Document Detail

A close halo of large transparent grains around extreme red giant stars.
MedLine Citation:
PMID:  22498626     Owner:  NLM     Status:  In-Data-Review    
An intermediate-mass star ends its life by ejecting the bulk of its envelope in a slow, dense wind. Stellar pulsations are thought to elevate gas to an altitude cool enough for the condensation of dust, which is then accelerated by radiation pressure, entraining the gas and driving the wind. Explaining the amount of mass loss, however, has been a problem because of the difficulty of observing tenuous gas and dust only tens of milliarcseconds from the star. For this reason, there is no consensus on the way sufficient momentum is transferred from the light from the star to the outflow. Here we report spatially resolved, multiwavelength observations of circumstellar dust shells of three stars on the asymptotic giant branch of the Hertzsprung-Russell diagram. When imaged in scattered light, dust shells were found at remarkably small radii (less than about two stellar radii) and with unexpectedly large grains (about 300 nanometres in radius). This proximity to the photosphere argues for dust species that are transparent to the light from the star and, therefore, resistant to sublimation by the intense radiation field. Although transparency usually implies insufficient radiative pressure to drive a wind, the radiation field can accelerate these large grains through photon scattering rather than absorption--a plausible mass loss mechanism for lower-amplitude pulsating stars.
Barnaby R M Norris; Peter G Tuthill; Michael J Ireland; Sylvestre Lacour; Albert A Zijlstra; Foteini Lykou; Thomas M Evans; Paul Stewart; Timothy R Bedding
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Publication Detail:
Type:  Journal Article     Date:  2012-04-11
Journal Detail:
Title:  Nature     Volume:  484     ISSN:  1476-4687     ISO Abbreviation:  Nature     Publication Date:  2012  
Date Detail:
Created Date:  2012-04-13     Completed Date:  -     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  0410462     Medline TA:  Nature     Country:  England    
Other Details:
Languages:  eng     Pagination:  220-2     Citation Subset:  IM    
Sydney Institute for Astronomy, School of Physics, University of Sydney, New South Wales 2006, Australia.
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Comment In:
Nature. 2012;484(7393):172-3   [PMID:  22498620 ]

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