Unexpectedly large mass loss during the thermal pulse cycle of the red giant star R Sculptoris

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Abstract

The asymptotic-giant-branch star R Sculptoris is surrounded by a detached shell of dust and gas1,2. The shell originates from a thermal pulse during which the star underwent a brief period of increased mass loss3,4. It has hitherto been impossible to constrain observationally the timescales and mass-loss properties during and after a thermal pulse—parameters that determine the lifetime of the asymptotic giant branch and the amount of elements returned by the star. Here we report observations of CO emission from the circumstellar envelope and shell around R Sculptoris with an angular resolution of 1.3″. What was previously thought to be only a thin, spherical shell with a clumpy structure is revealed to also contain a spiral structure. Spiral structures associated with circumstellar envelopes have been previously seen, leading to the conclusion that the systems must be binaries5,6,7,8. Combining the observational data with hydrodynamic simulations, we conclude that R Sculptoris is a binary system that underwent a thermal pulse about 1,800 years ago, lasting approximately 200 years. About 3 × 10−3 solar masses of material were ejected at a velocity of 14.3 km s−1 and at a rate around 30 times higher than the pre-pulse mass-loss rate. This shows that about three times more mass was returned to the interstellar medium during and immediately after the pulse than previously thought.

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Figure 1: ALMA Early Science observations of the CO( J = 3 − 2) emission from the asymptotic-giant-branch star R Sculptoris.
Figure 2: The CO( J = 3 − 2) emission at the stellar v LSR of R Sculptoris.
Figure 3: The velocity and mass-loss rate evolution of the stellar wind around R Sculptoris.
Figure 4: LIME radiative transfer model of the circumstellar structure around R Sculptoris.

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Acknowledgements

This paper makes use of ALMA data from project no. ADS/JAO.ALMA#2011.0.00131.S. ALMA is a partnership of ESO (representing its member states), the NSF (USA) and NINS (Japan), together with the NRC (Canada) and NSC and ASIAA (Taiwan), in cooperation with the Republic of Chile. The Joint ALMA Observatory is operated by ESO, AUI/NRAO and NAOJ. We gratefully acknowledge the technical expertise and assistance provided by the Spanish Supercomputing Network (Red Espanola de Supercomputacion), as well as the use of the LaPalma Supercomputer, located at the Instituto de Astrofisica de Canarias. F.K. acknowledges funding by the Austrian Science Fund FWF under project numbers P23586-N16 and I163-N16. C.P. acknowledges funding by the Austrian Science Fund FWF under project number P23006-N16.

Author information

M.M. planned the project, prepared and submitted the proposal, analysed the data, and wrote the manuscript. S.M. was involved in project preparation, data interpretation, did the SPH modelling, and commented on the manuscript. W.V. was involved in project planning, proposal preparation, data reduction and analysis, radiative transfer modelling, and commented on the manuscript. S.R. was involved in project planning, data analysis, and commented on the manuscript. The remaining authors were involved in the project preparation, science discussion, and commented on the manuscript.

Correspondence to M. Maercker.

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The authors declare no competing financial interests.

Supplementary information

Supplementary information

This file contains Supplementary Notes 1-4, Supplementary Figure 1, the full legend for Supplementary Video 1 and Supplementary References. (PDF 239 kb)

Animation of the SPH model of the evolution of the CSE around R Sculptoris over 2,200 years

In the animation we model a binary system with a primary mass of 1.6 M, a companion mass of 0.25 M, and a separation of 60 AU. The shaping of the wind into a spiral structure is clearly visible. At t = 0 years the AGB star undergoes a thermal pulse, forming an expanding detached shell. The post-pulse mass-loss continues to form a spiral, connecting the detached shell with the central star. At t ≈ 2,000 years the system has formed a detached shell and spiral structure as observed in the ALMA observations. See Supplementary Information PDF for full video legend. (MOV 7515 kb)

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Maercker, M., Mohamed, S., Vlemmings, W. et al. Unexpectedly large mass loss during the thermal pulse cycle of the red giant star R Sculptoris. Nature 490, 232–234 (2012) doi:10.1038/nature11511

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