NARROW-BAND HST IMAGERY OF THE YOUNG PLANETARY-NEBULA HENIZE-1357

We present HST Planetary Camera observations showing the first optical ly resolved images of the planetary nebula Henize 1357. The small size of this object has heretofore precluded optical investigations of its morphology. In Hbeta, He 3-1357 appears to have an equatorial ring of enhanced density tilted approximately 56-degrees from our line of sig ht. In addition, there are bubbles of gas above and below the ring wit h areas of decreased brightness near the poles where a fast stellar wi nd has broken through the red giant envelope. He 3-1357 has been evolv ing very rapidly, becoming a planetary nebula only within the past few decades. Assuming a distance of 5.6 kpc, the radius of the nebula is 0.02 pc, implying an expansion age of 2650 yr, although it has been io nized for no more than 40 yr. The Hbeta flux is now 5.8 x 10(-11) ergs cm-2 s-1 which implies an ionized mass of 0.2 M., log L/L. = 3.7, an d a core mass of 0.59 M..