V1191 Cygni
V1191 Cygni is the variable star designation for an overcontact binary star system in the constellation Cygnus.[12] 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.[10] 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.[3] 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.[9]
V1191 Cygni is a W-type W UMa variable,[7] 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.[13] 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,[13] which is likely around 3.85 billion years.[11] 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,[7] 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.[12]
References
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- ↑ 11.0 11.1 11.2 11.3 Lua error in package.lua at line 80: module 'strict' not found.
- ↑ 12.0 12.1 Lua error in package.lua at line 80: module 'strict' not found.
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