Astronomy and Astrophysics – Astronomy
Scientific paper
Oct 2000
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2000aas...196.4306h&link_type=abstract
American Astronomical Society, 196th AAS Meeting, #43.06; Bulletin of the American Astronomical Society, Vol. 32, p.1283
Astronomy and Astrophysics
Astronomy
Scientific paper
We report the discovery of a collimated bipolar outflow emerging from a visibled isk around the proto-planetary nebula (PPN) IRAS 17106-3046. The radius of the disk, estimated to be 3000 AU at a distance of 4 kpc, is too large for it to be a Keplerian disk created by accretion. The radial intensity profile of the disk suggests that it is consistent with an expanding torus. In contrast to the open-end, butterfly-like lobes commonly seen in bipolar planetary nebulae, the lobes of IRAS 17106-3046 have pointed ends, suggesting a recently-formed jet breaking out of the lobes. IRAS 17106-3046 therefore could represent the earliest stage of the bipolar shaping process during the transition from an asymptotic giant branch star to a planetary nebula. In addition, concentric circumstellar arcs have been discovered using the HST in two more PPNs, IRAS 16594-4656 and 20028+3910. This raises to five the number of PPNs in which such arcs have been detected, and suggests that they are not rare and may even be common features. All five of these PPNs display a bipolar morphology, but this may be the result of a selection effect in which deeper images are taken of bipolar PPNs in which the central star is obscured. Two pair of oppositely-directed ``searchlight beams'' are seen in IRAS 20028+3910, similar to those seen in the AFGL 2688 and IRAS 17150-3224. The presence of these circular arcs in PPNs with a variety of viewing orientations implies that they are illuminated portions of spherically shells, viewed in scattered light. This suggests that the mass loss process is spherically symmetric over most of the lifetime of the progentor AGB star, and the transition to bipolar morphology occurs over a short period at the end of the AGB evolution. Support for this work was provided by NASA to BJH through grant number GO-08210.01-97A from the STScI, which is operated by the AURA, Inc., under NASA contract NAG5-26555, and by a grant to SK from the NSERC of Canada.
Hrivnak Bruce J.
Kwok Sun
Su Kate Y. L.
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