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Post Info TOPIC: R Sculptoris
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Title: A detailed view of the gas shell around R Sculptoris with ALMA
Author: M. Maercker, W.H.T. Vlemmings, M. Brunner, E. De Beck, E.M. Humphreys, F. Kerschbaum, M. Lindqvist, H. Olofsson, S. Ramstedt

Thermal pulses are fundamental to the chemical evolution of AGB stars and their circumstellar envelopes. A further consequence of thermal pulses is the formation of detached shells of gas and dust around the star. We aim to determine the physical properties of the detached gas shell around R Sculptoris, in particular the shell mass and temperature, and to constrain the evolution of the mass-loss rate during and after a thermal pulse. We analyse CO(1-0), CO(2-1), and CO(3-2) emission, observed by. The spatial resolution of the ALMA data allows us to separate the detached shell emission from the extended emission inside the shell. We perform radiative transfer modelling of both components to determine the shell properties and the post-pulse mass-loss properties. The ALMA data show a gas shell with a radius of 19.5" expanding at 14.3km/s. The different scales probed by the ALMA Cycle 0 array show that the shell must be entirely filled with gas, contrary to the idea of a detached shell. The comparison to single-dish spectra and radiative transfer modelling confirms this. We derive a shell mass of 4.5e-3 Msun with a temperature of 50K. Typical timescales for thermal pulses imply a pulse mass-loss rate of 2.3e-5 Msun/yr. For the post-pulse mass-loss rate, we find evidence for a gradual decline of the mass-loss rate, with an average value of 1.6e-5 Msun/yr. The total amount of mass lost since the last thermal pulse is 0.03 Msun, a factor four higher compared to classical models, with a sharp decline in mass-loss rate immediately after the pulse. We find that the mass-loss rate after a thermal pulse has to decline more slowly than generally expected from models of thermal pulses. This may cause the star to lose significantly more mass during a thermal pulse cycle, which affects the chemical evolution of the star and the interstellar medium.

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Blobrana


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Title: Unexpectedly large mass loss during the thermal pulse cycle of the red giant R Sculptoris!
Authors: M. Maercker, S. Mohamed, W. H. T. Vlemmings, S. Ramstedt, M. A. T. Groenewegen, E. Humphreys, F. Kerschbaum, M. Lindqvist, H. Olofsson, C. Paladini, M. Wittkowski, I. de Gregorio-Monsalvo, L.-A. Nyman

The asymptotic giant branch star R Sculptoris is surrounded by a detached shell of dust and gas. The shell originates from a thermal pulse during which the star undergoes a brief period of increased mass loss. 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 on 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 arcsec. What was hitherto thought to be only a thin, spherical shell with a clumpy structure, is revealed to contain a spiral structure. Spiral structures associated with circumstellar envelopes have been seen previously, from which it was concluded that the systems must be binaries. Using the data, combined with hydrodynamic simulations, we conclude that R Sculptoris is a binary system that underwent a thermal pulse approximately 1800 years ago, lasting approximately 200 years. About 0.003 solar masses of mass was ejected at a velocity of 14.3 km s-1 and at a rate approximately 30 times higher than the prepulse mass-loss rate. This shows that approximately 3 times more mass is returned to the interstellar medium during and immediately after a pulse than previously thought.

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Blobrana


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Surprising Spiral Structure Spotted by ALMA

eso1239a.jpg

Astronomers using the Atacama Large Millimetre/submillimetre Array (ALMA) have discovered a totally unexpected spiral structure in the material around the old star R Sculptoris. This is the first time that such a structure, along with an outer spherical shell, has been found around a red giant star. It is also the first time that astronomers could get full three-dimensional information about such a spiral. The strange shape was probably created by a hidden companion star orbiting the red giant. This work is one of the first ALMA early science results to be published and it appears in the journal Nature this week. 
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