The remarkable properties of the symbiotic star AE Circinus

TL;DR

This study provides detailed optical, infrared, and long-term photometric observations of the symbiotic star AE Cir, revealing its unique variability, spectral features, and challenging existing models for symbiotic star outbursts.

Contribution

It introduces new observational data and analysis of AE Cir, identifying its classification as a yellow symbiotic star and highlighting its peculiar outburst behavior.

Findings

AE Cir exhibits outbursts lasting several years with a slow decline.

The star shows strong photometric signals at approximately 342 and 171 days.

Spectroscopy confirms AE Cir as a new member of s-type yellow symbiotic stars.

Abstract

We present new optical spectroscopy and photometry, 2MASS infrared observations and 24 years of combined AAVSO and AFOEV photometry of the symbiotic star candidate \ae. The long-term light curve is characterized by outbursts lasting several years and having a slow decline of $\sim 2 \times 10^{-4}$ mag/day. The whole range of variability of the star in the $V$ band is about 4 magnitudes. The periodogram of the photometric data reveals strong signals at $\sim$ 342 and 171 days. The presence of the emission feature at $\lambda$ 6830 \AA at minimum and the detection of absorption lines of a $\sim$ K5 type star confirm the symbiotic classification and suggest that AE Cir 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 $\lambda$ 6830 \AA emission feature and the weakness of the He II 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 \ae 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.