐10−7 M⊙ yr−1, giving a total mass‐loss rate for the star of 13‐10−5 M⊙ yr−1. Both models are consistent with HD 108 being an OB supergiant or of the class Ofpe/WR9.

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“…Comprehensive broadband polarimetric surveys had been completed (e.g. Poeckert, Bastien, & Landstreet 1979;Hayes 1980;Poeckert & Marlborough 1976;McLean & Brown 1978). Narrow-band line-scan polarimetry across the Ha and H./3 lines had been done (Poeckert & Marlborough 1977;McLean et al 1979;McLean & Clarke 1979).…”

Section: Application To Be Starsmentioning

confidence: 99%

Polarimetry as a Diagnostic of Circumstellar Envelopes

Bjorkman

2000

International Astronomical Union Colloquium

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Polarimetric observations of stars can provide useful diagnostics of the geometry and physical conditions of the circumstellar envelope. This paper reviews the application of polarimetric techniques to hot stars (with particular emphasis on Be stars) and the status of polarization observations, and discusses some recent developments that improve our ability to make and to interpret such observations. Polarization measurements, bolstered by the increasing availability of new instruments on larger telescopes, continue to improve toward both higher signal-to-noise ratio and higher spectral resolution. Because of this we can begin to address specific questions of the physics of the circumstellar envelopes, since polarization provides a means to separate the effects of the photosphere from those of the envelope. New theoretical and analytic approaches are improving our ability to interpret spectropolarimetric data. We now are able to determine characteristics such as disk opening angle, density, and temperature. Furthermore, polarimetric observations in new wavelength regimes (e.g. ultraviolet and infrared) are opening new avenues to investigate circumstellar disks. The combination of spectropolarimetry with other kinds of data, such as spectroscopy, photometry, and interferometry, shows promise for providing stringent tests for theoretical models of the circumstellar envelopes of Be stars.

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A search for linear polarization variability in pole-on Be stars

Abstract: Five Be stars classified as pole-on were monitored for linear polarization variability. Only one star (

Cited by 11 publications

References 5 publications

Evidence for Mass Loss at Polar Latitudes in ω Ori and 66 Oph

Evidence for Mass Loss at Polar Latitudes in ω Ori and 66 Oph

The polarimetric nature of HD 108

Polarimetry as a Diagnostic of Circumstellar Envelopes

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