1996A&A...305L..57L

We have observed the circumstellar envelope of the carbon star U Cam in the HCN(J=1->0) and CN(N=1->0) lines using the IRAM Plateau de Bure interferometer. There is evidence of a two-envelope structure: an outer extended envelope, possibly a shell, with a radius of ∼7x10¹⁶cm, that expands with a velocity of ∼25km/s, surrounding an inner envelope with a radius of ∼6x10¹⁵cm and an expansion velocity of only ∼13km/s. Mass loss rate estimates based on these data alone are uncertain, but they suggest that the mass loss rate during the formation of the outer envelope was higher than during the present mass loss epoch. Thus, we have evidence for a significant variation in the mass loss characteristics of U Cam within the last 10³years.