Cyclic variability of the circumstellar disk of the Be star<i>ζ</i>Tauri

Carciofi, A. C.; Okazaki, Atsuo T.; Bouquin, J.-B. Le; Štefl, S.; Rivinius, Thomas; Baade, D.; Bjorkman, J. E.; Hummel, C. A.

doi:10.1051/0004-6361/200810962

Cited by 118 publications

(187 citation statements)

References 39 publications

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“…It is known that companions can influence the circumstellar disks of Be stars in several ways: affecting the global disk oscillations (Oktariani & Okazaki 2009), truncating the outer disk (Carciofi et al 2009), and even extracting material from the central star in eccentric orbits (Miroshnichenko et al 2001;Kervella et al 2008). The latter authors found that the orbital period of the close companion of Achernar (HD 10144) appears similar to the observed pseudo-periodicity of the Be phenomenon, indicating that an interaction between the components at periastron could be triggering the Be episodes.…”

Section: Discussionmentioning

confidence: 99%

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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Section: Discussionmentioning

confidence: 99%

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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“…Major outbursts might temporarily lead to such a situation but the cyclic variability would probably require them, too, to be cyclic. A perturbation that propagates in a spiral-like pattern has a physical foundation in global m = 1 disk oscillations, which will be developed into a fully self-consistent model in Paper II (Carciofi et al 2009). …”

Section: Discussionmentioning

confidence: 99%

Cyclic variability of the circumstellar disk of the Be starζ Tauri

Štefl¹,

Rivinius²,

Carciofi

et al. 2009

A&A

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Context. Emission lines formed in decretion disks of Be stars often undergo long-term cyclic variations, especially in the violet-to-red (V/R) ratio of their primary components. The underlying structural and dynamical variations of the disks are only partly understood. From observations of the bright Be-shell star ζ Tau, the possibly broadest and longest data set illustrating the prototype of this behaviour was compiled from our own and archival observations. It comprises optical and infrared spectra, broad-band polarimetry, and interferometric observations. Aims. The dense, long-time monitoring permits a better separation of repetitive and ephemeral variations. The broad wavelength coverage includes lines formed under different physical conditions, i.e. different locations in the disk, so that the dynamics can be probed throughout much of the disk. Polarimetry and interferometry constrain the spatial structure. All together, the objective is a better understand the dynamics and life cycle of decretion disks. Methods. Standard methods of data acquisition, reduction, and analysis were applied. Results. From 3 V/R cycles between 1997 and 2008, a mean cycle length in Hα of 1400-1430 days was derived. After each minimum in V/R, the shell absorption weakens and splits into two components, leading to 3 emission peaks. This phase may make the strongest contribution to the variability in cycle length. There is no obvious connection between the V/R cycle and the 133-day orbital period of the not otherwise detected companion. V/R curves of different lines are shifted in phase. Lines formed on average closer to the central star are ahead of the others. The shell absorption lines fall into 2 categories differing in line width, ionization/excitation potential, and variability of the equivalent width. They seem to form in separate regions of the disk, probably crossing the line of sight at different times. The interferometry has resolved the continuum and the line emission in Brγ and HeI 2.06. The phasing of the Brγ emission shows that the photocenter of the line-emitting region lies within the plane of the disk but is offset from the continuum source. The plane of the disk is constant throughout the observed V/R cycles. The observations lay the foundation for the fully self-consistent, one-armed, disk-oscillation model developed in Paper II.

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“…Electron scattering modified by pre-or postscattering absorption by hydrogen atoms in the disk produces the characteristic wavelength-dependent polarization signature of Be stars (Wood et al 1996a(Wood et al , 1996b. Modeling such data yields information about the density in the inner region of these disks (Wood et al 1997;Carciofi et al 2009) and has been used, along with interferometric observations, to confirm that the disks are geometrically thin (Quirrenbach et al 1997). …”

Section: Disk-loss and Disk-renewal Phases In Classical Be Stars I mentioning

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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Cyclic variability of the circumstellar disk of the Be starζTauri

Cited by 118 publications

References 39 publications

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

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

Cyclic variability of the circumstellar disk of the Be starζ Tauri

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

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