V1191 Cygni is thevariable star designation for anovercontact binarystar system in the constellationCygnus.[13] First found to be variable in 1965, it is aW Ursae Majoris variable with a maximumapparent magnitude 10.82. It drops by 0.33 magnitudes during primary eclipses with a period of 0.3134 days, while dropping by 0.29 magnitudes during secondary eclipses.[11] The primary star, which is also the cooler star, appears to have aspectral type of F6V, while the secondary is slightly cooler with a spectral type of G5V.[4] With a mass of 1.29solar masses and a luminosity of 2.71solar luminosities, it is slightly more massive and luminous than the sun, while the secondary is only around 1/10 as massive and less than half as luminous. With a separation of 2.20solar radii, themass transfer of about 2×10−7 solar masses per year from the secondary to the primary is one of the highest known for a system of its type.[10]
V1191 Cygni is a W-type W UMa variable,[8] meaning that the primary eclipse occurs when the less-massive component is eclipsed by the larger, more massive component, although the masses are unusually different for such a system.[14] The current period is very short for a system of its spectral type, suggesting that the stars are relatively small for their mass and age,[14] which is likely around 3.85 billion years.[12] The pair's orbital period is increasing at a rate of over 4×10−7 days per year, one of the fastest known rates amongcontact binary systems,[8] likely due to the high rate of mass transfer. In addition to the period increase, there is cyclic period change of 0.023 days over 26.7 years, caused by either a third body with a mass of 0.77 solar masses ormagnetic activity cycles. The mass transfer will likely eventually cause the system to evolve into a single star with a very high rotation rate.[13]
^Ivanov, G. A. (2008). "Catalogue of stars with high-proper motions - version 2".Kinematika I Fizika Nebesnykh Tel.24: 480.Bibcode:2008KFNT...24..480I.
^abcCutri, Roc M.; Skrutskie, Michael F.; Van Dyk, Schuyler D.; Beichman, Charles A.; Carpenter, John M.; Chester, Thomas; Cambresy, Laurent; Evans, Tracey E.; Fowler, John W.; Gizis, John E.; Howard, Elizabeth V.; Huchra, John P.; Jarrett, Thomas H.; Kopan, Eugene L.; Kirkpatrick, J. Davy; Light, Robert M.; Marsh, Kenneth A.; McCallon, Howard L.; Schneider, Stephen E.; Stiening, Rae; Sykes, Matthew J.; Weinberg, Martin D.; Wheaton, William A.; Wheelock, Sherry L.; Zacarias, N. (2003)."VizieR Online Data Catalog: 2MASS All-Sky Catalog of Point Sources (Cutri+ 2003)".CDS/ADC Collection of Electronic Catalogues.2246: II/246.Bibcode:2003yCat.2246....0C.
^Mayer, P (1965). "Two new variable stars in the Cygnus".Bulletin of the Astronomical Institute of Czechoslovakia.16:255–256.Bibcode:1965BAICz..16..255M.
^abRucinski, S. M.; Pribulla, T.; Mochnacki, S. W.; Liokumovich, E.; Lu, W.; Debond, H.; De Ridder, A.; Karmo, T.; Rock, M.; Thomson, J. R.; Ogłoza, W.; Kaminski, K.; Ligeza, P. (2008). "Radial Velocity Studies of Close Binary Stars. Xiii".The Astronomical Journal.136 (2):586–593.arXiv:0805.1695.Bibcode:2008AJ....136..586R.doi:10.1088/0004-6256/136/2/586.S2CID119225926.
