3 Geminorum Explained

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.^[1] There is also a much fainter, approximately 14th magnitude, star 14" away.^[2]

Faint Hα emission lines have been detected in the spectrum of 3 Geminorum,^[3] 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.^[4] 3 Geminorum has frequently been classified as a normal supergiant (luminosity class Ib),^[5] 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.^[6]

Notes and References

1. 2005AJ....130.2262R. Adaptive Optics Photometry and Astrometry of Binary Stars. The Astronomical Journal. 130. 5. 2262. 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. 10.1086/491586. free.
2. 2001AJ....122.3466M. The 2001 US Naval Observatory Double Star CD-ROM. I. The Washington Double Star Catalog. The Astronomical Journal. 122. 6. 3466. Mason. Brian D.. Wycoff. Gary L.. Hartkopf. William I.. Douglass. Geoffrey G.. Worley. Charles E.. 2001. 10.1086/323920. free.
3. 1973ApJ...186..909R. A survey of H-alpha emission in early-type high-luminosity stars. Astrophysical Journal. 186. 909. Rosendhal. J. D.. 1973. 10.1086/152555.
4. 1999A&AS..134..255K. Catalogue of H-alpha emission stars in the Northern Milky Way. Astronomy and Astrophysics Supplement. 134. 2. 255. Kohoutek. L.. Wehmeyer. R.. 1999. 10.1051/aas:1999101. free.
5. 2014yCat....1.2023S. 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. Skiff. B. A.. 2014.
6. 1995A&AS..110..107M. Observations of lunar occultations at Observatoire de la Cote d'Azur. Astronomy and Astrophysics Supplement. 110. 107. Meyer. C.. Rabbia. Y.. Froeschle. M.. Helmer. G.. Amieux. G.. 1995.