Detection of Interstellar Acetone toward the Orion-kl Hot Core

We present the first detection of interstellar acetone [(CH3)2CO] toward the high mass star forming region Orion-KL and the first detection of vibrationally excited (CH3)2CO in the ISM. Using the BIMA Array, 28 emission features that can be assigned to 54 acetone transitions were detected. Furthermore, 37 of these transitions have not been previously observed in the ISM. The observations also show that the acetone emission is concentrated toward the hot core region of Orion-KL, contrary to the distribution of other large oxygen bearing molecules. From our rotational-temperature diagram we find a beam averaged (CH3)2CO column density of (2.0(0.3)− 8.0(1.2))× 10 cm and a rotational temperature of 176(48)-194(66) K. Subject headings: ISM:individual(Orion-KL)—ISM:molecules—radio lines:ISM The first detection of interstellar acetone [(CH3)2CO] was reported by Combes et al. (1987) and later confirmed by Snyder et al. (2002) towards the hot molecular core source Sgr B2(N-LMH). Previous to this paper, acetone had yet to be reported in any other high mass or low mass star forming region despite being structurally similar to dimethyl ether ((CH3)2O). Conversely, (CH3)2O has been detected in both low mass star forming regions including IRAS 16293-2422 (Cazaux et al. 2003) and high mass star forming regions including Sgr (Winnewisser & Gardner 1976) and Orion (Snyder et al. 1974). It seemed therefore likely that acetone may be prevalent in other star forming regions such as Orion-KL. Department of Astronomy, 1002 W. Green St., University of Illinois, Urbana IL 61801 email: [email protected], [email protected] NASA Goddard Space Flight Center, Computational and Information Sciences and Technologies Office, Code 606 , Greenbelt, MD 20771 email: [email protected] National Research Council Resident Research Associate National Radio Astronomy Observatory, Charlottesville, VA 22903 email: [email protected]