Discrete Source Survey of 6 GHz OH emission from PNe & pPNe and first 6 GHz images of K 3-35

TL;DR

This study conducts a high-sensitivity survey of 6 GHz OH maser emission in planetary nebulae, detecting rare maser lines in young nebulae and providing first images of K 3-35 at 6 GHz, advancing understanding of early nebular evolution.

Contribution

It presents the first 6 GHz images of K 3-35 and confirms rare OH maser emissions in young planetary nebulae, expanding knowledge of molecular envelopes in early stellar evolution.

Findings

Detected 6035 MHz OH maser emission in two young planetary nebulae.

Confirmed the first detection of 6035 MHz OH maser in Vy 2-2.

Provided the first 6 GHz images of K 3-35 showing maser and continuum features.

Abstract

The aim of this study is to investigate the physical properties of molecular envelopes of planetary nebulae in their earliest stages of evolution. Using the 100m telescope at Effelsberg, we have undertaken a high sensitivity discrete source survey for the first excited state of OH maser emission (J=5/2, 2PI3/2 at 6GHz) in the direction of planetary and proto-planetary nebulae exhibiting 18cm OH emission (main and/or satellite lines), and we further validate our detections using the Nan\c{c}ay radio telescope at 1.6-1.7GHz and MERLIN interferometer at 1.6-1.7 and 6GHz. Two sources have been detected at 6035MHz (5cm), both of them are young (or very young) planetary nebulae. The first one is a confirmation of the detection of a weak 6035MHz line in Vy 2-2. The second one is a new detection, in K 3-35, which was already known to be an exceptional late type star because it exhibits 1720MHz OH emission. The detection of 6035MHz OH maser emission is confirmed by subsequent observations made with the MERLIN interferometer. These lines are very rarely found in evolved stars. The 1612MHz masers surround but are offset from the 1720 and 6035MHz masers which in turn lie close to a compact 22GHz continuum source embedded in the optical nebula.