The discovery of two new bipolar proto-planetary nebulae: IRAS 16594-4656 and IRAS 17245-3951

We report the discovery of two new, bipolar proto-planetary nebulae (PPNs). Both are cool IRAS sources for which we have confirmed optical counterpart s by our 10 mu m observations. Ground-based visible and infrared photometry was combined with the IRAS photometry and spectroscopy to produce their sp ectral energy distributions (SEDs). These SEDs look like those of other PPN s, in particular those of bipolar PPNs. The central stars of both objects a re highly reddened and have color temperatures similar to 3000-4000 K. The nebulosities are dominated by scattered light, not emission lines as in pla netary nebulae. IRAS 16594-4656 appears to possess the 21 mu m emission fea ture seen previously in a dozen carbon-rich PPNs, along with the 8 mu m pol ycyclic aromatic hydrocarbon feature. Published millimeterwave observations support the notion that it is carbon-rich, while IRAS 17245-3951 appears t o be oxygen-rich. These facts confirm that these two objects are PPNs in tr ansition between the asymptotic giant branch and planetary nebula phases. H ubble Space Telescope imaging reveals that they are indeed bipolar nebulae. IRAS 17245 - 3951 clearly displays two lobes separated by a dust lane; thu s it is viewed nearly edge-on. Two jetlike features are seen in the souther n lobe of IRAS 17245-3951, similar to the base of the searchlight beams see n in AFGL 2688. IRAS 16594-4656 appears to be a bipolar nebulae viewed at a n intermediate orientation, and both the lobes and the central star can be seen. IRAS 16594-4656 therefore gives us our first clear example of the app arent morphology of a bipolar PPN viewed at an intermediate orientation. Th e addition of these objects to the list of bipolar PPNs confirms that such bipolar morphologies develop early in post-AGE evolution.