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M. Lindqvist, R. Lucas, H. Olofsson,
A. Omont, K. Eriksson, B. Gustafsson
Sterrewacht Leiden, Postbus 9513, 2300 RA Leiden, The Netherlands
IRAM, 300 rue de la Piscine, F-38406 St Martin d'Heres Cedex, France
Stockholm Observatory, S-13336, Saltsjöbaden, Sweden
Institut d'Astrophysique de Paris, CNRS, 98 bis bd Arago, F-75014 Paris, France
Astronomical Observatory, Box 515, S-75120 Uppsala, Sweden
Abstract: We have observed the circumstellar envelope of the carbon star U Cam
in the () and () 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 cm, that expands with a velocity of , surrounding an inner envelope with a radius of cm and an expansion velocity of only . 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 10 years.
Figure: a) Velocity-channel maps of the
() emission towards U Cam.
Contours levels are
, , , ,
0.05, 0.077, 0.118, 0.18, 0.276, 0.424, 0.649, 0.996, 1.526 and
2.34 Jy/beam, i.e., spacing is logarithmic.
Negative contours are dashed. The synthesized
CLEAN beam (shown at the half power contour) is .
The last panel shows the uv plane coverage.
The HCN spectrum obtained from the map data. c) Size
the inner (squares) and outer (circles) envelopes (see text for details).
The small dots give the relation