The remarkable properties of the symbiotic star AE Circinus

We present new optical spectroscopy and photometry, Two-Micron All-Sky Survey (2MASS) infrared observations and 24 yr of combined American Association of Variable Star Observers (AAVSO) and Association Francaise des Observateurs d'Etoiles Variables (AFOEV) photometry of the symbiotic star candidate AECir. The long-term light curve is characterized by outbursts lasting several years and having a slow decline of ~2 × 10^-4 magd^-1. The whole range of variability of the star in the V band is about 4 mag. The periodogram of the photometric data reveals strong signals at ~342 and 171 d. The presence of the emission feature at λ6830 Å at minimum and the detection of absorption lines of a ~K5 type star confirm the symbiotic classification and suggest that AECir is a new member of the small group of s-type yellow symbiotic stars. We estimate a distance of 9.4 kpc. Our spectrum taken at the high state shows a much flatter spectral energy distribution, the disappearance of the λ6830 Å emission feature and the weakness of the HeII 4686 emission relative to the Balmer emission lines. Our observations indicate the presence of emission-line flickering in time-scales of minutes in 2001. The peculiar character of AECir is revealed in the visibility of the secondary star at the high and low state, the light curve resembling a dwarf nova superoutburst and the relatively short low states. The data are hard to reconciliate with standard models for symbiotic star outbursts.