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标题：The Evolving Radio Photospheres of Long-period Variable Stars
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作者：L. D. Matthews ; M. J. Reid ; K. M. Menten 等
期刊名称：The Astronomical journal
印刷版ISSN：0004-6256
电子版ISSN：1538-3881
出版年度：2018
卷号：156
期号：1
页码：1-15
DOI：10.3847/1538-3881/aac491
语种：English
出版社：American Institute of Physics
摘要：Observations with the Karl G. Jansky Very Large Array at 46GHz (λ≈7mm) have been used to measure the size and shape of the radio photospheres of four long-period variable stars: RLeonis (R Leo), IRC+10216 (CW Leonis), χCygni (χ Cyg), and WHydrae (WHya). The shapes of the stars range from nearly round to ellipticities of ∼0.15. Comparisons with observations taken several years earlier show that the photospheric parameters (mean diameter, shape, and/or flux density) of each of the stars have changed over time. Evidence for brightness asymmetries and nonuniformities across the radio surfaces is also seen in the visibility domain and in images obtained using a sparse-modeling image reconstruction technique. These trends may be explained as manifestations of large-scale irregular convective flows on the stellar surface, although effects from nonradial pulsations cannot be excluded. Our data also allow a new evaluation of the proper motion of IRC+10216. Our measurement is in agreement with previous values obtained from radio-wavelength measurements, and we find no evidence of statistically significant astrometric perturbations from a binary companion.
关键词：stars: AGB and post-AGB;stars: atmospheres;stars: fundamental parameters;stars: imaging