Molecular shells in IRC+10216: tracing the mass loss history

Abstract

The ejecta of thermally-pulsating AGB stars largely control the chemical evolution of galaxies. Yet, both, the mass-loss process and the gas chemical composition remain poorly understood. We present maps of the extended 12CO and 13CO emission in IRC+10216, the envelope of CW Leo, the high mass loss star the closest to the Sun. IRC+10216 is nearly spherical and expands radially with a velocity of 14.5 km/s. The observations, made with the IRAM 30-m telescope, have a sensibility, calibration, and angular resolution far higher than previous studies. The angular resolution is 11", which corresponds to an expansion time of 500 yr. The CO emission consists of a centrally peaked pedestal and a series of bright, nearly spherical shells. It peaks on CW Leo and remains relatively strong up to 180". Further out it becomes very weak and vanishes as CO gets photodissociated. The CO maps allow to trace the mass loss history in the last 8000 yr. The bright CO shells denote overdense regions, which indicate that the mass loss process is highly variable on timescales of hundreds of years. The new data, however, infirm previous claims of a strong decrease of the average mass loss in the last few thousand years. The overdense shells are not perfectly concentric and extend farther to the N-NW. The typical shell separation is 800-1000 yr in the middle of the envelope, but seems to increase outwards. The shell-intershell brightness contrast is $\ge$ 3. All those key features can be accounted for if CW Leo has a companion star with a period of $\sim$ 800 yr that increases the mass loss rate when it comes close to periastron. Higher angular resolution observations are needed to fully resolve the dense shells and measure the density contrast. The latter plays an essential role for our understanding of the envelope chemistry.

Accepted for publication in A&A. Text edited with respect to previous version

References in corpus (29)

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• Detection of C5N- and vibrationally excited C6H in IRC +10216
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• ALMA data suggest the presence of a spiral structure in the inner wind of CW Leo
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• Laboratory and Astronomical Discovery of HydroMagnesium Isocyanide
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• The circumstellar envelope of IRC+10216 from milli-arcsecond to arcmin scales
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• Solar-Like Cycle in Asymptotic Giant Branch Stars
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• Discovery of multiple dust shells beyond 1 arcmin in the circumstellar envelope of IRC+10216 using Herschel/PACS
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• Wide Binary Effects on Asymmetries in Asymptotic Giant Branch Circumstellar Envelopes
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• Molecular shells in IRC+10216: Evidence for non-isotropic and episodic mass loss enhancement
• Maps of the Molecular Emission Around 18 Evolved Stars
• Detection of OH Towards the Extreme Carbon Star IRC+10216
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Cited by in corpus (59)

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• Aperture synthesis imaging of the carbon AGB star R Sculptoris: Detection of a complex structure and a dominating spot on the stellar disk
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• ATOMIUM: ALMA tracing the origins of molecules in dust forming oxygen rich M-type stars: Motivation, sample, calibration, and initial results
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• The peculiar distribution of CH3CN in IRC+10216 seen by ALMA
• The abundance of C2H4 in the circumstellar envelope of IRC+10216
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• Monitor variability of millimeter lines in IRC +10216
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• The maser emitting structure and time variability of the SiS lines J=14-13 and 15-14 in IRC+10216
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• DEATHSTAR: Nearby AGB stars with the Atacama Compact Array II. CO envelope sizes and asymmetries: The S-type stars
• Clues to NaCN formation
• Radiation-pressure-driven sub-Keplerian rotation of the disc around the AGB star L2 Pup
• Chemistry in AGB stars: successes and challenges
• Charting Circumstellar Chemistry of Carbon-rich AGB Stars: I. ALMA 3 mm spectral surveys
• Multi-frequency high spectral resolution observations of HCN toward the circumstellar envelope of Y CVn
• How to disentangle geometry and mass-loss rate from AGB-star spectral energy distributions -- The case of EP Aqr
• Non-Zeeman Circular Polarization of Molecular Spectral Lines in the ISM
• ATOMIUM: Continuum emission and evidence of dust enhancement from binary motion
• Detection of the S(1) Rotational Line of H2 toward IRC+10216: A Simultaneous Measurement of Mass-Loss Rate and CO Abundance
• Multi-epoch Optical Images of IRC+10216 Tell About the Central Star And the Adjacent Environment
• Multi-line study of the radial extent of SiO, CS, and SiS in AGB envelopes
• Warm CO in evolved stars from the THROES catalogue. II. Herschel/PACS spectroscopy of C-rich envelopes
• Ionized carbon around IRC +10216
• The Sub-mm Variability of IRC+10216 and $o$ Ceti
• Evidence for orbital motion of CW Leonis from ground-based astrometry
• Rings and arcs around evolved stars -- III. Physical conditions of the ring-like structures in the planetary nebula IC 4406 revealed by MUSE
• Probing the dynamical and kinematical structures of detached shells around AGB stars
• Interrelations between Astrochemistry and Galactic Dynamics
• [C I] and [C II] emission in the circumstellar envelope of IRC +10216 I. Observational data and NLTE modeling of the [C I] emission
• Measurement of the Electric Dipole Moment of AlCl by Stark Level Spectroscopy
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• Near-infrared Integral-field Spectroscopy of the Wind Forming Region of CW Leo