Trumpler 27
{{Sky|17|36|20|-|33|31|00}}
{{Infobox open cluster
| name = Trumpler 27
| image = Trumpler 27.jpg
| caption =
| credit =
| epoch = J2000
| constellation = Scorpius
| dist_ly =
| dist_pc =
| appmag_v = 6.7{{cite simbad|title=Cl Trumpler 27|access-date=2020-03-31}}
| size_v = 6{{prime}} × 6{{prime}}
| age =
| notes = True nature is unknown
}}
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){{cite journal|bibcode=2013A&A...560A..76M|title=Stellar clusters in the inner Galaxy and their correlation with cold dust emission|last1=Morales|first1=Esteban F. E.|last2=Wyrowski|first2=Friedrich|last3=Schuller|first3=Frederic|last4=Menten|first4=Karl M.|journal=Astronomy and Astrophysics|year=2013|volume=560|pages=A76|doi=10.1051/0004-6361/201321626|arxiv=1310.2612|s2cid=118422539 }} to 6,800 light-years (2,100 kiloparsecs) The name refers to Robert Julius Trumpler's catalog of open clusters, published in 1930.{{cite journal|bibcode=1970A&A.....5..298T|title=A study of the southern open clusters : TR 27, TR 28, NGC 6416, NGC 6425|last1=The|first1=P. S.|last2=Stokes|first2=N.|journal=Astronomy and Astrophysics|year=1970|volume=5|pages=298}}
It was originally thought to be young open cluster in the outer edge of the Sagittarius Arm, still surrounded by interstellar matter. The light from the stars is heavily extinguished and reddened by intervening interstellar dust.{{cite journal|bibcode=1977ApJ...215..106M|title=Trumpler 27: A heavily reddened young open cluster with blue and red supergiants|last1=Moffat|first1=A. F. J.|last2=Fitzgerald|first2=M. P.|last3=Jackson|first3=P. D.|journal=The Astrophysical Journal|year=1977|volume=215|pages=106|doi=10.1086/155338}} The light coming from the stars is also significantly polarized.{{cite journal|bibcode=2000AJ....120.1906F|title=The Highly Polarized Open Cluster Trumpler 27|last1=Feinstein|first1=Carlos|last2=Baume|first2=Gustavo|last3=Vazquez|first3=Ruben|last4=Niemela|first4=Virpi|last5=Cerruti|first5=Miguel Angel|journal=The Astronomical Journal|year=2000|volume=120|issue=4|pages=1906|doi=10.1086/301562|arxiv=astro-ph/0007093|s2cid=18701893 }} 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.{{cite journal|bibcode=2012A&A...548A.125P|title=Photometric distances to young stars in the inner Galactic disk. II. The region towards the open cluster Trumpler 27 at L = 355°|last1=Perren|first1=G.|last2=Vázquez|first2=R. A.|last3=Carraro|first3=G.|journal=Astronomy and Astrophysics|year=2012|volume=548|pages=A125|doi=10.1051/0004-6361/201219653|arxiv=1209.3273| s2cid=62888409 }}
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.{{cite journal|author1=Massey, P.|author2=Degioia-Eastwood, K.|author2-link=Kathy Eastwood|author3=Waterhouse, E.|date=2001|title=The Progenitor Masses of Wolf-Rayet Stars and Luminous Blue Variables Determined from Cluster Turnoffs. II. Results from 12 Galactic Clusters and OB Associations|journal=The Astronomical Journal|volume=121|issue=2|pages=1050–1070|arxiv=astro-ph/0010654|bibcode=2001AJ....121.1050M|doi=10.1086/318769|s2cid=53345173 }} 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. Star #102 is known as V925 Scorpii or HD 159378,{{cite simbad|title=HD 159378|access-date=2020-03-31}} and is a rare yellow supergiant star.{{cite journal|bibcode=1983A&AS...52...27B|title=An investigation of the heavily reddened young open cluster TR 27 on the Walraven photometric system|last1=Bakker|first1=R.|last2=The|first2=P. S.|journal=Astronomy and Astrophysics Supplement Series|year=1983|volume=52|pages=27}}