English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Tools annual

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools monthly

Global: Zendy Plus monthly

Presents the access of premium content as premium feature

Premium Content

Global: Zendy Plus annual

Global: Zendy Free Plan

Chemical equilibrium has proven extremely useful to predict the chemicalcomposition of AGB atmospheres. Here we use a recently developed code and anupdated thermochemical database, including gaseous and condensed speciesinvolving 34 elements, to compute the chemical equilibrium composition of AGBatmospheres of M-, S-, and C-type stars. We include for the first time TixCyclusters, with x = 1-4 and y = 1-4, and selected larger clusters ranging up toTi13C22, for which thermochemical data is obtained from quantum chemicalcalculations. We find that in general chemical equilibrium reproduces well theobserved abundances of parent molecules in circumstellar envelopes of AGBstars. There are however severe discrepancies, of various orders of magnitude,for some parent molecules: HCN, CS, NH3, and SO2 in M-type stars, H2O and NH3in S-type stars, and the hydrides H2O, NH3, SiH4, and PH3 in C-type stars.Several molecules not yet observed in AGB atmospheres, like SiC5, SiNH, SiCl,PS, HBO, and the metal-containing molecules MgS, CaS, CaOH, CaCl, CaF, ScO,ZrO, VO, FeS, CoH, and NiS, are good candidates for detection withobservatories like ALMA. The first condensates predicted are carbon, TiC, andSiC in C-rich atmospheres and Al2O3 in O-rich outflows. The most probablegas-phase precursors of dust are acetylene, atomic carbon, and/or C3 for carbondust, SiC2 and Si2C for SiC dust, and atomic Al and AlOH, AlO, and Al2O forAl2O3 dust. In the case of TiC dust, atomic Ti is probably the main supplier oftitanium. However, chemical equilibrium predicts that clusters like Ti8C12 andTi13C22 become the major reservoirs of titanium at the expense of atomic Ti inthe region where condensation of TiC is expected to occur, suggesting that theassembly of large TixCy clusters could be related to the formation of the firstcondensation nuclei of TiC.

Chemical equilibrium in AGB atmospheres: Successes, failures, and prospects for small molecules, clusters, and condensates