The Role of Ultraviolet Photons in Circumstellar Astrochemistry

Abstract

Stars with masses between 1 and 8 solar masses (M${}_{\odot }$) lose large amounts of material in the form of gas and dust in the late stages of stellar evolution, during their Asymptotic Giant Branch phase. Such stars supply up to 35% of the dust in the interstellar medium and thus contribute to the material out of which our solar system formed. In addition, the circumstellar envelopes of these stars are sites of complex, organic chemistry with over 80 molecules detected in them. We show that internal ultraviolet photons, either emitted by the star itself or from a close-in, orbiting companion, can significantly alter the chemistry that occurs in the envelopes particularly if the envelope is clumpy in nature. At least for the cases explored here, we find that the presence of a stellar companion, such as a white dwarf star, the high flux of UV photons destroys H${}_2$O in the inner regions of carbon-rich AGB stars to levels below those observed and produces species such as C${}^{+}$ deep in the envelope in contrast to the expectations of traditional descriptions of circumstellar chemistry.

arXiv commentTo be published in Chinese Journal of Chemical Physics

References in corpus (34)

• The UMIST database for astrochemistry 2012
• Photodissociation and photoionisation of atoms and molecules of astrophysical interest
• Dust formation in the oxygen-rich AGB star IK Tau
• Unexpectedly large mass loss during the thermal pulse cycle of the red giant R Sculptoris!
• `Thermal' SiO radio line emission towards M-type AGB stars: a probe of circumstellar dust formation and dynamics
• Imaging the circumstellar envelopes of AGB stars
• Molecular abundances in the inner layers of IRC +10216
• (Sub)stellar companions shape the winds of evolved stars
• The inner wind of IRC+10216 revisited: New exotic chemistry and diagnostic for dust condensation in carbon stars
• Density-enhanced gas and dust shells in a new chemical model for IRC+10216
• Warm water vapour in the sooty outflow from a luminous carbon star
• Chemical equilibrium in AGB atmospheres: Successes, failures, and prospects for small molecules, clusters, and condensates
• Mass Transfer and Disc Formation in AGB Binary Systems
• Discovery of SiCSi in IRC+10216: A missing link between gas and dust carriers of SiC bonds
• A high resolution line survey of IRC+10216 with Herschel. First results: Detection of warm silicon dicarbide SiC2
• Photochemistry in the inner layers of clumpy circumstellar envelopes: formation of water in C-rich objects and of C-bearing molecules in O-rich objects
• ALMA observations of the nearby AGB star L2 Puppis - I. Mass of the central star and detection of a candidate planet
• A Catalog of GALEX Ultraviolet Emission from Asymptotic Giant Branch Stars
• Water in IRC+10216: a genuine formation process by shock-induced chemistry in the inner wind
• Determining the effects of clumping and porosity on the chemistry in a non-uniform AGB outflow
• Wind morphology around cool evolved stars in binaries: the case of slowly accelerating oxygen-rich outflows
• An edge-on translucent dust disk around the nearest AGB star L2 Puppis - VLT/NACO spectro-imaging from 1.04 to 4.05 microns and VLTI interferometry
• Photodissociation and chemistry of N${}_2$ in the circumstellar envelope of carbon-rich AGB stars
• Nucleation of small silicon carbide dust clusters in AGB stars
• Silicon in the dust formation zone of IRC +10216 as observed with PACS and SPIRE on board Herschel
• Developing a self-consistent AGB wind model: II. Non-classical, non-equilibrium polymer nucleation in a chemical mixture
• A New Method of Determining the Characteristics of Evolved Binary Systems Revealed in the Observed Circumstellar Patterns: Application to AFGL 3068
• Ultraviolet emission from main-sequence companions of AGB stars
• Photodissociation of CO in the outflow of evolved stars
• Detection of OH Towards the Extreme Carbon Star IRC+10216
• The peculiar distribution of CH3CN in IRC+10216 seen by ALMA
• The Role of Internal Photons on the Chemistry of the Circumstellar Envelopes of AGB Stars
• Dust-gas chemistry in AGB outflows: Chemical modelling of dust-gas chemistry within AGB outflows I. Effect on the gas-phase chemistry
• Chemical modelling of dust-gas chemistry within AGB outflows -- II. Effect of the dust-grain size distribution

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