We report new spectroscopic observations of the magnetic Of ? p star HD 148937 obtained since 2015 that differ qualitatively from its extensive historical record of weak , periodic spectral variations .
This remarkable behaviour represents clear evidence for an unprecedented change in the character of variability of the star .
In this paper we describe the new spectral properties and compare them to the previous line profiles .
Based on measurements of the radial velocities of the C iii /N iii emission lines near 4640 Å and the C iv absorption lines near 5800 Å , we infer that HD 148937 is likely a high-mass , double-lined spectroscopic binary .
Combining the spectroscopic orbit with an archival interferometric measurement of the apparent separation of the equal-brightness components , we tentatively conclude that HD 148937 consists of two O-type stars with masses of approximately 34 and 49 ~ { } M _ { \odot } , orbiting in an eccentric ( e = 0.75 ) , long-period ( P _ { orb } \sim 26 y ) orbit .
We discuss the potential relationship of the binary system to the peculiar properties of HD 148937 , and propose future observations to refine the orbital and stellar properties .