1998A&A...339...75P

The emission line star V439 Cyg (MWC 1015) dramatically changed its spectrum from late to early type in a few decades with line variability present at various levels. The star is a member of the peculiar young open cluster Berkeley 87 that contains, besides V439 Cyg, a few peculiar objects in a late stage of stellar evolution. A strong IR source is associated with the region surrounding V439 Cyg. The star has a peculiar position in the cluster HR diagram possibly due to anomalous reddening. We have analysed a collection of historical observations and collected new spectroscopic and photometric data on this unique object. We find several indications suggesting that the star has passed, in the last decades, through an instability phase with several features of the LBV behaviour. We suggest that its spectral change could be accounted for in the light of recent stellar models.