We used several data sets from the Plateau de Bure Interferometer to map the dimethyl ether emission in Orion-KL with different arcsec spatial resolutions and different energy levels to compare with our previous methyl formate maps. Our data show rem
arkable similarity between the dimethyl ether (CH3OCH3) and the methyl formate (HCOOCH3) distributions even on a small scale (1.8x0.8 or about 500 AU). This long suspected similarity, seen from both observational and theoretical arguments, is demonstrated with unprecedented confidence, with a correlation coefficient of maps of 0.8. A common precursor is the simplest explanation of our correlation. Comparisons with previous laboratory work and chemical models suggest the major role of grain surface chemistry and a recent release, probably with little processing, of mantle molecules by shocks. In this case the CH3O radical produced from methanol ice would be the common precursor (whereas ethanol, C2H5OH, is produced from the radical CH2OH). The alternative gas phase scheme, where protonated methanol CH3OH2+ is the common precursor to produce methyl formate and dimethyl ether through reactions with HCOOH and CH3OH, is also compatible with our data. Our observations cannot yet definitely allow a choice between the different chemical processes, but the tight correlation between the distributions of HCOOCH3 and CH3OCH3 strongly contrasts with the different behavior we observe for the distributions of ethanol and formic acid. This provides a very significant constraint on models.
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 fo
r 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 Nanc{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.
