Achernar: Rapid Polarization Variability as
Evidence of Photospheric and Circumstellar Activity
A. C. Carciofi,1
A. M. Magalhães,1
N. V. Leister,1
J. E. Bjorkman,2 &
R. S. Levenhagen3
1
Instituto de Astronomia, Geofísica e Ciências
Atmosféricas, Universidade de São Paulo, Rua do
Matão 1226, Cidade Universitária, São Paulo,
SP 05508-900, Brazil
2
University of Toledo, Department of Physics & Astronomy MS111,
2801 W. Bancroft Street, Toledo, OH 43606 USA
3
Centro Universitário Franciscano - UNIFRA,
Rua dos Andradas, 1614, Santa Maria, RS 97010-032, Brazil
We present the results of a high accuracy
(σ  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.
Accepted by ApJL
Preprints from
carciofi@usp.br
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