. "O4.5" . "blue stars" . "class O star" . "O6" . "O3" . . "blue main-sequence stars" . "O4.5III(f)" . "O" . "O-type star" . "blue stellar objects" . . "class O4-5 star" . "O7" . "O(f)N6.5V" . "O6.5Iaf⁺" . "type O star" . "O-type" . "O7.5" . "O-class stars" . . "O9" . "O7.5III star" . . "O-type star" . "type O" . "O class stars" . "Massive stars" . "O7V" . "spectral class O" . "O-" . "O3-class" . "O8 star" . "blue star" . "O star" . "O5" . "spectral types O" . .