Achernar: Rapid Polarization Variability as Evidence of Photospheric and Circumstellar Activity

Abstract

We present the results of a high accuracy ($\sigma \approx 0.005$) polarization monitoring of the Be Star Achernar that was carried out between July 7th and November 5th, 2006. Our results indicate that, after a near quiescent phase from 1998 to 2002, Achernar is presently in an active phase and has built a circumstellar disk. We detect variations both in the polarization level and position angle in timescales as short as one hour and as long as several weeks. Detailed modeling of the observed polarization strongly suggests that the short-term variations originate from discrete mass ejection events which produce transient inhomogeneities in the inner disk. Long-term variations, on the other hand, can be explained by the formation of an inner ring following one or several mass ejection events.

arXiv comment16 pages, 5 figures, Accepted to ApJ

References in corpus (5)

• 9286 Stars: An Agglomeration of Stellar Polarization Catalogs
• Be-star rotation: how close to critical?
• NLTE Monte Carlo Radiative Transfer: I. The Thermal Properties of Keplerian Disks around Classical Be Stars
• A Statistical Study of Threshold Rotation Rates for the Formation of Disks around Be Stars
• Properties of the $\delta$ Scorpii Circumstellar Disk from Continuum Modeling

Cited by in corpus (30)

• Classical Be Stars: Rapidly Rotating B Stars with Viscous Keplerian Decretion Disks
• The life cycles of Be viscous decretion discs: fundamental disc parameters of 54 SMC Be stars
• Short-term variability and mass loss in Be stars I. BRITE satellite photometry of $\eta$ and $\mu$ Centauri
• Confirmation of the magnetic oblique rotator model for the Of?p star HD 191612
• Disk Loss and Disk Renewal Phases in Classical Be Stars I: Analysis of Long-Term Spectropolarimetric Data
• The linear polarization of nearby bright stars measured at the parts per million level
• On the Determination of the Rotational Oblateness of Achernar
• Dynamical Evolution of Viscous Disks around Be Stars. II : polarimetry
• The life cycles of Be viscous decretion discs: The case of ω CMa
• The linear polarisation of southern bright stars measured at the parts-per-million level
• Periodic Activities of Repeating Fast Radio Bursts from Be/X-ray Binary Systems
• Short-term variability and mass loss in Be stars III. BRITE and SMEI satellite photometry of 28 Cygni
• Disk-Loss and Disk-Renewal Phases in Classical Be Stars II. Contrasting with Stable and Variable Disks
• Towards Understanding The B[e] Phenomenon: IV. Modeling of IRAS 00470+6429
• The Be Star 66 Ophiuchi: 60 Years of Disk Evolution
• A Multi-observing-technique Study of the Dynamical Evolution of the Viscous Disk around the Be Star $\omega$ CMa
• Short-term variability and mass loss in Be stars IV. Two groups of closely spaced, approximately equidistant frequencies in three decades of space photometry of $\nu$ Puppis (B7-8 IIIe)
• A New Diagnostic of the Radial Density Structure of Be Disks
• The Role of Disk Tearing and Precession in the Observed Variability of Pleione
• Polarimetric observations of $\sigma$ Orionis E
• Variable rotational line broadening in the Be star Achernar
• Multitechnique testing of the viscous decretion disk model I. The stable and tenuous disk of the late-type Be star $\beta$ CMi
• The binary system of the spinning-top Be star Achernar
• VLTI/PIONIER images the Achernar disk swell
• Infrared Excess in the Be Star Delta Scorpii
• The Complex Circumstellar and Circumbinary Environment of V356 Sgr
• Untangling magnetic massive star properties with linear polarization variability and the Analytic Dynamical Magnetosphere model
• Red Be stars in the Magellanic Clouds?
• Polarization position angle standard stars: a reassessment of $\theta$ and its variability for seventeen stars based on a decade of observations
• Long-term optical variability of high-mass X-ray binaries. III. Polarimetry