V1191 Cygni is the
variable star designation for an
overcontact binarystar system in the constellation
Cygnus.[13] First found to be variable in 1965, it is a
W Ursae Majoris variable with a maximum
apparent 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 a
spectral type of F6V, while the secondary is slightly cooler with a spectral type of G5V.[4] With a mass of 1.29
solar masses and a luminosity of 2.71
solar 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 2.20
solar radii, the
mass 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 among
contact 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 or
magnetic 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.
^Droege, Thomas F.; Richmond, Michael W.; Sallman, Michael P.; Creager, Robert P. (2006). "TASS Mark IV Photometric Survey of the Northern Sky". Publications of the Astronomical Society of the Pacific. 118 (850): 1666–1678.
arXiv:astro-ph/0610529.
Bibcode:
2006PASP..118.1666D.
doi:
10.1086/510197.
S2CID11716917.
^
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.
^
abcPribulla, T.; Vaňko, M.; Chochol, D. R.; Parimucha, Š.; Baluďanský, D. (2005). "Ccd Photometry of the Neglected Contact Binaries V344 Lac and V1191 Cyg". Astrophysics and Space Science. 296 (1–4): 281–284.
Bibcode:
2005Ap&SS.296..281P.
doi:
10.1007/s10509-005-4831-2.
S2CID189843557.
^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.