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Session 7 - Planetary & Other Nebulae.
Display session, Monday, June 09
South Main Hall,
We present J and K band near-infrared images of the young bipolar planetary nebula M1-91. The images were obtained using the GRIM II near-IR camera on the ARC 3.5 meter telescope at Apache Point Observatory. At optical wavelengths, M1-91 appears as two roughly, symmetric lobes of nebulosity with a bright central source located between the lobes. Further, the bipolar lobes contain knots or brightness enhancements that are point symmetric about the nucleus (Goodrich 1991). The morphology of M1-91 in the J band images is similar to that seen in optical. The nebula is obviously bipolar and the lobes contain point symmetric bright knots. On the other hand, the bright nucleus between the bipolar lobes dominates the K band images. The bright knots are still clearly visible at K, but the overall shape of the nebula is more amorphous. While the overall morphology of M1-91 changes as we look farther into the infrared, the knots of emission are plainly visible in both the optical and near-IR images. This suggest that these features may be formed by a different mechanism. At short wavelengths the bipolar lobes of M1-91 act as reflection nebulae, scattering light from the heavily obscured central regions into our line of sight and producing the overall bipolar appearance of the object. The bipolar lobes are highly polarized (P >20%) at optical wavelengths (Trammell 1994) supporting this idea. On the other hand, we propose that the bright knots seen in the lobes of M1-91 result from emission produced locally in the lobes, not via scattering. FLIER's have been seen in numerous planetary nebulae and may be related to collimated outflows in these objects (e.g. Balick et al. 1994). HST images of M1-92, a younger cousin of M1-91, reveal a jet in the bipolar lobes of this proto-planetary nebula (Trammell and Goodrich 1996). We suggest that the knots seen in the lobes of M1-91 result from the impact of a similar outflow with the bipolar lobes. We discuss several possible mechanisms that could produce such an outflow.
