SAO 20575 or BD+60°2522 is a bright O-class star that has produced the Bubble Nebula (NGC 7635) with its stellar wind. The exact classification of the star is uncertain, with a number of spectral peculiarities and inconsistencies between the appearance of the star itself and the effects on the nearby nebulosity, but it is undoubtedly a highly luminous hot massive star. Direct spectroscopy yields a spectral class of O6.5 and an effective temperature around 37,500K.
^ abcMoore, B. D.; Walter, D. K.; Hester, J. J.; Scowen, P. A.; Dufour, R. J.; Buckalew, B. A. (2002). "\ITAL]Hubble Space Telescope\/ITAL] Observations of the Windblown Nebula NGC 7635". The Astronomical Journal124 (6): 3313. doi:10.1086/344596.edit