Semi-regular ( SR ) variables are not a homogeneous class and their variability is often explained due to pulsations and/or binarity .
This study focuses on IRAS 19135 + 3937 , an SRd variable with an infra-red excess indicative of a dusty disc .
A time-series of high-resolution spectra , UBV photometry as well as a very accurate light curve obtained by the Kepler satellite , allowed us to study the object in unprecedented detail .
We discovered it to be a binary with a period of 127 days .
The primary has a low surface gravity and an atmosphere depleted in refractory elements .
This combination of properties unambiguously places IRAS 19135 + 3937 in the subclass of post-Asymptotic Giant Branch stars with dusty discs .

We show that the light variations in this object can not be due to pulsations , but are likely caused by the obscuration of the primary by the circumbinary disc during orbital motion .
Furthermore , we argue that the double-peaked Fe emission lines provide evidence for the existence of a gaseous circumbinary Keplerian disc inside the dusty disc .
A secondary set of absorption lines has been detected near light minimum , which we attribute to the reflected spectrum of the primary on the disc wall , which segregates due to the different Doppler shift .
This corroborates the recent finding that reflection in the optical by this type of discs is very efficient .
The system also shows a variable H \alpha profile indicating a collimated outflow originating around the companion . IRAS 19135 + 3937 thus encompasses all the major emergent trends about evolved disc systems , that will eventually help to place these objects in the evolutionary context .