Other
Scientific paper
May 1996
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996ycat..33140871k&link_type=abstract
VizieR On-line Data Catalog: J/A+A/314/871. Originally published in: 1996A&A...314..871K
Other
Stars: Giant
Scientific paper
We have performed fully sampled mapping of CO (J=1-0) and (J=2-1) emission around the red giant carbon star V Hya, with the IRAM 30m telescope. The velocity structure of the lines reveals two symmetric high velocity wings that we interpret as arising from a bipolar flow. Exactly between the red and the blue cones lies a low velocity component showing the same symmetry axis. We suggest that this component is a moderately oblate spheroid with biconical holes centered on the minor axis, or a thick torus with the same symmetry axis as the bipolar flow. The high signal-to-noise ratio and spectral resolution of the data allow a detailed comparison of the observed lines with a model of the envelope. Using this model, we derive the geometrical and kinematical parameters of the bipolar flow: it appears to have a wide opening angle (65deg) and shows a radially decreasing velocity law, starting at a velocity of at least 50km/s at the flow inner radius. We suggest that this behaviour is due to an increase with time of the flow ejection velocity close to the star. In contrast, the low-velocity component expands at a constant velocity of 7.5km/s. From our model we also derive the total mass loss rate of V Hya (~1.5x10-6M&sun;/yr), with about 90% of the molecular gas expelled in the high-velocity jet. The circumstellar envelope around V Hya contains ~2.1x10-3M&sun;, with about four times more gas in the bipolar flow than the low-velocity component. We compare our observations with other evidence for asymmetric mass loss from V Hya. Considering also the star's fast rotation revealed by the photospheric lines, we conclude that V Hya is probably experiencing the short binary common envelope evolution phase between the AGB and the planetary nebula stage, where highly asymmetric mass loss develops. (1 data file).
Audinos P.
Barnbaum Cecilia
Kahane Claudine
Morris Marita
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