Long term disc variability in the Be star<i>o</i>Andromedae

Clark, J. S.; Tarasov, A. E.; Panko, Elena

doi:10.1051/0004-6361:20030248

Cited by 36 publications

(47 citation statements)

References 26 publications

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“…However, as first noted by Struve (1931) rapid (critical) stellar rotation seems to play the key role. Studies on disk formation around the most rapidly rotating stars known, i.e., the classical Be stars, revealed that their disks are most probably driven by viscosity (see, e.g., Porter 1999;Okazaki 2001;Jones et al 2008), resulting in quasi-Keplerian rotating disks with a slow (few km s −1 ) equatorial outflow component, in agreement with observations (Clark et al 2003). The star S 65 also seems to be rotating (close to) critical.…”

Section: Possible Disk Formation Mechanismsupporting

confidence: 79%

Neutral material around the B[e] supergiant star LHA 115-S 65

Kraus¹,

Fernandes²,

Araújo³

2010

A&A

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Context. B[e] supergiants are surrounded by large amounts of hydrogen neutral material, traced by the emission in the optical [Oi] lines. This neutral material is most plausibly located within their dense, cool circumstellar disks, which are formed from the (probably non-spherically symmetric) wind material released by the star. Neither the formation mechanism nor the resulting structure and internal kinematics of these disks (or disk-like outflows) are well known. However, rapid rotation, lifting the material from the equatorial surface region, seems to play a fundamental role. Aims. The B[e] supergiant LHA 115-S 65 (in short: S 65) in the Small Magellanic Cloud is one of the two most rapidly rotating B[e] stars known. Its almost edge-on orientation allows a detailed kinematical study of its optically thin forbidden emission lines. With a focus on the rather strong [Oi] lines, we intend to test the two plausible disk scenarios: the outflowing and the Keplerian rotating disk. Methods. Based on high-and low-resolution optical spectra, we investigate the density and temperature structure in those disk regions that are traced by the [Oi] emission to constrain the disk sizes and mass fluxes needed to explain the observed [Oi] line luminosities. In addition, we compute the emerging line profiles expected for either an outflowing disk or a Keplerian rotating disk, which can directly be compared to the observed profiles. Results. Both disk scenarios deliver reasonably good fits to the line luminosities and profiles of the [Oi] lines. Nevertheless, the Keplerian disk model seems to be the more realistic one, because it also agrees with the kinematics derived from the large number of additional lines in the spectrum. As additional support for the presence of a high-density, gaseous disk, the spectrum shows two very intense and clearly double-peaked [Caii] lines. We discuss a possible disk-formation mechanism, and similarities between S 65 and the group of Luminous Blue Variables.

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Section: Possible Disk Formation Mechanismsupporting

confidence: 79%

Neutral material around the B[e] supergiant star LHA 115-S 65

Kraus¹,

Fernandes²,

Araújo³

2010

A&A

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“…The B6e star o And has also experienced shell and diskloss episodes, as discussed in (Clark et al 2003). Their Figs.…”

Section: Discussionmentioning

confidence: 97%

The discovery of a shell-like event in the O-type star HD 120678

Gamen

Arias

Barbá

et al. 2012

A&A

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Aims. We report the detection of a shell-like event in the Oe-type star HD 120678. Methods. HD 120678 has been intensively observed as part of a high-resolution spectroscopic monitoring program of southern Galactic O stars and Wolf-Rayet stars of the nitrogen sequence.Results. An optical spectrogram of HD 120678 obtained in June 2008 shows strong H and He i absorption lines instead of the double-peaked emission profiles observed both previously and subsequently, as well as a variety of previously undetected absorption features, mainly of O ii, Si iii and Fe iii. Photometric data reveal that the development of the absorption spectrum coincided with a remarkable dip in the V-band lightcurve. The "shell phase" of HD 120678 did not persist for very long: the V magnitude recovered its previous average value in fewer than 120 days, whereas H and He emission lines became detectable one year later. Similar spectral variations have been observed in a few Be stars, and they are usually interpreted as changes in the circumstellar disk.

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“…Arguably the most dramatic type of variability observed is the aperiodic "Be to normal B to Be" transition whereby classical Be stars dissipate (i.e., lose) their disks, and will often begin to regenerate a new disk after a period of relative quiescence (see, e.g., Underhill & Doazan 1982 and references therein). While several individual stars have been observed to experience this transition one or more times (Underhill & Doazan 1982;Doazan et al 1983;Clark et al 2003;Vinicius et al 2006), it is not known whether there is a characteristic timescale for disk loss and regeneration that would suggest a singular disk formation mechanism or whether each event is unique. Although their sample size is small, recent monitoring of eight open clusters by McSwain et al (2009) has revealed a surprising 12 new transient Be stars out of a sample of 296 stars monitored, suggesting that disk-loss/renewal episodes may be a prevalent phenomenon.…”

Section: Introductionmentioning

confidence: 99%

DISK-LOSS AND DISK-RENEWAL PHASES IN CLASSICAL Be STARS. I. ANALYSIS OF LONG-TERM SPECTROPOLARIMETRIC DATA

Wisniewski

Draper

Bjorkman

et al. 2010

ApJ

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Classical Be stars are known to occasionally transition from having a gaseous circumstellar disk ("Be phase") to a state in which all observational evidence for the presence of these disks disappears ("normal B-star phase"). We present one of the most comprehensive spectropolarimetric views to date of such a transition for two Be stars, π Aquarii and 60 Cygni.The disk-loss episode of 60 Cyg was characterized by a generally monotonic decrease in emission strength over a timescale of ∼1000 days from the maximum V-band polarization to the minimum Hα equivalent width, consistent with the viscous timescale of the disk, assuming α ∼0.14. π Aqr's disk loss was episodic in nature and occurred over a timescale of ∼2440 days. An observed time lag between the behavior of the polarization and Hα in both stars indicates the disk clearing proceeded in an "inside-out" manner. We determine the position angle of the intrinsic polarization to be 166.• 7 ± 0.• 1 for π Aqr and 107.• 7 ± 0.• 4 for 60 Cyg, and model the wavelength dependence of the observed polarization during the quiescent diskless phase of each star to determine the interstellar polarization along the line of sight. Minor outbursts observed during the quiescent phase of each star shared similar lifetimes as those previously reported for μ Cen, suggesting that the outbursts represent the injection and subsequent viscous dissipation of individual blobs of material into the inner circumstellar environments of these stars. We also observe deviations from the mean intrinsic polarization position angle during polarization outbursts in each star, indicating deviations from axisymmetry. We propose that these deviations might be indicative of the injection (and subsequent circularization) of new blobs into the inner disk, either in the plane of the bulk of the disk material or in a slightly inclined (non-coplanar) orbit.

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Long term disc variability in the Be staroAndromedae

Cited by 36 publications

References 26 publications

Neutral material around the B[e] supergiant star LHA 115-S 65

Neutral material around the B[e] supergiant star LHA 115-S 65

The discovery of a shell-like event in the O-type star HD 120678

DISK-LOSS AND DISK-RENEWAL PHASES IN CLASSICAL Be STARS. I. ANALYSIS OF LONG-TERM SPECTROPOLARIMETRIC DATA

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