CONDENSATION OF DUST AROUND THE WOLF-RAYET STAR WR 125

Infrared photometry of the WC7-type Wolf-Rayet star WR 125 (MR 93) in 1981-91 shows a 10-fold rise in the 3-4 mum flux during 1990-91. This, together with observations at longer wavelengths, is interpreted in terms of the condensation of dust in its wind, similar to the events observed from episodic dust-making WR stars like WR 48a in 1979-80 and WR 140 in 1977 and 1985. Dust condensation started in 1990.6 and has continued for at least a year at a rate of 2.3 x 10(-7) M. yr-1, about 0.4 per cent of the mass-loss rate. The pre-condensation photometry of its stellar wind indicates that WR 125 is 3.5 times as distant as WR 140, namely 4.7 kpc away. Radio observations at 2, 6 and 20 cm in 1985 are modelled in terms of a component from the stellar wind and an embedded non-thermal source of intrinsic spectrum S(nu) is-proportional-to nu--0.6 and suffering circumstellar extinction. Reobservation of the 6-cm flux in 1988 showed that this had fallen significantly to a level little more than the free-free emission from the stellar wind, indicating severe attenuation of the non-thermal source. The optical emission-line spectrum of WR 125 is diluted almost as much as that of WR 140, presumably by the continuum of a hot companion, although we have been unable to find any absorption lines from it in the lambdalambda4370-4770 region. From the profile of the He I 1.083-mum line in our infrared spectrum, a wind velocity of 2900 km s-1 is determined, similar to that of WR 140, suggesting that the new dust shell will be dissipated on a time-scale (approximately 4 yr) comparable to that of WR 140.