Kappa Herculis (κ Herculis, abbreviated Kappa Her, κ Her) is an optical double star in the constellation of Hercules. The two components, Kappa Herculis A (Marsic/ˈmɑːrsɪk/, the traditional name of the system)[15] and B, were 27.3 arc seconds apart in 2000. Based on parallax measurements from the Hipparcos mission, κ Her A is about 113 parsecs (370 light-years) from the Sun and κ Her B is 600 parsecs (2,000 light-years); more recent parallax measurements suggest that B is around 5% more distant than A.
A faint third component Kappa Herculis C is just over 1 arc-minute away.[16] It is at the same distance as κ Her A and has an almost-identical space motion.[17]
The system bore the traditional names of "Marsic", "Marfik" or "Marfak", all of which come from the Arabic لمرفق Al-Mirfaq meaning "the elbow",[19] a name (or some derivative of which) it shared with Lambda Ophiuchi. The Working Group on Star Names (WGSN) approved the name Marsic for the component Kappa Herculis A on February 1, 2017, and Marfik for the primary component of Lambda Ophiuchi on September 12, 2016, and they are both now so included in the List of IAU-approved Star Names.[20]
Kappa Herculis A is a giant star with stellar classification G8III. With a mass of three M☉ and radius that is 16 R☉, the star boasts a bolometric luminosity that is 148 L☉. Its slightly companion is cooler and about a third of the luminosity.
Kappa Herculis is a suspected variable star with a reported magnitude range of 4.70 to 5.02.[6]
^Høg, E.; Fabricius, C.; Makarov, V. V.; Urban, S.; Corbin, T.; Wycoff, G.; Bastian, U.; Schwekendiek, P.; Wicenec, A. (2000). "The Tycho-2 catalogue of the 2.5 million brightest stars". Astronomy and Astrophysics. 355: L27. Bibcode:2000A&A...355L..27H.
^ abSamus, 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.
^ abDe Medeiros, J. R.; Do Nascimento, J. D.; Sankarankutty, S.; Costa, J. M.; Maia, M. R. G. (2000). "Rotation and lithium in single giant stars". Astronomy and Astrophysics. 363: 239. arXiv:astro-ph/0010273. Bibcode:2000A&A...363..239D.
^Hessman, F. V.; Dhillon, V. S.; Winget, D. E.; Schreiber, M. R.; Horne, K.; Marsh, T. R.; Guenther, E.; Schwope, A.; Heber, U. (2010). "On the naming convention used for multiple star systems and extrasolar planets". arXiv:1012.0707 [astro-ph.SR].