DYNAMICAL EVOLUTION OF VISCOUS DISKS AROUND Be STARS. I. PHOTOMETRY

Haubois, X.; Carciofi, A. C.; Rivinius, Thomas; Okazaki, Atsuo T.; Bjorkman, J. E.

doi:10.1088/0004-637x/756/2/156

Cited by 112 publications

(248 citation statements)

References 42 publications

(48 reference statements)

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“…Rivinius et al 2001). Recently, the spreading out of such discs is also attempted to be understood in terms of viscous evolution (Haubois et al 2012), similarly to what we propose here for the FRMS discs. The formation of stars as opposed to planets in circumstellar discs might seem unusual.…”

Section: Top-heavy Imfsupporting

confidence: 62%

“…This process is analogous to the equatorial mass loss in Be-type stars (e.g. Rivinius et al 2001;Townsend et al 2004;Haubois et al 2012). In FRMS, the total amount of mass lost by this process is rather high, and it is hardly plausible that the ejected material may immediately leave the vicinity of the star: to lift the material out of the gravitational potential of the parent star, an energy supply at a rate of GMṀ/(2R dd ) is required if the decretion disc is first established at a characteristic radius R dd after being ejected.…”

Section: Equatorial Mass Ejectionsmentioning

confidence: 85%

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Superbubble dynamics in globular cluster infancy

Krause

Charbonnel

Decressin

et al. 2013

A&A

138

155

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Context. The self-enrichment scenario for globular clusters (GC) requires large amounts of residual gas after the initial formation of the first stellar generation. Recently, we found that supernovae may not be able to expel that gas, as required to explain their presentday gas-free state, and suggested that a sudden accretion onto the dark remnants at a stage when type II supernovae have ceased may plausibly lead to fast gas expulsion. Aims. Here, we explore the consequences of these results for the self-enrichment scenario via fast-rotating massive stars (FRMS). Methods. We analysed the interaction of FRMS with the intra-cluster medium (ICM), in particular where, when, and how the second generation of stars may form. From the results, we developed a timeline of the first ≈40 Myr of GC evolution. Results. Our previous results imply three phases during which the ICM is in a fundamentally different state, namely the wind bubble phase (lasting 3.5 to 8.8 Myr), the supernova phase (lasting 26.2 to 31.5 Myr), and the dark remnant accretion phase (lasting 0.1 to 4 Myr): (i) Quickly after the first-generation massive stars have formed, stellar wind bubbles compress the ICM into thin filaments. No stars may form in the normal way during this phase because of the high Lyman-Werner flux density. If the first-generation massive stars have equatorial ejections however, as we proposed in the FRMS scenario, accretion may resume in the shadow of the equatorial ejecta. The second-generation stars may then form due to gravitational instability in these disc, which are fed by both the FRMS ejecta and pristine gas. (ii) In the supernova phase the ICM develops strong turbulence, with characteristic velocities below the escape velocity. The gas does not accrete either onto the stars or onto the dark remnants in this phase because of the high gas velocities. The strong mass loss associated with the transformation of the FRMS into dark remnants then leads to the removal of the secondgeneration stars from the immediate vicinity of the dark remnants. (iii) When the supernovae have ceased, turbulence quickly decays, and the gas can once more accrete, now onto the dark remnants. As discussed previously, this may release sufficient energy to unbind the gas, and may happen fast enough so that a large fraction of less tightly bound first-generation stars are lost. Conclusions. Studying the FRMS scenario for the self-enrichment of GCs in detail reveals the important role of the physics of the ICM for our understanding of the formation and early evolution of GCs. Depending on the level of mass segregation, this sets constraints on the orbital properties of the stars, in particular high orbital eccentricities, which likely has implications on the GC formation scenario.

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Section: Top-heavy Imfsupporting

confidence: 62%

Section: Equatorial Mass Ejectionsmentioning

confidence: 85%

Superbubble dynamics in globular cluster infancy

Krause

Charbonnel

Decressin

et al. 2013

A&A

138

155

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“…For isothermal Be disks fed at a (nearly) constant rate from the central star, it can be demonstrated that the radial density is a power law with n = 3.5. However, disks either subjected to varying mass feeding rates, or undergoing build-up or dissipation phases, will have much more complex density slopes (Haubois et al 2012), which are here simulated by allowing n to be a free parameter.…”

Section: The Disk Brightness Profilementioning

confidence: 99%

The pseudo-photosphere model for the continuum emission of gaseous discs

Vieira¹,

Carciofi²,

Bjorkman³

2015

Mon. Not. R. Astron. Soc.

