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IMAGING THE CIRCUMSTELLAR ENVELOPES AROUND EVOLVED STARS WITH THE SMA

  • HIRANO NAOMI (Academia Sinica, Institute of Astronomy and Astrophysics) ;
  • CHIU PO-JIAN (Academia Sinica, Institute of Astronomy and Astrophysics) ;
  • MULLER SEBASTIEN (Academia Sinica, Institute of Astronomy and Astrophysics) ;
  • TRUNG DINH-V (Academia Sinica, Institute of Astronomy and Astrophysics)
  • Published : 2005.06.01

Abstract

We present the high-resolution (2"-4") images of the molecular envelopes surrounding the evolved stars, V Hya, VY CMa, and ${\pi}^1$ Gru observed with the Submillimeter Array. The CO J=2-1 and 3-2 images of the carbon star V Hya show that the circumstellar structure of this star consists of three kinematic components; there is a flattened disk-like envelope that is expanding with a velocity of ${\~}16 km\;s^{-1}$, the second component is the medium-velocity wind having a deprojected velocity of 40-120 km $s^{-l}$ moving along the disk plane, and the third one is the bipolar molecular jet having an extreme velocity of 70-185 km $s^{-l}$. The axis of this high velocity jet is perpendicular to the plane of the disk-like envelope. We found that the circumstellar structure of the S-star ${\pi}^1$ Gru traced by the CO J =2-1 resembles that of V Hya quite closely; the star is surrounded by the expanding disk-like envelope and is driving the medium-velocity wind along the disk plane. We also obtained the excellent images of VY CMa with the CO and $^{13}CO$ J=2-1 and $SO\;6_5-5_4$ lines. The maps of three molecular lines show that the envelope has a significant velocity gradient in the east-west direction, suggesting that the envelope surrounding VY CMa is also flattened and expanding along its radial direction. The high-resolution images obtained with the SMA show that some AGB stars are associated with the asymmetric mass loss including the equatorial wind and bipolar jet.

Keywords

ISM: individual (V Hya, VY CMa, ;ISM: jets and outflows;ISM: molecules;stars: AGB and post-AGB

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