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J/A+A/314/871       V Hydrae (Kahane+ 1996)
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V Hydrae : the missing link between spherical red giants and bipolar 
planetary nebulae? Radio observations of the molecular envelope.
     Kahane C., Audinos P., Barnbaum C., Morris M.
    <Astron. Astrophys. 314, 871 (1996)>
    =1996A&A...314..871K      (SIMBAD/NED BibCode)
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ADC_Keywords: Stars, giant
Keywords: stars: V Hya; AGB; post-AGB; circumstellar matter; mass loss
          carbon - radio lines: stars

Abstract:
    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^-6^M_{sun}_/yr), with about 90% of the molecular gas
    expelled in the high-velocity jet. The circumstellar envelope around
    V Hya contains ~2.1x10^-3^M_{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.

Objects:
    -----------------------------------------
        RA   (2000)   DE       Designation(s)
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     10 51 37.27  -21 15 01.1  V Hya
    -----------------------------------------

File Summary:
--------------------------------------------------------------------------------
 FileName    Lrecl    Records    Explanations
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ReadMe          80          .    This file
vhyafig1.ps     81       6680    *PostScript file of fig1
vhyafig2.ps     81       4156    *PostScript file of fig2
vhyafig3.ps     81       3607    *PostScript file of fig3
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Note on vhyafig1.ps: Comparison of two methods used to recenter the 
    individual maps. The black squares on the spectral maps correspond to
    the same position in the envelope, according to a visual comparison of
    the line shapes of both maps. It means that the (0,0) position of the
    map No 5 is shifted by +5arcsec in declination compared to the (0,0)
    position of the map No 9. The contours represent the intensity in the
    blue peak of the lines for each map. The dotted lines indicate the
    maximum of each map. To make the maxima coincide, map No 5 must be
    shifted by -0.75arcsec in right ascension and +4.75arcsec in declination.
Note on vhyafig2.ps: 12CO(2-1) emission towards the circumstellar envelope 
    of V Hya. Due to the shift-and-add technique used to reduce the data,
    the exact coordinates of the (0,0) position of the map are uncertain
    but should be close to the coordinates of the star:
    alpha(1950)=10h49m11.3s, delta(1950)=-20:59:05.0. Linear baselines
    have been subtracted from the spectra. The velocity resolution is
    1.3km/s.
Note on vhyafig3.ps: The same as Fig. 2 for the 12CO(1-0) emission. 
    The velocity resolution is 1.6km/s.
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Acknowledgements: Claudine Kahane <kahane@gag.observ-gr.fr>
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(End)                                         Patricia Bauer [CDS]   03-May-1996