Comparative study of complex N- and O-bearing molecules in hot molecular cores

Abstract

Aims. We have observed several emission lines of two Nitrogen-bearing (C 2 H 5 CN and C 2 H 3 CN) and two Oxygen-bearing (CH 3 OCH 3 and HCOOCH 3 ) molecules towards a sample of well-known hot molecular cores (HMCs) in order to check whether the chemical differentiation seen in the Orion-HMC and W3(H 2 O) between O-and N-bearing molecules is a general property of HMCs. Methods. With the IRAM-30m telescope we have observed 12 HMCs in 21 bands, centered at frequencies from 86 250 to 258 280 MHz. Results. In six sources, we have detected a number of transitions sufficient to derive their main physical properties. The rotational temperatures obtained from C 2 H 5 CN, C 2 H 3 CN and CH 3 OCH 3 range from ∼100 to ∼150 K in these HMCs. The total column densities of these molecules are of the order of ∼10 15 −10 17 cm −2 . Single Gaussian fits performed to unblended lines show a marginal difference in the line peak velocities of the C 2 H 5 CN and CH 3 OCH 3 lines, indicating a possible spatial separation between the region traced by the two molecules. On the other hand, neither the linewidths nor the rotational temperatures and column densities confirm such a result. The average molecular abundances of C 2 H 5 CN, C 2 H 3 CN and CH 3 OCH 3 are in the range ∼10 −9 −10 −10 , comparable to those seen in the Orion hot core. In other HMCs Bisschop et al. 2007 found comparable values for C 2 H 5 CN but values ∼2.5 times larger for CH 3 OCH 3 . By comparing the abundance ratio of the pair C 2 H 5 CN/C 2 H 3 CN with the predictions of theoretical models, we derive that the age of our cores ranges between 3.7 and 5.9 × 10 4 yr. Conclusions. The abundances of C 2 H 5 CN and C 2 H 3 CN are strongly correlated, as expected from theory which predicts that C 2 H 3 CN is formed through gas phase reactions involving C 2 H 5 CN . A correlation is also found between the abundances of C 2 H 5 CN and CH 3 OCH 3 , and C 2 H 3 CN and CH 3 OCH 3 . In all tracers the fractional abundances increase with the H 2 column density while they are not correlated with the gas temperature. On average, the chemical and physical differentiation between O-and N-bearing molecules seen in Orion and W3(H 2 O) is not revealed by our observations. We believe that this is partly due to the poor angular resolution of our data, which allows us to derive only average values over the sources of the discussed parameters.

A high-resolution study of complex organic molecules in hot cores

“…Methylene amidogen has previously been found in the cold core TMC-1 (Ohishi et al 1994) and methyl formate and vinyl alcohol have previously been detected in hot cores (Fontani et al 2007;Turner & Apponi 2001). Using criterion (iii) from Section 4 we can rule out methylene amidogen as there are several expected transitions in the frequency range of our observations that are not seen.…”

Chemistry of massive young stellar objects with a disk-like structure

“…Observations of CH 3 CN transitions show a References. (a) Cesaroni et al (1997), (b) Moscadelli et al (2011), (c) Leurini et al (2007), (d) Sridharan et al (2002), (e) Xu et al (2011), ( f ) Cesaroni et al (1994b), (g) Churchwell et al (1990), (h) Fontani et al (2007).…”

“…Millimeter lines from complex organic molecules are widely associated with high-mass star forming regions and indeed form one of the signposts of the deeply embedded phase of star formation (e.g., Blake et al 1987;Hatchell et al 1998;Gibb et al 2000;Fontani et al 2007;Requena-Torres et al 2008;Belloche et al 2009;Zernickel et al 2012). Many studies of the chemistry in such regions have been carried out, either through complete spectral surveys of individual sources or by targetting individual molecules in a larger number of sources (see Herbst & van Dishoeck 2009;Caselli & Ceccarelli 2012, for reviews).…”

Deep, Broadband Spectral Line Surveys of Molecule-rich Interstellar Clouds

“…Remijan et al (2004a) reported the detection of CH 3 CN in the 3mm band using BIMA, and the CH 3 CN was further mapped by Hernández-Hernández et al (2014). Other COMs, such as CH 3 OH, 13 CH 3 OH, CH 3 CCH, CH 3 OCH 3 , C 2 H 5 CN, and C 2 H 3 CN, were reported in several millimeter-band line surveys (Hatchell et al 1998b;Fontani et al 2007). …”

“…Both cores have a rich inventory of COMs, revealed by extensive line surveys across the millimeter bands (Helmich et al 1994;Helmich & van Dishoeck 1997;Kalenskii et al 1997Kalenskii et al , 2000aWyrowski et al 1999a;van der Tak et al 2000;Ikeda et al 2001;Alakoz et al 2002;Charnley 2004;Sutton et al 2004;Kim et al 2006;Bisschop et al 2007;Fontani et al 2007;Ratajczak et al 2011;Reiter et al 2011;Li et al 2012;Gerner et al 2014;Hernández-Hernández et al 2014;Ligterink et al 2015;Qin et al 2015). (Helmich & van Dishoeck 1997;Fontani et al 2007;Qin et al 2015), and CH 3 OH has two temperature components (Qin et al 2015).…”