THE FIRST DETERMINATION OF THE VISCOSITY PARAMETER IN THE CIRCUMSTELLAR DISK OF A Be STAR

Carciofi, A. C.; Bjorkman, J. E.; Otero, S.; Okazaki, Atsuo T.; Štefl, S.; Rivinius, Thomas; Baade, D.; Haubois, X.

doi:10.1088/2041-8205/744/1/l15

Cited by 95 publications

(124 citation statements)

References 23 publications

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“…Due to the uncertainties on C I and the uncertainties in our model, for now we put a lower limit on α, which must be greater than 0.1. The high α value found in our study is consistent with that inferred for dwarf novae and X-ray outbursts, where discs are fully ionised, which suggest α values ranging from 0.1 to 0.4 (King et al 2007) and also with the value of α = 1 ± 0.2 measured for the fully ionised disc in a Be star (Carciofi et al 2012). Note that the MRI conditions required to be active can involve some complicated non-linear effects (and some non ideal MRI effects), a discussion of which exceeds the scope of this paper (see Kral & Latter 2016, for more details).…”

Section: Discussionsupporting

confidence: 91%

A self-consistent model for the evolution of the gas produced in the debris disc of β Pictoris

Kral¹,

Wyatt²,

Carswell³

et al. 2016

Mon. Not. R. Astron. Soc.

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This paper presents a self-consistent model for the evolution of gas produced in the debris disc of β Pictoris. Our model proposes that atomic carbon and oxygen are created from the photodissociation of CO, which is itself released from volatile-rich bodies in the debris disc due to grain-grain collisions or photodesorption. While the CO lasts less than one orbit, the atomic gas evolves by viscous spreading resulting in an accretion disc inside the parent belt and a decretion disc outside. The temperature, ionisation fraction and population levels of carbon and oxygen are followed with the photodissociation region model Cloudy, which is coupled to a dynamical viscous α model. We present new gas observations of β Pic, of C I observed with APEX and O I observed with Herschel, and show that these along with published C II and CO observations can all be explained with this new model. Our model requires a viscosity α > 0.1, similar to that found in sufficiently ionised discs of other astronomical objects; we propose that the magnetorotational instability is at play in this highly ionised and dilute medium. This new model can be tested from its predictions for high resolution ALMA observations of C I. We also constrain the water content of the planetesimals in β Pic. The scenario proposed here might be at play in all debris discs and this model could be used more generally on all discs with C, O or CO detections.

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Section: Discussionsupporting

confidence: 91%

A self-consistent model for the evolution of the gas produced in the debris disc of β Pictoris

Kral¹,

Wyatt²,

Carswell³

et al. 2016

Mon. Not. R. Astron. Soc.

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“…10. Carciofi et al (2012) obtained similar values for 28 CMa by modelling the decline rate of the V-band excess. Since the values by Waters et al (1987) and Stee (2003) are strongly model dependent, they cannot be taken as strong constraints of the models.…”

Section: Comparison Of the Mass-loss Ratessupporting

confidence: 53%

“…10 shows this upper limit for IR mass-loss rates obtained by Waters et al (1987), and the colour points in this figure show some of their data for which reliable stellar-mass determinations are available in the literature. Stee (2003) also obtained mass-loss rates A25, page 12 of 14 Waters et al (1987), while the black crosses correspond to data from Stee (2003) and the black circle to the data from Carciofi et al (2012) for 28 CMa. The thin dotted curve traces the upper limit for IR mass-loss rates obtained by Waters et al (1987).…”

Section: Comparison Of the Mass-loss Ratesmentioning

confidence: 90%

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Populations of rotating stars

Granada

Ekström

Georgy

et al. 2013

A&A

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Context. Even though it is broadly accepted that single Be stars are rapidly rotating stars surrounded by a flat rotating circumstellar disk, there is still a debate about how fast these stars rotate and also about the mechanisms involved in the angular-momentum and mass input in the disk. Aims. We study the properties of stars that rotate near their critical-rotation rate and investigate the properties of the disks formed by equatorial mass ejections. Methods. We used the most recent Geneva stellar evolutionary tracks for rapidly rotating stars that reach the critical limit and used a simple model for the disk structure. Results. We obtain that for a 9 M star at solar metallicity, the minimum average velocity during the main-sequence (MS) phase to reach the critical velocity is around 330 km s −1 , whereas it would be 390 km s −1 at the metallicity of the Small Magellanic Cloud (SMC). Red giants or supergiants originating from very rapid rotators rotate six times faster and show N/C ratios three times higher than those originating from slowly rotating stars. This difference becomes stronger at lower metallicity. It might therefore be very interesting to study the red giants in clusters that show a large number of Be stars on the MS band. On the basis of our single-star models, we show that the observed Be-star fraction with cluster age is compatible with the existence of a temperature-dependent lower limit in the velocity rate required for a star to become a Be star. The mass, extension, and diffusion time of the disks produced when the star is losing mass at the critical velocity, obtained from simple parametrized expressions, are estimated to be between 9.4 × 10 −12 and 1.4 × 10 −7 M (3 × 10 −6 to 4.7 × 10 −2 times the mass of the Earth), 2000 and 6500 R , and 10 and 30 yr. These values are not too far from those estimated for disks around Be-type stars. At a given metallicity, the mass and the extension of the disk increase with the initial mass and with age on the MS phase. Denser disks are expected in low-metallicity regions.

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“…The VDD scenario in the steady state limit has been successfully tested for several Be stars, using the radiative transfer code HDUST (e.g., Carciofi & Bjorkman 2006;Carciofi et al 2007Carciofi et al , 2009Carciofi et al , 2012. However, there are still several open theoretical questions for the VDD scenario, one of the main ones being the origin and magnitude of the turbulent viscosity.…”

Section: Introductionmentioning

confidence: 99%

An empirical pipeline for determining the viscosity parameter for Be star disks

Rímulo

Carciofi

Rivinius³

et al. 2014

Proc. IAU

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Abstract. Be star phenomenology is strongly associated with their viscous circumstellar disks. Recently, models became available for the temporal evolution of these disks when subject to variable mass ejection rates. In this contribution we will discuss how these dynamical disk models, modeled with the radiative transfer code HDUST, can be used for constraining fundamental disk parameters, such as the α viscosity parameter, and we will report on an ongoing effort to model light curves of a large number of stars.

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THE FIRST DETERMINATION OF THE VISCOSITY PARAMETER IN THE CIRCUMSTELLAR DISK OF A Be STAR

Cited by 95 publications

References 23 publications

A self-consistent model for the evolution of the gas produced in the debris disc of β Pictoris

A self-consistent model for the evolution of the gas produced in the debris disc of β Pictoris

Populations of rotating stars

An empirical pipeline for determining the viscosity parameter for Be star disks

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