We have detected asymmetry in the symbiotic star CHÂ Cyg through the measurement of precision closure–phase with the IONIC beam combiner , at the IOTA interferometer .
The position of the asymmetry changes with time and is correlated with the phase of the 2.1–yr period found in the radial velocity measurements for this star .
We can model the time–dependent asymmetry either as the orbit of a low–mass companion around the MÂ giant or as an asymmetric , 20 % change in brightness across the MÂ giant .
We do not detect a change in the size of the star during a 3 year monitoring period neither with respect to time nor with respect to wavelength .
We find a spherical dust–shell with an emission size of 2.2 \pm 0.1Â D _ { * } Â FWHM around the MÂ giant star .
The star to dust flux ratio is estimated to be 11.63 \pm 0.3 .
While the most likely explanation for the 20 % change in brightness is non–radial pulsation we argue that a low–mass companion in close orbit could be the physical cause of the pulsation .
The combined effect of pulsation and low–mass companion could explain the behaviour revealed by the radial–velocity curves and the time–dependent asymmetry detected in the closure–phase data .
If CHÂ Cyg is a typical long secondary period variable then these variations could be explained by the effect of an orbiting low–mass companion on the primary star .