IRAS21282+5050's Molecular Envelope Structure Revealed in 12CO

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Session 47 -- Planetary Nebulae
Display presentation, Tuesday, 10, 1995, 9:20am - 6:30pm

[47.01] IRAS21282+5050's Molecular Envelope Structure Revealed in 12CO

L. Likkel (Washington State University), M. Meixner (University of Illinois)

IRAS21282+5050 is an extremely young planetary nebula with several interesting characteristics, including a significant molecular circumstellar envelope. We have imaged IRAS21282+5050 in the CO (1-0) line with the BIMA millimeter array. With a synthesized beam size of about 3.3''x 2.5'', we find that the CO is located in a relatively symmetric shell surrounding the ionized region. Velocity maps show a clear central hole with a diameter of about 4'' x 6''. The hole is elongated in the same direction as the ionized region (roughly NW -- SE, diameter 3'' x 4''), in which the CO molecules have presumably been destroyed.

The CO (1-0) line was previously mapped (Shibata et al. 1988) with the Nobyama array, although they only detected half of the flux detected by single-dish observations. Our observations produced different results due to more complete sampling of spatial size structures: we see no evidence of a North-South disk, but find increased CO emission at the inner edge of the CO shell, along a roughly E -- W axis (perpendicular to the elongation of the ionized region). We note that infrared images also show peaks oriented roughly E--W (Meixner et al. 1993). We suggest that the infrared emission is from an inner torus of material which restricts the distance that ionizing radiation penetrates in the plane of the disk. Our initial results show that the LARGE SCALE emission from CO shows no bipolar symmetry. This is in keeping with evidence that circumstellar envelopes have overall spherical symmetry, and that a bipolar component forms only during the final stages of evolution toward the planetary nebula stage.

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