Rotational Velocity Versus Mass Loss in Be Stars

Doazan, V.; Franco, Maximilien; Stalio, R.; Thomas, R. N.

doi:10.1007/978-94-009-8565-0_53

Cited by 29 publications

(37 citation statements)

References 2 publications

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“…The long-term variations of this star, including changes in the Balmer emission lines, the visual apparent magnitude, and the V/R ratio, have been described by several authors (Doazan et al 1983, and references therein). The occurrence of three phases -Be, Be-shell and B quasi-normal -has been reported.…”

Section: Discussionmentioning

confidence: 74%

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: 74%

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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“…Finally, some authors recently returned to the model of flattened ellipsoids or spheroidal envelopes (Moujtahid et al 1999) similar to those proposed earlier by Doazan & Thomas (1982). Although a low level of intrinsic polarization of Be stars is considered as an indication that the envelope must be strongly flattened, other geometries can produce the same level of polarization (see Wood et al 1996aWood et al , 1996b.…”

Section: Introductionmentioning

confidence: 83%

Statistical analysis of intrinsic polarization, IR excess and projected rotational velocity distributions of classical Be stars

Yudin

2001

A&A

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Abstract. We present the results of statistical analyses of a sample of 627 Be stars. The parameters of intrinsic polarization (p * ), projected rotational velocity (v sin i), and near IR excesses have been investigated. The values of p * have been estimated for a much larger and more representative sample of Be stars (≈490 objects) than previously. We have confirmed that most Be stars of early spectral type have statistically larger values of polarization and IR excesses in comparison with the late spectral type stars. It is found that the distributions of p * diverge considerably for the different spectral subgroups. In contrast to late spectral types (B5-B9.5), the distribution of p * for B0-B2 stars does not peak at the value p * = 0%. Statistically significant differences in the mean projected rotational velocities (v sin i) are found for different spectral subgroups of Be stars in the sense that late spectral type stars (V luminosity class) generally rotate faster than early types, in agreement with previously published results. This behaviour is, however, not obvious for the III-IV luminosity class stars. Nevertheless, the calculated values of the ratio vt/vc of the true rotational velocity, vt, to the critical velocity for break-up, vc, is larger for late spectral type stars of all luminosity classes. Thus, late spectral type stars appear to rotate closer to their break-up rotational velocity. The distribution of near IR excesses for early spectral subgroups is bi-modal, the position of the second peak displaying a maximum value E(V − L) ≈ 1 . m 3 for O-B1.5 stars, decreasing to E(V − L) ≈ 0 . m 8 for intermediate spectral types (B3-B5). It is shown that bi-modality disappears for late spectral types (B6-B9.5). No correlations were found between p * and near IR excesses and between E(V − L) and v sin i for the different subgroups of Be stars. In contrast to near IR excesses, a relation between p * and far IR excesses at 12 µm is clearly seen. A clear relation between p * and v sin i (as well as between p * and v sin i/vc) is found by the fact that plots of these parameters are bounded by a "triangular" distribution of p * : v sin i, with a decrease of p * towards very small and very large v sin i (and v sin i/vc) values. The latter behaviour can be understood in the context of a larger oblateness of circumstellar disks for the stars with a rapid rotation. From the analysis of correlations between different observational parameters we conclude that circumstellar envelopes for the majority of Be stars are optically thin disks with the range of the half-opening angle of 10• < Θ < 40• .

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“…Poretti (1982) classified the star as γ Cas type: however, in γ Cas (B0 IVe) the light variations are less frequent (occuring typically over decades) and of a much larger amplitude (i.e. more than one magnitude, see Doazan et al 1983) than those observed in Figs. 1 and 2.…”

Section: Discussionmentioning

confidence: 99%

Monitoring the activity of the Be star OT Geminorum

Ferro

Sareyan

Avila

et al. 1998

Astron. Astrophys. Suppl. Ser.

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Abstract. Observations obtained in 1995-1996 of the Be star OT Geminorum are reported and show that in october 1995 the star reached a very active phase with large variations around a bright plateau, a phase of activity we have also distinguished in previous observations dating from 1960.The time scales involved are discussed and suggest that the violent variations of the activity propagate very quickly on the whole surface of the star or on a huge portion of it. No likely pulsation periods were found.The assumption that the detected activity is due to the effects of an hypothetical companion leads to conclude that such companion could not be detected by the present interferometric techniques.

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Rotational Velocity Versus Mass Loss in Be Stars

Cited by 29 publications

References 2 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

Statistical analysis of intrinsic polarization, IR excess and projected rotational velocity distributions of classical Be stars

Monitoring the activity of the Be star OT Geminorum

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