On the Determination of the Rotational Oblateness of Achernar

Abstract

The recent interferometric study of Achernar, leading to the conclusion that its geometrical oblateness cannot be explained in the Roche approximation, has stirred substantial interest in the community, in view of its potential impact in many fields of stellar astrophysics. It is the purpose of this paper to reinterpret the interferometric observations with a fast rotating, gravity darkened central star surrounded by a small equatorial disk, whose presence is consistent with contemporaneous spectroscopic data. We find that we can only fit the available data assuming a critically rotating central star. We identified two different disk models that simultaneously fit the spectroscopic, polarimetric, and interferometric observational constraints: a tenuous disk in hydrostatic equilibrium (i.e., with small scaleheight) and a smaller, scaleheight enhanced disk. We believe that these relatively small disks correspond to the transition region between the photosphere and the circumstellar environment, and that they are probably perturbed by some photospheric mechanism. The study of this interface between photosphere and circumstellar disk for near-critical rotators is crucial to our understanding of the Be phenomenon, and the mass and angular momentum loss of stars in general. This work shows that it is nowadays possible to directly study this transition region from simultaneous multi-technique observations.

arXiv comment4 pages, 2 figures. Accepted to ApJ Letters

References in corpus (7)

• Effects of gravitational darkening on the determination of fundamental parameters in fast rotating B-type stars
• The spinning-top Be star Achernar from VLTI-VINCI
• NLTE Monte Carlo Radiative Transfer: I. The Thermal Properties of Keplerian Disks around Classical Be Stars
• First direct detection of a Keplerian rotating disk around the Be star $\alpha$ Arae using the VLTI/AMBER instrument
• Properties of the $\delta$ Scorpii Circumstellar Disk from Continuum Modeling
• Achernar: Rapid Polarization Variability as Evidence of Photospheric and Circumstellar Activity
• The environment of the fast rotating star Achernar - High-resolution thermal infrared imaging with VISIR in BURST mode

Cited by in corpus (26)

• Classical Be Stars: Rapidly Rotating B Stars with Viscous Keplerian Decretion Disks
• The rotation rates of massive stars: the role of binary interaction through tides, mass transfer and mergers
• Interferometric Observations of Rapidly Rotating Stars
• Populations of rotating stars. - I. Models from 1.7 to 15 Msun at Z = 0.014, 0.006, and 0.002 with Ω/Ωcrit between 0 and 1
• The life cycles of Be viscous decretion discs: fundamental disc parameters of 54 SMC Be stars
• Cyclic Variability of the Circumstellar Disc of the Be Star $\zeta$ Tau. II. Testing the 2D Global Disc Oscillation Model
• Effects of anisotropic winds on massive stars evolution
• The pseudo-photosphere model for the continuum emission of gaseous discs
• Effects of Uniform and Differential Rotation on Stellar Pulsations
• The close-in companion of the fast rotating Be star Achernar
• Critical angular velocity and anisotropic mass loss of rotating stars with radiation-driven winds
• Towards Understanding The B[e] Phenomenon: IV. Modeling of IRAS 00470+6429
• Internal Structure and Apsidal Motions of Polytropic Stars in Close Binaries
• An investigation of the photometric variability of confirmed and candidate Galactic Be stars using ASAS-3 data
• Differential rotation in rapidly rotating early-type stars. I. Motivations for combined spectroscopic and interferometric studies
• Theoretical p Mode Oscillation Frequencies for the Rapidly Rotating Delta Scuti Star Alpha Ophiuchi
• The Thermal Structure of Gravitationally-Darkened Classical Be Star Disks
• Matching the Spectral Energy Distribution and p Mode Oscillation Frequencies of the Rapidly Rotating Delta Scuti Star ? Ophiuchi with a 2D Rotating Stellar Model
• The binary system of the spinning-top Be star Achernar
• Investigating the Circumstellar Disk of the Be Shell Star 48 Librae
• Be Stars: Rapidly Rotating Pulsators
• Massive stellar models: rotational evolution, metallicity effects
• Ellipsars: Ring-like explosions from flattened stars
• Physics of rotation: problems and challenges
• Nested spheroidal figures of equilibrium -- IV. On heterogeneous configurations
• Evolution and chemical and dynamical effects of high-mass stars