The impact of stellar companion UV photons on the chemistry of the circumstellar environments of AGB stars

Abstract

Spherical asymmetries are prevalent within the outflows of AGB stars. Since binary interaction with a stellar or planetary companion is thought to be the underlying mechanism behind large-scale structures, we included the effects of UV radiation originating from a stellar companion in our chemical kinetics model. The one-dimensional model provides a first approximation of its effects on the chemistry throughout the outflow. The presence of a close-by stellar companion can strongly influence the chemistry within the entire outflow. Its impact depends on the intensity of the radiation (set by the stellar radius and blackbody temperature) and on the extinction the UV radiation experiences (set by the outflow density, density structure, and assumed radius of dust formation). Parent species can be photodissociated by the companion, initiating a rich photon-driven chemistry in the inner parts of the outflow. The outcome depends on the balance between two-body reactions and photoreactions. If two-body reactions dominate, chemical complexity within the outflow increases. This can make the abundance profiles of daughters appear like those of parents, with a larger inner abundance and a gaussian decline. If photoreactions dominate, the outflow can appear molecule-poor. We model three stellar companions. The impact of a red dwarf companion is limited. Solar-like companions show the largest effect, followed by a white dwarf. A stellar companion can also lead to the formation of unexpected species. The outflow's molecular content, especially combined with abundance profiles, can indicate a stellar companion's presence. Our results pave the way for further outflow-specific (three-dimensional) model development.

arXiv commentAccepted for publication in the Monthly Notices of the Royal Astronomical Society. Main paper: 20 pages, 12 figures, 4 tables. Supplementary material: 42 pages, 66 figures, 2 tables. Revision: corrections to legibility of the label of Fig. A2

References in corpus (51)

• Mind your Ps and Qs: the Interrelation between Period (P) and Mass-ratio (Q) Distributions of Binary Stars
• The UMIST database for astrochemistry 2012
• Photodissociation and photoionisation of atoms and molecules of astrophysical interest
• The Origin and Shaping of Planetary Nebulae: Putting the Binary Hypothesis to the Test
• Evidence for the White Dwarf Nature of Mira B
• Dust formation in the oxygen-rich AGB star IK Tau
• The role of binaries in the enrichment of the early Galactic halo. III. Carbon-enhanced metal-poor stars -- CEMP-s stars
• Imaging the circumstellar envelopes of AGB stars
• (Sub)stellar companions shape the winds of evolved stars
• Orbital properties of binary post-AGB stars
• 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
• The abundance of HCN in circumstellar envelopes of AGB stars of different chemical types
• ALMA data suggest the presence of a spiral structure in the inner wind of CW Leo
• The growth of carbon chains in IRC+10216 mapped with ALMA
• Study of the inner dust envelope and stellar photosphere of the AGB star R Doradus using SPHERE/ZIMPOL
• The millimeter IRAM-30m line survey toward IK Tau
• 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
• The circumstellar envelope of IRC+10216 from milli-arcsecond to arcmin scales
• The wonderful complexity of the Mira AB system
• Evolution and Mass Loss of Cool Ageing Stars: a Daedalean Story
• ALMA spectral line and imaging survey of a low and a high mass-loss rate AGB star between 335 and 362 GHz
• Sulphur molecules in the circumstellar envelopes of M-type AGB stars
• Binarity in Cool Asymptotic Giant Branch Stars: A Galex Search for Ultraviolet Excesse
• A HIFI view on circumstellar H2O in M-type AGB stars: radiative transfer, velocity profiles, and H2O line cooling
• An independent distance estimate to CW Leo
• A Catalog of GALEX Ultraviolet Emission from Asymptotic Giant Branch Stars
• Wide Binary Effects on Asymmetries in Asymptotic Giant Branch Circumstellar Envelopes
• Chemical content of the circumstellar envelope of the oxygen-rich AGB star R Dor: Non-LTE abundance analysis of CO, SiO, and HCN
• The widespread occurence of water vapor in the circumstellar envelopes of carbon-rich AGB stars: first results from a survey with Herschel/HIFI
• Determining the effects of clumping and porosity on the chemistry in a non-uniform AGB outflow
• 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
• Wind morphology around cool evolved stars in binaries: the case of slowly accelerating oxygen-rich outflows
• Symbiotic stars: Observations confront theory
• Sulphur-bearing molecules in AGB stars I: The occurrence of hydrogen sulfide
• Atomic Carbon in the Envelopes of Carbon-Rich Post-AGB Stars
• Circumstellar molecular composition of the oxygen-rich AGB star IK Tau: I. Observations and LTE chemical abundance analysis
• SPH modelling of companion-perturbed AGB outflows including a new morphology classification scheme
• ALMA detection of a tentative nearly edge-on rotating disk around the nearby AGB star R~Doradus
• 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
• An ALMA view of SO and SO${}_2$ around oxygen-rich AGB stars
• SPH modelling of wind-companion interactions in eccentric AGB binary systems
• Circumstellar ammonia in oxygen-rich evolved stars
• Constraints on the H2O formation mechanism in the wind of carbon-rich AGB stars
• Strong Variable Ultraviolet Emission from Y Gem: Accretion Activity in an AGB Star with a Binary Companion?
• Structure and dynamics of the inner nebula around the symbiotic stellar system R Aqr
• The surprisingly carbon-rich environment of the S-type star W Aql
• Detection of CI line emission towards the oxygen-rich AGB star omi Cet
• Detection of CI line emission from the detached CO shell of the AGB star R Sculptoris

Cited by in corpus (13)

• ATOMIUM: Probing the inner wind of evolved O-rich stars with new, highly excited H${}_2$O and OH lines
• Investigating Anomalous Photochemistry in the Inner Wind of IRC+10216 Through Interferometric Observations of HC${}_3$N
• First detection of AlF line emission towards M-type AGB stars
• The unusual 3D distribution of NaCl around the AGB star IK Tau
• Charting Circumstellar Chemistry of Carbon-rich AGB Stars: I. ALMA 3 mm spectral surveys
• An accreting dwarf star orbiting the S-type giant star pi1 Gru
• ATOMIUM: Continuum emission and evidence of dust enhancement from binary motion
• Sensitivity study of chemistry in AGB outflows using chemical kinetics
• Disentangling physics and chemistry in AGB outflows: revealing degeneracies when adding complexity
• High-angular-resolution ALMA imaging of the inhomogeneous dynamical atmosphere of the asymptotic giant branch star W Hya
• Charting circumstellar chemistry of carbon-rich asymptotic giant branch stars. II. Abundances and spatial distributions of CS
• Exploring circumstellar chemistry in X-ray emitting AGB stars
• The dusty envelopes of asymptotic giant branch stars with ultraviolet excesses