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3 Geminorum

Location of 3 Gem (circled)
Observation data Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation	Gemini
Right ascension	06 09 43.9853
Declination	+23° 06′ 48.472″
Apparent magnitude (V)	5.71 - 5.77
Characteristics
Evolutionary stage	Blue supergiant star
Spectral type	B3Ia
U−B color index	−0.63
B−V color index	+0.21
Variable type	α Cyg
Astrometry
Radial velocity (Rv)	16.00±4.3 km/s
Proper motion (μ)	RA: −0.064 mas/yr Dec.: −2.685 mas/yr
Parallax (π)	0.3878 ± 0.0616 mas
Distance	approx. 8,000 ly (approx. 2,600 pc)
Absolute magnitude (MV)	−6.26
Details
Mass	21 M☉
Radius	55 R☉
Luminosity	204,000 L☉
Surface gravity (log g)	2.45 cgs
Temperature	16,500 K
Rotational velocity (v sin i)	80 km/s
Other designations
3 Geminorum, PU Gem, HR 2173, HIP 29225, HD 42087, BD+23°1226, AAVSO 0603+23
Database references
SIMBAD	data

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 with a main period of 6.807 days and a secondary period of 25 days.

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. There is also a much fainter, approximately 14th magnitude, star 14" away.

Faint Hα emission lines have been detected in the spectrum of 3 Geminorum, but this is not usually expressed in published spectral classifications. An "e" is only occasionally appended to the spectral type to reflect the emission lines. 3 Geminorum has frequently been classified as a normal supergiant (luminosity class Ib), although a bright supergiant (Ia) luminosity class is now preferred.

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.

References

1. ^ Brown, A. G. A.; et al. (Gaia collaboration) (2021). "Gaia Early Data Release 3: Summary of the contents and survey properties". Astronomy & Astrophysics. 649: A1. arXiv:2012.01533. Bibcode:2021A&A...649A...1G. doi:10.1051/0004-6361/202039657. S2CID 227254300. (Erratum: doi:10.1051/0004-6361/202039657e). Gaia EDR3 record for this source at VizieR.
2. ^ "PU Gem". Variable Star Index. Retrieved 2022-05-22.
3. ^ 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. ISBN 978-94-010-2629-1.
4. ^ 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.
5. ^ Samus, N. N.; Durlevich, O. V.; et al. (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.
6. Gontcharov, G. A. (2006). "Pulkovo Compilation of Radial Velocities for 35 495 Hipparcos stars in a common system". Astronomy Letters. 32 (11): 759–771. arXiv:1606.08053. Bibcode:2006AstL...32..759G. doi:10.1134/S1063773706110065. S2CID 119231169.
7. ^ 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. S2CID 1552752.
8. ^ Haucke, M.; et al. (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. S2CID 126150688. A91.
9. "Hipparcos Tools Interactive Data Access". Hipparcos. ESA. Retrieved 8 December 2021.
10. Roberts, Lewis C.; Turner, Nils H.; Bradford, L. William; Ten Brummelaar, Theo A.; Oppenheimer, Ben R.; Kuhn, Jeff R.; Whitman, Kathryn; Perrin, Marshall D.; Graham, James R. (2005). "Adaptive Optics Photometry and Astrometry of Binary Stars". The Astronomical Journal. 130 (5): 2262. Bibcode:2005AJ....130.2262R. doi:10.1086/491586.
11. Mason, Brian D.; Wycoff, Gary L.; Hartkopf, William I.; Douglass, Geoffrey G.; Worley, Charles E. (2001). "The 2001 US Naval Observatory Double Star CD-ROM. I. The Washington Double Star Catalog". The Astronomical Journal. 122 (6): 3466. Bibcode:2001AJ....122.3466M. doi:10.1086/323920.
12. 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.
13. Kohoutek, L.; Wehmeyer, R. (1999). "Catalogue of H-alpha emission stars in the Northern Milky Way". Astronomy and Astrophysics Supplement. 134 (2): 255. Bibcode:1999A&AS..134..255K. doi:10.1051/aas:1999101.
14. 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.
15. 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.

v t e Constellation of Gemini
List of stars in Gemini Gemini in Chinese astronomy
Stars	Bayer α (Castor) β (Pollux) γ (Alhena) δ (Wasat) ε (Mebsuta) ζ (Mekbuda) η (Propus) θ ι κ λ μ (Tejat) ν ξ (Alzirr) ο (Jishui) π ρ σ τ υ φ χ ω Flamsteed 1 3 6 25 30 37 38 (e) 57 (A) 64 (b) 65 (b) 74 (f) 81 (g) Variable R U TV BG DM DN OU WY V429 HR 2877 HD 44780 50554 63433 260655 Other 2MASS 0727+1710 CXOU J061705.3+222127 Geminga Gliese 251 HAT-P-20 HAT-P-24 HAT-P-33 LB-1 PSR J0659+1414 WD J0651+2844 WISEP J060738.65+242953.4
Exoplanets HAT-P-24b HAT-P-50b HD 50554 b HD 59686 Ab Pollux b τ Geminorum b
Star clusters	NGC 2129 2158 2266 2277 2355 2420 Other Koposov 2 Messier 35
Nebulae IC 443 IC 444 Medusa Nebula NGC 2371-2 NGC 2392
Galaxies	NGC 2291 2294 2357 Other 2MASX J07322028+3138009 IC 485 PKS 0735+178
Astronomical events GRB 070125
Category

• Gemini (constellation)
• Henry Draper Catalogue objects
• Alpha Cygni variables
• Flamsteed objects
• Bright Star Catalogue objects
• Objects with variable star designations
• Durchmusterung objects
• Hipparcos objects
• B-type supergiants