Delta Circini (δ Cir), is a multiple star system located in the constellation Circinus. Delta Circini is also known as HR 5664, and HD 135240. The system has a combined apparent visual magnitude of +5.09, and is located at a distance of 770 pc (2,500ly) from the Sun.
δ Circini B is a 13th magnitude companion nearly an arc-second away. It is unclear whether the two are physically associated and little is known about the fainter star although it has been reported to be a G5 main sequence star or giant.
HD 135160 is a 6th magnitude binary Be star that shares a common space motion with δ Circini and is only 4 arc minutes away. The two make a faint naked eye pair.
All three components of δ Circini A are hot luminous stars. The brightest is an O8 star just beginning to evolve away from the main sequence. It is in a very close orbit with an O9.5 main sequence star. The two stars are deformed into ellipsoidal shapes and eclipse each other every 3.9 days. The total brightness change is only 0.15 magnitudes.
The third component is a B0.5 main sequence star in a long eccentric orbit around the close pair. It is fainter and cooler than either of the two close stars, yet it is calculated to be more massive than δ Cir A, so it is suspected that it may also be a close binary system.
- Mayer, Pavel; Harmanec, Petr; Sana, Hugues; Le Bouquin, Jean-Baptiste (2014). "The Three-body System δ Circini". The Astronomical Journal 148 (6): 114. doi:10.1088/0004-6256/148/6/114. Bibcode: 2014AJ....148..114M.
- Lindroos, K. P. (1985). "A study of visual double stars with early type primaries. IV Astrophysical data". Astronomy and Astrophysics Supplement Series 60: 183. Bibcode: 1985A&AS...60..183L.
- "del Cir". SIMBAD. Centre de données astronomiques de Strasbourg. http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=del+Cir.
- Delta Circini on WikiSky: DSS2, SDSS, GALEX, IRAS, Hydrogen α, X-Ray, Astrophoto, Sky Map, Articles and images
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