3 Geminorum is a blue supergiant star in the constellation Gemini. It is a small amplitude pulsating variable and a close double star, with a mean combined apparent visual magnitude of about 5.7.
3 Geminorum was found to be an α Cygni variable in 1998 and given the designation PU Geminorum. It varies by a few tenths of a magnitude[5] with a main period of 6.807 days[2] and a secondary period of 25 days.[8]
3 Geminorum is also a close double star. The brighter component is the variable blue supergiant. The companion is 2.5 magnitudes fainter. The separation is about 0.6 arc-seconds.[10] There is also a much fainter, approximately 14th magnitude, star 14" away.[11]
Faint Hα emission lines have been detected in the spectrum of 3 Geminorum,[12] but this is not usually expressed in published spectral classifications.[3] An "e" is only occasionally appended to the spectral type to reflect the emission lines.[13][5] 3 Geminorum has frequently been classified as a normal supergiant (luminosity class Ib),[14] although although a bright supergiant (Ia) luminosity class is now preferred.[3]
3 Geminorum can be occulted by the Moon. Observations of these occultations can give information about the angular diameter of a star, or about close companions. Occultations of 3 Geminorum have been observed, but no double or diameter information has been published.[15]
"PU Gem". Variable Star Index. Retrieved 2022-05-22.
Herman, R. (1973). "Classification des éTOILES B à Partir des Raises de l'HYDROGèNE-COMPARAISON avec d'Autres Classificaitons". Spectral Classification and Multicolour Photometry. 50: 17. Bibcode:1973IAUS...50...17H. doi:10.1007/978-94-010-2627-7_3. ISBN978-94-010-2629-1.
Ducati, J. R. (2002). "VizieR Online Data Catalog: Catalogue of Stellar Photometry in Johnson's 11-color system". CDS/ADC Collection of Electronic Catalogues. 2237. Bibcode:2002yCat.2237....0D.
Samus, N. N.; Durlevich, O. V.; etal. (2009). "VizieR Online Data Catalog: General Catalogue of Variable Stars (Samus+ 2007-2013)". VizieR On-line Data Catalog: B/GCVS. Originally Published in: 2009yCat....102025S. 1. Bibcode:2009yCat....102025S.
Searle, S. C.; Prinja, R. K.; Massa, D.; Ryans, R. (2008). "Quantitative studies of the optical and UV spectra of Galactic early B supergiants. I. Fundamental parameters". Astronomy and Astrophysics. 481 (3): 777. arXiv:0801.4289. Bibcode:2008A&A...481..777S. doi:10.1051/0004-6361:20077125. S2CID1552752.
Haucke, M.; etal. (June 2018). "Wind properties of variable B supergiants. Evidence of pulsations connected with mass-loss episodes". Astronomy & Astrophysics. 614: 28. arXiv:1902.01341. Bibcode:2018A&A...614A..91H. doi:10.1051/0004-6361/201731678. A91.
Rosendhal, J. D. (1973). "A survey of H-alpha emission in early-type high-luminosity stars". Astrophysical Journal. 186: 909. Bibcode:1973ApJ...186..909R. doi:10.1086/152555.
Skiff, B. A. (2014). "VizieR Online Data Catalog: Catalogue of Stellar Spectral Classifications (Skiff, 2009-2016)". VizieR On-line Data Catalog: B/Mk. Originally Published in: Lowell Observatory (October 2014). 1. Bibcode:2014yCat....1.2023S.
Meyer, C.; Rabbia, Y.; Froeschle, M.; Helmer, G.; Amieux, G. (1995). "Observations of lunar occultations at Observatoire de la Cote d'Azur". Astronomy and Astrophysics Supplement. 110: 107. Bibcode:1995A&AS..110..107M.
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