Variations of the infrared polarisation of VY Canis Majoris

A REMARKABLE change in the infrared polarisation of VY Canis Majoris has been observed in 1974 and 1975. This star was found, in 1970, to have a large and peculiar polarisation1. Further observations carried out in 1971 and 1972 confirm the existence of a polarisation peak at 1.6 µm and a rapid rotation of the position angle of polarisation from visible to infrared wavelengths2–5 (see Fig. 1). The polarisation declines rapidly with wavelength from ultraviolet to infrared, having a dip near 1 µm, and rising further in the infrared, with peak at λ=1.6 µm. Corresponding to the rapid decrease in the polarisation, the position angle rotates by about 90°. Our latest observations show that the hump at 1.6 µm has disappeared.