Context : R Coronae Borealis stars ( RCB ) are a rare type of evolved carbon-rich supergiant stars that are increasingly thought to result from the merger of two white dwarfs , called the Double degenerate scenario .
This scenario is also studied as a source , at higher mass , of type Ia Supernovae ( SnIa ) explosions .
Therefore a better understanding of RCBs composition would help to constrain simulations of such events .

Aims : We searched for and studied RCB stars in the EROS Magellanic Clouds database .
We also extended our research to DY Per type stars ( DYPers ) that are expected to be cooler RCBs ( T \sim 3500 K ) and much more numerous than their hotter counterparts .
With the aim of studying possible evolutionary connections between RCBs and DYPers , and also ordinary carbon stars , we compared their publically available broad band photometry in the optical , near , and mid-infrared .

Methods : The light curves of \sim 70 millions stars , monitored for 6.7 years ( from July 1996 to February 2003 ) , have been analysed to search for the main signature of RCBs and DYPers : a large ( up to 9 mags ) drop in luminosity .
Carbon stars with fading episodes were also found by inspecting numerous light curves of objects that presented an infrared excess in the 2MASS and Spitzer- SAGE and S ^ { 3 } MC databases .
Follow-up optical spectroscopy was used to confirm each photometric candidate found .

Results : We have discovered and confirmed 6 new Magellanic Cloud RCB stars and 7 new DYPers , but also listed new candidates : 3 RCBs and 14 DYPers .
Optical and infrared colour magnitude diagrams that give new insights into these two sets of stars are discussed .
We estimated a range of Magellanic RCB shell temperatures between 360 and 600 K .

Conclusions : We confirm the wide range of absolute luminosity known for RCB stars , M _ { V } \sim -5.2 to -2.6 .
Our study further shows that mid-infrared surveys are ideal to search for RCB stars , since they have thinner and cooler circumstellar shells than classical post-AGB stars .
In addition , by increasing the number of known DYPers by \sim 400 % , we have been able to shed light on the similarities in the spectral energy distribution between DYPers and ordinary carbon stars .
We also observed that DYPer circumstellar shells are fainter and hotter than those of RCBs .
This suggests that DYPers may simply be ordinary carbon stars with ejection events , but more abundance analysis is necessary to give a status on a possible evolutionnary connexion between RCBs and DYPers .