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R. Sahai, C. Sanchez-Contreras (JPL/ Caltech), V. Bujarrabal, A. Castro-Carrizo (Observatorio Astronomico Nacional, Spain)
The Frosty Leo Nebula (IRAS09371+1212) is a bipolar nebula bisected by a dense edge-on torus/disk around a star believed to be in the short transition phase between the AGB and planetary nebula evolutionary phases. This well-studied pre-planetary nebula is noteworthy for showing the presence of water ice in its dust grains and possessing a strongly point-symmetric morphology. In a recent study (Sahai et al. 2000), we reported (a) the discovery of multiple low-latitude jet-like features in the inner regions of this object using images from the Hubble Space Telescope, and (b) 12CO and 13CO J=1-0 and 2-1 lines profiles (obtained with the IRAM 30-m radio telescope) implying the presence of a compact (5-10 arcsec) expanding molecular envelope with at least two kinematic components.
Here we report high-resolution (2''.3\times2''.9) observations of the Frosty Leo molecular envelope, obtained recently with the Caltech mm-wave interferometer at Owens Valley Radio Observatory. The velocity-integrated CO J=1-0 map shows a compact (FWHM\approx5''\times6''.5) source; maps in individual velocity channels within the line-profile show the presence of complex substructures, including knots and elongations. We find significant morphological changes between successive velocity channels (2.6 km\,s-1 wide), indicating that either some of the kinematic structure has not been adequately resolved, and/or that the source contains multiple kinematic components with different morphologies in projection (e.g. many jet-like outflows with different orientations). A detailed correlation between the features seen in the HST images and that seen in our OVRO maps has not been possible so far (first, the latter are still very preliminary, and second, the intrinsic source structure and velocity gradients are quite complex). However, the OVRO maps clearly show that the molecular envelope in Frosty Leo departs strongly from the classical picture of a spherical shell expanding at constant speed. These departures probably result from the action of high-velocity gas in collimated jet-like outflows (several of which are seen in our HST images) on the dense slow wind from the progenitor AGB star.
This work is funded in part by a NASA Long Term Space Astrophysics Grant to RS.
References: Sahai, R., Bujarrabal, V., Castro-Carrizo, A., & Zijlstra, A. 2000, A&A, 360, L9
The author(s) of this abstract have provided an email address for comments about the abstract: sahai@grandpa.jpl.nasa.gov