Trans-ethyl methyl ether in space

A new look at a complex molecule in selected hot core regions

¹ Department of Chemistry, UC Berkeley, Berkeley, CA 94720, USA
² Raymond and Beverly Sackler Laboratory for Astrophysics, Leiden Observatory, Leiden University, Postbus 9513, 2300 RA, Leiden, The Netherlands e-mail: fuchs@strw.leidenuniv.nl
³ I. Physikalisches Institut, Universität zu Köln, Zülpicher Str. 77, 50937 Köln, Germany e-mail: ufuchs@ph1.uni-koeln.de,giesen@ph1.uni-koeln.de
⁴ Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany e-mail: wyrowski@mpifr-bonn.mpg.de

Received: 9 June 2005
Accepted: 22 August 2005

Abstract

An extensive search for the complex molecule trans-ethyl methyl ether towards several hot core regions has been performed. Using the IRAM 30 m telescope and the SEST 15 m we looked at several frequencies where trans-ethyl methyl ether has strong transitions, as well as lines which are particularly sensitive to the physical conditions in which the molecule can be found. We included G34.26, NGC 6334(I), Orion KL, and W51e2 which have previously been proven to have a rich chemistry of complex molecules. Our observations cannot confirm the tentative Orion KL detection made by Charnley et al. (2001) within their stated column density limits, but we confirm the existence of the trans-ethyl methyl ether towards W51e2 with a column density of cm^-2. The dimethyl ether/methanol ratio of 0.6 as well as the newly found ethyl methyl ether/ethanol ratio of 0.13 indicate relative high abundances of ethers toward W51e2. Furthermore, the observation of ethyl methyl ether also confirms the importance of ethanol as a grain mantle constituent. We present new upper limits of around cm^-2 for the column densities of the molecule toward Orion KL, G34.26, NGC 6334(I) and estimate the column density towards SgrB2(N) to be of the same order. The W51e2 observations are discussed in more detail.