O-type star
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An O-type star is a hot, blue-white star of spectral type O in the Yerkes classification system employed by astronomers. They have temperatures in excess of 30,000 kelvins (K). Stars of this type have strong absorption lines of ionised helium, strong lines of other ionised elements, and hydrogen and neutral helium lines weaker than spectral type B.
The Trifid Nebula (M20) is sculpted and lit by the luminous O7.5III star visible at its centre in this infrared image.
The central star of NGC 6826 is a low-mass O6 star.
Alnitak is a triple star system with an O9.7 supergiant and an O9 giant as well as a B0 giant. These stars illuminate the nearby Flame Nebula.
The brightest star in the Trapezium cluster is O7V star θ 1 Orionis C. The other three are B0.5 and B1 main-sequence stars.
Cygnus OB2
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Cygnus OB2 is an OB association that is home to some of the most massive and most luminous stars known, including suspected Luminous blue variable Cyg OB2 #12. It also includes one of the largest known stars, NML Cygni. The region is embedded within a wider one of star formation known as Cygnus X, which is one of the most luminous objects in the sky at radio wavelengths. The region is approximately 1,570 parsecs from Earth in the constellation of Cygnus.
Open cluster Bica 1
Part of open cluster Bica 2