A Collimated, Ionized Bipolar Structure and a High Density Torus in the Planetary Nebula IRAS 17347-3139

Abstract

We present observations of continuum (λ = 0.7, 1.3, 3.6, and 18 cm) and OH maser (λ = 18 cm) emission toward the young planetary nebula IRAS 17347–3139, which is one of the three planetary nebulae that are known to harbor water maser emission. From the continuum observations, we show that the ionized shell of IRAS 17347–3139 consists of two main structures: one extended (size ~ 1".5) with bipolar morphology along P.A.= –30°, elongated in the same direction as the lobes observed in the near-infrared (NIR) images, and a central compact structure (size ~ 0".25) elongated in the direction perpendicular to the bipolar axis, coinciding with the equatorial dark lane observed in the NIR images. Our image at 1.3 cm suggests the presence of dense walls in the ionized bipolar lobes. We estimate for the central compact structure a value of the electron density at least ~5 times higher than in the lobes. A high-resolution image of this structure at 0.7 cm shows two peaks separated by about 0".13 (corresponding to 100-780 AU, using a distance range of 0.8-6 kpc). This emission is interpreted as originating in an ionized equatorial torus-like structure, from whose edges the water maser emission might be arising. We have detected weak OH 1612 MHz maser emission at V(LSR) ~ –70 km s–1 associated with IRAS 17347–3139. We derive a 3σ upper limit of < 35% for the percentage of circularly polarized emission. Within our primary beam, we detected additional OH 1612 MHz maser emission in the local standard of rest velocity ranges –5 to –24 and –90 to –123 km s–1, associated with the sources J17380406–3138387 and OH 356.65–0.15, respectively.