Morphological Changes, Evidence for a Collimating Disk, and Extremely Young Jetlike Components in the Planetary Nebula IC 4997

Details Morphological Changes, Evidence for a Collimating Disk, and Extremely Young Jetlike Components in the Planetary Nebula IC 4997 Morphological Changes, Evidence for a Collimating Disk, and Extremely Young Jetlike Components in the Planetary Nebula IC 4997

Mar 1998

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998apj...496..274m&link_type=abstract

Astrophysical Journal v.496, p.274

Astronomy and Astrophysics

Astronomy

12

Ism: Planetary Nebulae: Individual Alphanumeric: Ic 4997, Ism: Kinematics And Dynamics, Ism: Jets And Outflows, Stars: Mass Loss

Scientific paper

We present VLA-A radio continuum observations at 3.6 cm and 2 cm of the extremely young, double-shell planetary nebula IC 4997. A comparison of the new 3.6 cm map with that obtained in 1995 July shows that morphological changes have occurred in the nebula in ~=1.3 yr. These changes reveal themselves by the presence in the outer shell of several new bright compact regions, most of which are located along the major nebular axis. The observed changes suggest that a variable highly collimated stellar wind impinges on the outer shell and causes variation of the physical conditions in compact nebular regions. This mechanism is probably related to the origin of the microstructure in IC 4997. The inner shell has been resolved at 2 cm and shows an elliptical morphology with a deconvolved size of ~=0."12 x 0."09 (P.A. ~= 56 deg). Evidence for an extended, flat equatorial disk (size ~=1."4 x 0."22, P.A. ~= 125 deg) is found at 2 cm. The derived spectral index alpha (3.6-2 cm) map of the nebula reveals a compact (size ~= 0."5 x 0."2, P.A. ~= 125 deg), dense [Ne ~= (2-6) x 105 cm-3], optically thick ( tau 3.6 cm ~= 1-8) band that probably represents the innermost, densest regions of the extended disk. This disk can be identified as the collimating agent of both the inner and outer shells. In addition, extremely young bipolar jetlike features are observed along the major axis of the inner shell, exhibiting the typical properties of jetlike outflows in planetary nebulae.

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