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The continuum emission of viscous decretion disks around Be stars is investigated. The results obtained from non-LTE radiative transfer models show two regimes in the disk surface brightness profile: an inner optically thick region, which behaves as a pseudo-photosphere with a wavelength-dependent size, and an optically thin tenuous outer part, which contributes with about a third of the total flux. The isophotal shape of the surface brightness is well described by elliptical contours with an axial ratio b/a = cos i for inclinations i < 75• . Based on these properties, a semi-analytical model was developed to describe the continuum emission of gaseous disks. It provides fluxes and spectral slopes at the infrared within an accuracy of 10% and 5%, respectively, when compared to the numerical results. The model indicates that the infrared spectral slope is mainly determined by both the density radial slope and the disk flaring exponent, being practically independent of disk inclination and base density. As a first application, the density structure of 15 Be stars was investigated, based on the infrared flux excess, and the results compared to previous determinations in the literature. Our results indicate that the decretion rates are in the range of 10 −12 to 10 −9 M ⊙ yr −1 , which is at least two orders of magnitude smaller than the previous outflowing disk model predictions.

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“…The original source of this classification is unclear, but since that the star shows several Be-star typical outbursts (see Fig. 1 vs. Haubois et al 2012, for a theoretical model how such outbursts produce the observed light curve) there is no strong reason to doubt the classification.…”

Section: Hd 186567 (Kic 11971405)mentioning

confidence: 99%

Short-term variability and mass loss in Be stars

Rivinius

Baade

Carciofi

2016

A&A

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Context. Classical Be stars have been established as pulsating stars. Space-based photometric monitoring missions contributed significantly to that result. However, whether Be stars are just rapidly rotating SPB or β Cep stars, or whether they have to be understood differently, remains debated in the view of their highly complex power spectra. Aims. Kepler data of three known Be stars are re-visited to establish their pulsational nature and assess the properties of additional, non-pulsational variations. The three program stars turned out to be one inactive Be star, one active, continuously outbursting Be star, and one Be star transiting from a non-outbursting into an outbursting phase, thus forming an excellent sample to distill properties of Be stars in the various phases of their life-cycle. Methods. The Kepler data was first cleaned from any long-term variability with Lomb-Scargle based pre-whitening. Then a LombScargle analysis of the remaining short-term variations was compared to a wavelet analysis of the cleaned data. This offers a new view on the variability, as it enables us to see the temporal evolution of the variability and phase relations between supposed beating phenomena, which are typically not visualized in a Lomb-Scargle analysis. Results. The short-term photometric variability of Be stars must be disentangled into a stellar and a circumstellar part. The stellar part is on the whole not different from what is seen in non-Be stars. However, some of the observed phenomena might be to be due to resonant mode coupling, a mechanism not typically considered for B-type stars. Short-term circumstellar variability comes in the form of either a group of relatively well-defined, short-lived frequencies during outbursts, which are called Štefl frequencies, and broad bumps in the power spectra, indicating aperiodic variability on a time scale similar to typical low-order g-mode pulsation frequencies, rather than true periodicity. Conclusions. From a stellar pulsation perspective, Be stars are rapidly rotating SPB stars, that is they pulsate in low order g-modes, even if the rapid rotation can project the observed frequencies into the traditional high-order p-mode regime above about 4 c/d. However, when a circumstellar disk is present, Be star power spectra are complicated by both cyclic, or periodic, and aperiodic circumstellar phenomena, possibly even dominating the power spectrum.

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DYNAMICAL EVOLUTION OF VISCOUS DISKS AROUND Be STARS. I. PHOTOMETRY

Cited by 112 publications

References 42 publications

Superbubble dynamics in globular cluster infancy

Superbubble dynamics in globular cluster infancy

The pseudo-photosphere model for the continuum emission of gaseous discs

Short-term variability and mass loss in Be stars

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