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Measuring the Distance of VX Sagittarii with SiO Maser Proper Motions, Chen, Xi; Shen, Zhi-Qiang; Xu, Ye, Chinese Journal of Astronomy & Astrophysics154, #7 (August 2007), pp. 531–538, Bibcode: 2007ChJAA...7..531C
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The Circumstellar Environments of NML Cygni and the Cool Hypergiants, Schuster, Michael T.; Humphreys, Roberta M.; Marengo, Massimo, The Astronomical Journal131, #1 (January 2006), pp. 603-611, Bibcode: 2006AJ....131..603S
, doi10.1086/498395.