Probing the dynamical and kinematical structures of detached shells around AGB stars

Abstract

Aims. We aim to resolve the spatial and kinematic sub-structures in five detached-shell sources to provide detailed constraints for hydrodynamic models that describe the formation and evolution of the shells. Methods. We use observations of the 12 CO (1-0) emission towards five carbon-AGB stars with ALMA. The data have angular resolutions of 0.3 arcsec to 1arcsec and a velocity resolution of 0.3 km/s . This enables us to quantify spatial and kinematic structures in the shells. Results. The observed emission is separated into two distinct components: a more coherent, bright outer shell and a more filamentary, fainter inner shell. The kinematic information shows that the inner sub-shells move at a higher velocity relative to the outer sub-shells. The observed sub-structures confirm the predictions from hydrodynamical models. However, the models do not predict a double-shell structure, and the CO emission likely only traces the inner and outer edges of the shell, implying a lack of CO in the middle layers of the detached shell. Previous estimates of the masses and temperatures are consistent with originating mainly from the brighter subshell, but the total shell masses are likely lower limits. Conclusions. The observed spatial and kinematical splittings of the shells appear consistent with results from hydrodynamical models, provided the CO emission does not trace the H2 density distribution in the shell but rather traces the edges of the shells. It is therefore not possible to constrain the total shell mass based on the CO observations alone. Complementary observations of, e.g., CI as a dissociation product of CO would be necessary to understand the distribution of CO compared to H2.

18 pages (incl. 5 pages Appendix), 13 Figures

References in corpus (18)

• CASA, the Common Astronomy Software Applications for Radio Astronomy
• Updated stellar yields from Asymptotic Giant Branch models
• The Dawes Review 2: Nucleosynthesis and stellar yields of low and intermediate-mass single stars
• Stellar Models and Yields of Asymptotic Giant Branch Stars
• Unexpectedly large mass loss during the thermal pulse cycle of the red giant R Sculptoris!
• (Sub)stellar companions shape the winds of evolved stars
• Molecular shells in IRC+10216: tracing the mass loss history
• Properties of detached shells around carbon stars: Evidence of interacting winds
• Mass Loss Evolution and the Formation of Detached Shells around TP-AGB Stars
• High-resolution HST/ACS images of detached shells around carbon stars
• Imaging the circumstellar dust around AGB stars with PolCor
• The detached dust and gas shells around the carbon star U Ant
• Photodissociation of CO in the outflow of evolved stars
• A detailed view of the gas shell around R Sculptoris with ALMA
• Rings and filaments: The remarkable detached CO shell of U Antliae
• The detached dust shells around the carbon AGB stars R Scl and V644 Sco
• Dust in AGB wind-ISM interaction regions
• Detection of CI line emission from the detached CO shell of the AGB star R Sculptoris

Cited by in corpus (2)

• Impact of a binary companion in AGB outflows on CO spectral lines
• Exploring circumstellar chemistry in X-ray emitting AGB stars