2007AJ....134.1877K

We present an extended optical spectropolarimetry of R CrB from 1998 January to 2003 September. The polarization was almost constant in the phase of maximum brightness, being consistent with past observations. We detected, however, temporary changes of the polarization (∼0.5%) in 2001 March and August, which were the first detections of large polarization variability in R CrB near maximum brightness. The amplitude and the position angle of the ``transient polarization'' were almost constant with wavelength in both events. There was a difference of about 20° in the position angle between the two events. Each event could be explained by light scattering due to a short-lived dust puff occasionally ejected off the line of sight. The flatness of the polarization versus the wavelength suggests that the scatterer is a mixture of dust grains of various sizes. The rapid growth and fading of the transient polarization favor the phenomenological model of dust formation near the stellar photosphere (e.g., within two stellar radii) proposed for the time evolution of brightness and chromospheric emission lines during deeply declining periods, although the fading timescale can hardly be explained by a simple dispersal of an expanding dust puff with a velocity of ∼200-350 km/s. A higher expansion velocity or some mechanism to destroy the dust grains is needed.