61 Cygni Totally Explained

Everything about 61 Cygni totally explained

| metal=[Fe/H] = -0.20/-0.27 | gravity=4.40/4.20 | radius=0.72/0.67 | rotation=37/— days | luminosity=0.085/0.039 | temperature=4,640/4,440 However, by 1917 refined measured parallax differences had reduced the separation significantly, and the binary nature of this system was clear by 1934 with orbital elements being published.

Properties

Although it appears to be a single star to the naked eye, 61 Cygni is in fact a widely separated binary system, composed of two K class (orange) main sequence stars, 61 Cygni A and 61 Cygni B. The brighter star 61 Cygni A is of apparent magnitude 5.2, the fainter 61 Cygni B is 6.1. Both appear to be old disk stars, with an estimated age that's older than the Sun. The system has a net space velocity of 108 km/s relative to the Sun, which results in the high proper motion across the sky.
   Component A is the slightly more massive of the pair. It has an activity cycle that's much more pronounced than the solar sunspot cycle. This is a complex activity cycle that varies with a period of about 7.5±1.7 years. (An earlier estimate gave a period of 7.3 years.) The combination of starspot activity combined with rotation and chromospheric activity is characteristic of a BY Draconis variable.
   Component B displays a more chaotic pattern of variability than A, with significant short-term flares. There is an 11.7 year periodicity to the overall activity cycle of B.
   An observer using 7×50 binoculars can find 61 Cygni two binocular fields south-east of the bright star Deneb. The angular separation of the two stars is slightly greater than the angular size of Saturn (16–20″). So, under ideal seeing conditions, the binary system can be resolved by a telescope with a 6 mm aperture. This is well within the capability of a typical pair of binoculars.

Possible low-mass companions

On several occasions it has been claimed that 61 Cygni has unseen low-mass companions, planets or a brown dwarf. Kaj Strand made the first such claim in 1942 using observations to detect tiny but systematic variations in the orbital motions of 61 Cygni A and B. These perturbations suggested that a third body was orbiting 61 Cygni A. In 1957 additional data allowed him to narrow his uncertainties, claiming that the object appeared to have about eight times the mass of Jupiter. With a calculated orbital period of 4.8 years, the estimated semi-major axis of 2.4 A.U. In 1977 Soviet astronomers at the Pulkovo Observatory near St Petersburg suggested that the system included three planets: two giant planets with six and twelve Jupiter masses around 61 Cyg A, and one giant planet with seven Jupiter masses around 61 cygni B. In 1978 Wulff Dieter Heintz suggested these claims were "spurious", having failed to detect any evidence of such motion down to six percent of the Sun's mass—equivalent to about 60 times the mass of Jupiter.
Because of the proximity of this system to the Sun, it's a frequent target of interest for astronomers. Both stars were selected by NASA as "Tier 1" targets for the proposed optical Space Interferometry Mission. This mission is potentially capable of detecting planets with as little as 3 times the mass of the Earth at an orbital distance of 2 A.U. from the star. Measurements of this system have detected an excess of far infrared radiation, beyond what is emitted by the stars. Such an excess is sometimes associated with a disk of dust, but in this case it lies sufficiently close to one or both of the stars that it hasn't yet been resolved with a telescope.

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