Physicochemical models: source-tailored or generic?

Abstract

Physicochemical models can be powerful tools to trace the chemical evolution of a protostellar system and allow to constrain its physical conditions at formation. The aim of this work is to assess whether source-tailored modelling is needed to explain the observed molecular abundances around young, low-mass protostars or if, and to what extent, generic models can improve our understanding of the chemistry in the earliest stages of star formation. The physical conditions and the abundances of simple, most abundant molecules based on three models are compared. After establishing the discrepancies between the calculated chemical output, the calculations are redone with the same chemical model for all three sets of physical input parameters. With the differences arising from the chemical models eliminated, the output is compared based on the influence of the physical model. Results suggest that the impact of the chemical model is small compared to the influence of the physical conditions, with considered timescales having the most drastic effect. Source-tailored models may be simpler by design; however, likely do not sufficiently constrain the physical and chemical parameters within the global picture of star-forming regions. Generic models with more comprehensive physics may not provide the optimal match to observations of a particular protostellar system, but allow a source to be studied in perspective of other star-forming regions.

Chemical evolution during the formation of a protoplanetary disk

“…Drozdovskaya et al (2016) found a higher value of 3.7 × 10 −6 at the end of the prestellar phase, when taking into account reaction-diffusion competition. Different physical conditions and timescales during the precollapse phase could also explain the different initial abundances obtained for methanol (Kulterer et al 2020). The total methanol abundance in our model does not evolve significantly during the disk formation and cannot be enhanced as methanol is already formed abundantly in the cold and dense core.…”

Fevering Interstellar Ices Have More CH3OD

“…These core ages are common choices for modelling the prestellar phase in physicochemical models. 40 The boosted abstraction scheme of Model 2B leads to a very high CH 2 DOH/CH 3 OD ratio at 10 K and the youngest considered core age of 10 5 yr (∼ 60 compared to 11 at 3 × 10 5 yr). This indicates that a short, cold, prestellar core stage can lead to a very high CH 2 DOH/CH 3 OD ratio and that this value can be considered an upper limit.…”

“…The physical model is representative of a typical prestellar core. 39,40 The core age of the fiducial model, t core , is assumed to be 3 × 10 5 yr. 40 The dust and gas temperatures (T dust ) are assumed to be the same, and values of 10, 15, 20, 25, and 30 K are considered. The values for the gas density n H = 4 × 10 4 cm −3 and the cosmic ray ionization rate ζ CR = 5 × 10 −17 s −1 remain the same for all discussed modelling runs with the fiducial physical model.…”

“…Here, a short description of the chemical model is given. Details can be found in Walsh [39][40][41][42] and the references therein. The model considers gaseous and solid phases, the latter refers to icy mantles covering the dust grains.…”

“…Interactions between the gas and the ice occur via adsorption, thermal desorption, photodesorption, and CR-induced spot heating. In contrast to the previous work carried out with this model, [39][40][41][42] reactive desorption is not included here. The Langmuir-Hinshelwood mechanism is implemented for the grain-surface chemical reactions.…”