1999A&A...351L...1L

We report IRAM Plateau de Bure interferometer observations of the carbon star U Cam in the CO(J=1-0) and CO(J=2-1) lines. The remarkable images show that U Cam is surrounded by a geometrically thin, ∼10¹⁶cm, shell of gas at a distance of ∼6x10¹⁶cm from the star, that expands with a velocity of ∼23km/s. The estimated mass of the shell is low, ∼10^–3M_☉. In addition, we detect emission that peaks at the stellar position. From this we estimate a present mass loss rate and gas expansion velocity of ∼2.5x10^–7M_☉/yr and 12km/s, respectively. One possible explanation to the structure of the circumstellar medium is that the shell was produced during a very short period, ∼150yr, of high mass loss rate, ∼10^–5M_☉/yr, about 800yr ago. U Cam may fit into the scenario where a helium-shell flash modulates the mass loss rate on short times scales.