文章基本信息

标题：Beaming in on some stimulating issues in stellar evolution
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作者：A.M.S. Richards
期刊名称：PoS - Proceedings of Science
印刷版ISSN：1824-8039
出版年度：2006
出版社：SISSA, Scuola Internazionale Superiore di Studi Avanzati
摘要：This review discusses some recent maser observations and their interpretation, with the emphasis on physical processes in star formation and mass loss from evolved stars. I draw attention to issues where high-resolution observations have led to new, surprising or controversial developments. I also mention some results and prospects for maser studies arising from new instruments and surveys. Highlights include measurements of Zeeman splitting in non-paramagnetic species such as water and methanol. The water maser results often indicate a much stronger magnetic field than is seen by nearby OH masers, suggesting that the former arise from overdense clumps. Maser scattering or Faraday rotation implicates a significant ionised fraction. The increasing number of axisymmetric outflows from evolved stars, often with no signs of rotation, are likely to be shaped by magnetic fields, but there is no agreement on their origin. Extraordinary thousand-AU filaments have been seen in e.g. W3(OH) in OH and methanol, and in S128 in water. At the other extreme, compact 6-GHz OH and methanol are associated on sub-arcsec, but not milli-arcsec scales; does this indicate chemical chronology or competitive maser amplification? Another surprise is the increasing number of weak methanol and water masers associated with low-mass young stellar objects. Masers are still an ideal tool to probe the chemistry, kinematics, density, magnetic field and ionised fraction, and hence the rate and clumping scales of star formation – but the process is intrinsically a lot more complex than it once seemed.