Evaporation of ices near massive stars: models based on laboratory temperature programmed desorption data

Abstract

Hot cores and their precursors contain an integrated record of the physics of the collapse process in the chemistry of the ices deposited during that collapse. In this paper, we present results from a new model of the chemistry near high‐mass stars in which the desorption of each species in the ice mixture is described as indicated by new experimental results obtained under conditions similar to those in hot cores. Our models show that provided there is a monotonic increase in the temperature of the gas and dust surrounding the protostar, the changes in the chemical evolution of each species due to differential desorption are important. The species H2S, SO, SO2, OCS, H2CS, CS, NS, CH3OH, HCOOCH3, CH2CO, C2H5OH show a strong time dependence that may be a useful signature of time evolution in the warm‐up phase as the star moves on to the main sequence. This preliminary study demonstrates the consequences of incorporating reliable temperature programmed desorption data into chemical models.

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

“…At ≈ 10 4.5 years the sudden jump in abundance of methyl formate and ethyl cyanide is due to the evaporation of these species from the grain mantle surface. At late times varying the final mass of the star does not seem to affect the fractional abundances of the complex species we consider; however, as expected (see Viti et al 2004), a higher mass implies an earlier icy mantle evaporation. In general a very low abundance of COMs implies a young age with the exception of methyl cyanide (but see Sect.…”

“…Results of chemical models in the past have suggested that determining abundance ratios of typical hot core tracers (e.g. CH3CN) as well as sulphur-bearing species could serve as indicators of both mass and age (Hatchell et al 1998;Viti et al 2001;Buckle & Fuller 2003;Viti et al 2004). However much care has to be taken due to the fact that most species do not necessarily trace the very inner part of the core and their emission region probably spans a range of densities and temperatures that make the interpretation difficult (Wakelam et al 2004).…”

“…Some coefficients have been updated with those from the KIDA database (Wakelam et al 2009). Our database also includes some simple grain-surface reactions (mainly hydrogenation) as in Viti et al (2004) as well as selected routes for grain-surface formation of glycolaldehyde as in Woods et al (2012) and methyl formate as in Occhiogrosso et al (2011). In Phase I non-thermal desorption is considered as in Roberts et al (2007).…”

“…UCL CHEM treatment of the temperature and of the ice sublimation is as in , where details of how the temperature increases with time leading to the subsequent time dependent sublimation of the ice mantles can be found. Initial atomic abundances are taken from Sofia & Meyer (2001), as in Viti et al (2004). For the gas-phase chemistry, reaction rate coefficients are taken from the UMIST database (Woodall et al 2007).…”

Deuterium chemistry of dense gas in the vicinity of low-mass and massive star-forming regions

“…The present model, UCL DCHEM, is an adaptation of the UCL CHEM model (Viti & Williams 1999;Viti et al 2004), which in its original form did not include a deuterium network. 2 This paper is organized as follows: in §2 we describe our model; in §3 we present the results of the grid of models we ran.…”