Cyclotron features in the infrared spectrum of AM Herculis

We present spectroscopic observations of the magnetic cataclysmic variable AM Herculis covering the wavelength range $$1.0-2.5\enspace\mu\text{m}$$. The observations were obtained during the faint state of the system’s long-term light variations. During the faint phase of the binary cycle we see a spectrum which appears to be dominated by the radiation from the M-dwarf secondary, showing deep absorptions due to H₂O at around 1.4 and 1.9 μm. The spectrum can be well fitted with an M-dwarf model atmosphere for an effective temperature of 3250 K. During the bright phase of the binary cycle there is excess flux which we attribute to cyclotron radiation. If the faint phase, M-dwarf spectrum is subtracted from the bright phase, the resulting spectrum shows a series of maxima which can be identified with cyclotron emission harmonics from a field of 14.5 MG.