The chemical history of molecules in circumstellar disks - I. Ices

By R. Visser, E. Dishoeck, S. Doty, C. Dullemond. 2009

192 citations recorded by the source corpus.

Context. Many chemical changes occur during the collapse of a molecular cloud to form a low-mass star and the surrounding disk. One-dimensional models have been used so far to analyse these chemical processes, but they cannot properly describe the incorporation of material into disks. Aims. The goal of this work is to understand how material changes chemically as it is transported from the cloud to the star and the disk. Of special interest is the chemical history of the material in the disk at the end of the collapse. Methods. A two-dimensional, semi-analytical model is presented that, for the first time, follows the chemical evolution from the pre-stellar core to the protostar and circumstellar disk. The model computes infall trajectories from any point in the cloud and tracks the radial and vertical motion of material in the viscously evolving disk. It includes a full time-dependent radiative transfer treatment of the dust temperature, which controls much of the chemistry. A small parameter grid is explored to understand the effects of the sound speed and the mass and rotation of the cloud. The freeze-out and evaporation of carbon monoxide (CO) and water (H 2 O), as well as the potential for forming complex organic molecules in ices, are considered as important first steps towards illustrating the full chemistry. Results. Both species freeze out towards the centre before the collapse begins. Pure CO ice evaporates during the infall phase and re-adsorbs in those parts of the disk that cool below the CO desorption temperature of ∼ 18 K. Water remains solid almost everywhere during the infall and disk formation phases and evaporates within ∼10 AU of the star. Mixed CO-H 2 O ices are important in keeping some solid CO above 18 K and in explaining the presence of CO in comets. Material that ends up in the planet- and comet-forming zones of the disk (∼5-30 AU from the star) is predicted to spend enough time in a warm zone (several 104 yr at a dust temperature of 20-40 K) during the collapse to form first-generation complex organic species on the grains. The dynamical timescales in the hot inner envelope (hot core or hot corino) are too short for abundant formation of second-generation molecules by high-temperature gas-phase chemistry.

Subfields: Astronomy and Astrophysics, Organic Chemistry, Physical and Theoretical Chemistry

View Paper: https://www.semanticscholar.org/paper/54a033d96bc9dbd744a3094364de6edb7d5d348f

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Citations in the corpus

The Non-carbonaceous–Carbonaceous Meteorite Dichotomy (2020, background): “Thus, an isotopic heterogeneity within the cloud would have, at least in part, been imparted on the isotopic composition of the disk (Jacquet et al. 2019; Visser et al. 2009).”
Complex organic molecules in protoplanetary disks (2013, background): “Visser et al. (2009) also considered this and concluded that the shock velocities experienced by the gas, ≈ 8 km s−1, are not sufficient to energise ions, such as He+, to energies required for the removal of water molecules from grain surfaces.”
Our astrochemical heritage (2012, background): “Visser et al. (2009, 2011) have been the first to self-consistently follow the chemistry in a twodimensional axisymmetric model of a collapsing (initially) spherical and slowly rotating cloud, on its way toward the formation of a protoplanetary disk.”
Gas- and dust evolution in protoplanetary disks (2010, methodology): “Firstly, as shown by Visser et al.(2009), the geometrical thickness of the disk changes the radial distribution of in-falling matter onto the disk surface, because the finite thickness may “capture” an in-falli g gas parcel before it could reach the midplane.”
THE BURST MODE OF ACCRETION AND DISK FRAGMENTATION IN THE EARLY EMBEDDED STAGES OF STAR FORMATION (2010, unknown): “This is however a reasonable assumption according to Visser et al. (2009), who accurately calculated the gas trajectories in the infalling envelope and found that the bulk of the infalling material landed onto the disk’s outer edge.”
The warm gas atmosphere of the HD 100546 disk seen by Herschel - Evidence of a gas-rich, carbon-poor atmosphere? (2012, methodology): “Freeze-out, thermal, and non-thermal desorption Freeze-out and thermal or non-thermal desorption are implemented following Visser et al. (2009b) and references therein.”
The CO-to-H2 Conversion Factor (2013, background): “For a Draine (1978) interstellar radiation field, R0 = 2.6× 10−10 s−1 (Visser et al. 2009); R0 will vary for radiation fields with other shapes.”
THE SPITZER ICE LEGACY: ICE EVOLUTION FROM CORES TO PROTOSTARS (2011, background): “It is unknown whether cometary ices reformed in the disk or whether they are at least partly pre-solar or protosolar; recent models suggest that much of the original ice will in fact survive accretion from the envelope into the disk (Visser et al. 2009).”
PROSAC: a submillimeter array survey of low-mass protostars - II. The mass evolution of envelopes, disks, and stars from the class 0 through I stages (2009, methodology): “14 compares the temporal evolution of the temperature at a radius of 200 AU between rays through the model with different inclinations with respect to the disk plane in the simulation of Visser et al. (2009).”
Astrochemistry and compositions of planetary systems (2020, background): “Throughout disk formation, infalling material is further subject to irradiation (Visser et al. 2009) and accretion shocks (Neufeld and Hollenbach 1994; Visser and Dullemond 2010; Aota et al.”
Observations of the Icy Universe (2015, background): “Low cometary CO and CO2 may also reflect sublimation of the most volatile, apolar components upon accretion from the envelope to the protoplanetary disk (Visser et al., 2009).”