We have discovered a conspicuous unidentified variable feature near 6307 Å in the spectrum of \eta Carinae which is spatially unresolved from the central star and its wind ( r \lesssim 200–300 AU ) .
It is significant for two reasons : such prominent unidentified lines are now rare in this object , and this feature varies strongly and systematically .
It exhibits a combination of characteristics which , so far as we know are unique in \eta Carinae ’ s spectrum .
It may provide insights into the recurrent spectroscopic events and the star ’ s long-term brightening .