Trumpler 27

Trumpler 27 is a possible open cluster in the southern constellation Scorpius. If it exists, it is a few thousand light-years away from the Sun, with estimates ranging from 3,900 light-years (1,210 kiloparsecs)[3] to 6,800 light-years (2,100 kiloparsecs)[4] The name refers to Robert Julius Trumpler's catalog of open clusters, published in 1930.[5]

Trumpler 27
Observation data (J2000 epoch)
Right ascension	17h 36m 20s[1]
Declination	−33° 31.0′[1]
Apparent magnitude (V)	6.7[1]
Apparent dimensions (V)	6′ × 6′[1]
Physical characteristics
True nature is unknown[2]
Other designations	C 1732-334[1]
Associations
Constellation	Scorpius

It was originally thought to be young open cluster in the outer edge of the Sagittarius Arm, still surrounded by interstellar matter.[5] The light from the stars is heavily extinguished and reddened by intervening interstellar dust.[4] The light coming from the stars is also significantly polarized.[6] However, a close study in 2012 could not confirm whether the stars truly form a cluster, or if they are a close alignment of bright stars.[2]

Several member stars have been studied in closer detail. Star #1 of Trumpler 27 is CD−33°12241, a red supergiant star with a spectral type of M0Ia. Stars #28 and #105 are Wolf-Rayet stars.[4][7] Star #27, a blue giant star with a spectral type of O8III((f)), may be one of the most luminous stars known, with a bolometric magnitude of −10.5.[7] Star #102 is known as V925 Scorpii or HD 159378,[8] and is a rare yellow supergiant star.[9]