IRAS F18187+6304: a puzzling emission line star

We observed in the optical range the strong infrared source IRAS F18187+6304 in the context of a program aimed to clarify the nature of the stellar objects of the Byurakan Infrared Source catalogue. The optical spectrum is characterized by continuum and absorption lines typical of early K-type giants plus a few permitted and forbidden emission lines. The sparse optical photometry did not put in evidence strong variations during the last 50 years. Our repeated observations indicate a substantial stability of the spectra and a monotonic increase of the luminosity in the BVR bands of about 0.4 magnitudes between Summer 2007 and Fall 2008. From a high resolution spectrum we measured a heliocentric radial velocity of -25 km/s and discovered a complex NaI-D structure resembling that of some T Tauri stars; the infrared CaII triplet is in absorption. A strong IR excess in the IRAS bands indicates a substantial quantity of circumstellar dust and gas. IRAS F18187+6304 is an isolated star at quite high galactic latitude, far from any star forming region. All these characteristics make this object an intriguing case of difficult interpretation. The preliminary results are discussed in the framework of the available synthetic energy distribution and accretion models.