We present the results of our photometric and spectroscopic follow-up of the intermediate-luminosity optical transient AT~2017jfs .
At peak , the object reaches an absolute magnitude of M _ { g } = -15.46 \pm 0.15 mag and a bolometric luminosity of 5.5 \times 10 ^ { 41 } erg s ^ { -1 } .
Its light curve has the double-peak shape typical of luminous red novae ( LRNe ) , with a narrow first peak bright in the blue bands , while the second peak is longer-lasting and more luminous in the red and near-infrared ( NIR ) bands .
During the first peak , the spectrum shows a blue continuum with narrow emission lines of H and Fe II .
During the second peak , the spectrum becomes cooler , resembling that of a K-type star , and the emission lines are replaced by a forest of narrow lines in absorption .
About 5 months later , while the optical light curves are characterized by a fast linear decline , the NIR ones show a moderate rebrightening , observed until the transient disappears in solar conjunction .
At these late epochs , the spectrum becomes reminiscent of that of M-type stars , with prominent molecular absorption bands .
The late-time properties suggest the formation of some dust in the expanding common envelope or an IR echo from foreground pre-existing dust .
We propose that the object is a common-envelope transient , possibly the outcome of a merging event in a massive binary , similar to NGC4490-2011OT1 .