Chemistry in disks

Abstract

Context. We describe and benchmark two sophisticated chemical models developed by the Heidelberg and Bordeaux astrochemistry groups. Aims. The main goal of this study is to elaborate on a few well-described tests for state-of-the-art astrochemical codes covering a range of physical conditions and chemical processes, in particular those aimed at constraining current and future interferometric observations of protoplanetary disks. Methods. We considered three physical models: a cold molecular cloud core, a hot core, and an outer region of a T Tauri disk. Our chemical network (for both models) is based on the original gas-phase osu_03_2008 ratefile and includes gas-grain interactions and a set of surface reactions for the H-, O-, C-, S-, and N-bearing molecules. The benchmarking was performed with the increasing complexity of the considered processes: (1) the pure gas-phase chemistry, (2) the gas-phase chemistry with accretion and desorption, and (3) the full gas-grain model with surface reactions. The chemical evolution is modeled within 10 9 years using atomic initial abundances with heavily depleted metals and hydrogen in its molecular form. Results. The time-dependent abundances calculated with the two chemical models are essentially the same for all considered physical cases and for all species, including the most complex polyatomic ions and organic molecules. This result, however, required a lot of effort to make all necessary details consistent through the model runs, e.g., definition of the gas particle density, density of grain surface sites, or the strength and shape of the UV radiation field. Conclusions. The reference models and the benchmark setup, along with the two chemical codes and resulting time-dependent abundances are made publicly available on the internet. This will facilitate and ease the development of other astrochemical models and provide nonspecialists with a detailed description of the model ingredients and requirements to analyze the cosmic chemistry as studied, e.g., by (sub-) millimeter observations of molecular lines.

The interstellar gas-phase chemistry of HCN and HNC

“…The new chemical reactions for HCN and HNC formation and destruction listed in Table 2 have been applied to the chemical model Nautilus (Hersant et al 2009, Semenov et al 2010. The version of Nautilus used for this work is the same as the one used by Loison et al (2013) and we refer to this paper for a complete description of the model.…”

Chemical modeling of the L1498 and L1517B prestellar cores: CO and HCO+depletion

“…In our first models, we neglect the desorption from secondary UV photons, but their effect is also investigated later in the paper. Finally, we also consider electron attachment on grains, as well as recombination of ions onto charged grains, following Semenov et al (2010).…”

Tracing the evolutionary stage of Bok globules: CCS and NH3

“…We used the recent chemical network including a variety of grain surface reactions described in Semenov et al (2010) along with a simplified physical model. The representative physical parameters of each group were taken from the globule study of L2010, i.e.…”