Chemical significance of different temperature regimes for cosmic-ray-induced heating of whole interstellar grains. (arXiv:1904.11368v1 [astro-ph.GA])
<a href="http://arxiv.org/find/astro-ph/1/au:+Kalvans_J/0/1/0/all/0/1">Juris Kalvans</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Kalnin_J/0/1/0/all/0/1">Juris Roberts Kalnin</a>
Cosmic-ray-induced whole-grain heating induces evaporation and other
processes that affect the chemistry of interstellar clouds. With recent data on
grain heating frequencies as an input for a modified rate-equation
astrochemical model, this study examines, which whole-grain heating temperature
regime is the most efficient at altering the chemical composition of gas and
ices. Such a question arises because low-temperature heating, albeit less
effective at inducing evaporation of adsorbed species, happens much more often
than high-temperature grain heating. The model considers a delayed
gravitational collapse of a Bonnor-Ebert sphere, followed by a quiescent cloud
core stage. It was found that the whole-grain heating regimes can be divided in
three classes, depending on their induced physico-chemical effects. Heating to
low-temperature thresholds of 27 and 30 K induce desorption of the most
volatile of species – N2 and O2 ices, and adsorbed atoms. The
medium-temperature thresholds 40, 50, and 60 K allow effective evaporation of
CO and CH4, delaying their accumulation in ices. We find that the 40 K
threshold is the most effective cosmic-ray induced whole-grain heating regime
because its induced evaporation of CO promotes major abundance changes also for
other compounds. An important role in grain cooling may be played by molecular
nitrogen as the most volatile of the abundant species in the icy mantles.
Whole-grain heating determines the sequence of accretion for different
molecules on to grain surface, which plays a key role in the synthesis of
complex organic molecules.
Cosmic-ray-induced whole-grain heating induces evaporation and other
processes that affect the chemistry of interstellar clouds. With recent data on
grain heating frequencies as an input for a modified rate-equation
astrochemical model, this study examines, which whole-grain heating temperature
regime is the most efficient at altering the chemical composition of gas and
ices. Such a question arises because low-temperature heating, albeit less
effective at inducing evaporation of adsorbed species, happens much more often
than high-temperature grain heating. The model considers a delayed
gravitational collapse of a Bonnor-Ebert sphere, followed by a quiescent cloud
core stage. It was found that the whole-grain heating regimes can be divided in
three classes, depending on their induced physico-chemical effects. Heating to
low-temperature thresholds of 27 and 30 K induce desorption of the most
volatile of species – N2 and O2 ices, and adsorbed atoms. The
medium-temperature thresholds 40, 50, and 60 K allow effective evaporation of
CO and CH4, delaying their accumulation in ices. We find that the 40 K
threshold is the most effective cosmic-ray induced whole-grain heating regime
because its induced evaporation of CO promotes major abundance changes also for
other compounds. An important role in grain cooling may be played by molecular
nitrogen as the most volatile of the abundant species in the icy mantles.
Whole-grain heating determines the sequence of accretion for different
molecules on to grain surface, which plays a key role in the synthesis of
complex organic molecules.
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