The young detached CO shell around U camelopardalis

We report IRAM Plateau de Pure interferometer observations of the carbon st ar U Cam in the CO(J = 1 --> 0) and CO(J = 2 --> 1) lines. The remarkable i mages show that U Cam is surrounded by a geometrically thin, similar to 10( 16) cm, shell of gas at a distance of similar to 6 x 10(16) cm from the sta r, that expands with a velocity of similar to 23 km s(-1). The estimated ma ss of the shell is low, similar to 10(-3) M.. In addition, we detect emissi on that peaks at the stellar position. From this we estimate a present mass loss rate and gas expansion velocity of similar to 2.5 x 10(-7) M. yr(-1) and 12 km s(-1), respectively. One possible explanation to the structure of the circumstellar medium is that the shell was produced during a very shor t period, similar to 150 yr, of high mass loss rate, similar to 10(-5) M. y r(-1) about 800 yr ago. U Cam may fit into the scenario where a helium-shel l flash modulates the mass loss rate on short times scales.