Symbiotic stars (SySts) are long-period interacting binaries composed of a hot compact star and an evolved giant star, whose mutual interaction via accretion processes is at the origin of a tangled network of gas and dust nebulae. They represent unique laboratories for studying a variety of important astrophysical problems and their reciprocal influence, and have also been proposed as possible progenitors of SNIa. Presently, we know 257 SySts in the Milky Way and 69 in external galaxies. However, these numbers are still in striking contrast with the predicted population of SySts in our Galaxy that, according to different theoretical estimates, may oscillate between 10³ and a few 10⁵. One of the reasons for this embarrassing discrepancy lies in the very same definition of SySts, historically based on purely spectroscopic criteria. Because of several other astrophysical sources that mimic SySt colours, no photometric diagnostic tool has so far demonstrated the power to unambiguously identify a SySt, thus making the recourse to costly spectroscopic follow-up still inescapable.

In this talk I will present the concept, commissioning and science verification phase, as well as the very first scientific results, of RAMSES II – a Gemini Observatory Instrument Upgrade Project that has provided the GMOS instruments at both Gemini telescopes with a set of narrow-band filters centered on the Raman OVI 6830 Å band. RAMSES II aims at discovering and characterizing the hidden population of SySs in the Milky Way and in Local Group galaxies via Raman OVI narrow-band imaging, providing the astronomical community with the first purely photometric tool for hunting SySts in the local Universe.Milky Way and in Local Group galaxies via Raman OVI narrow-band imaging, providing the astronomical community with the first purely photometric tool for hunting SySts in the local Universe.