The infrared variability of OH 0739-14.

JHKL infrared observations show that OH 0739-14 contains a long-period variable (P = 648 days, ΔK = 1.0 mag). There is some evidence that this is a supergiant system resembling VY CMa. The phasing of the infrared variations predicted by Morris &Bowers on the assumption that the OH maser is saturated and pumped by the infrared flux, is confirmed. Variations of the star (at J) lag behind the variations of the heated dust shell (at L). This is expected if the heating of the dust is due to stellar radiation in the 0.6 to 1.0 μm wavelength range. Light travel-time effects may also be important.