16 Cygni or 16 Cyg is the

Flamsteed designation A Flamsteed designation is a combination of a number and constellation name that uniquely identifies most naked eye stars in the modern constellations visible from southern England. They are named for John Flamsteed who first used them while co ...

of a

triple star A star system or stellar system is a small number of stars that orbit each other, bound by gravitational attraction. A large group of stars bound by gravitation is generally called a '' star cluster'' or ''galaxy'', although, broadly speaking ...

system approximately 69

light-year A light-year, alternatively spelled light year, is a large unit of length used to express astronomical distance, astronomical distances and is equivalent to about 9.46 Orders of magnitude (numbers)#1012, trillion kilometers (), or 5.88 ...

s away from Earth in the

constellation A constellation is an area on the celestial sphere in which a group of visible stars forms a perceived pattern or outline, typically representing an animal, mythological subject, or inanimate object. The origins of the earliest constellation ...

of Cygnus. It consists of two

Sun The Sun is the star at the center of the Solar System. It is a nearly perfect ball of hot plasma, heated to incandescence by nuclear fusion reactions in its core. The Sun radiates this energy mainly as light, ultraviolet, and infrared radi ...

-like yellow dwarf stars, 16 Cygni A and 16 Cygni B, together with a

red dwarf ''Red Dwarf'' is a British science fiction comedy franchise created by Rob Grant and Doug Naylor, which primarily consists of a television sitcom that aired on BBC Two between 1988 and 1999, and on Dave since 2009, gaining a cult following. ...

, 16 Cygni C. In 1996 an

extrasolar planet An exoplanet or extrasolar planet is a planet outside the Solar System. The first possible evidence of an exoplanet was noted in 1917 but was not recognized as such. The first confirmation of detection occurred in 1992. A different planet, init ...

was discovered in an

eccentric Eccentricity or eccentric may refer to: * Eccentricity (behavior), odd behavior on the part of a person, as opposed to being "normal" Mathematics, science and technology Mathematics * Off-center, in geometry * Eccentricity (graph theory) of a v ...

orbit In celestial mechanics, an orbit is the curved trajectory of an object such as the trajectory of a planet around a star, or of a natural satellite around a planet, or of an artificial satellite around an object or position in space such as ...

around 16 Cygni B.

Distance

The parallax of the two brightest stars were measured as part of the

Hipparcos ''Hipparcos'' was a scientific satellite of the European Space Agency (ESA), launched in 1989 and operated until 1993. It was the first space experiment devoted to precision astrometry, the accurate measurement of the positions of celestial ob ...

astrometry Astrometry is a branch of astronomy that involves precise measurements of the positions and movements of stars and other celestial bodies. It provides the kinematics and physical origin of the Solar System and this galaxy, the Milky Way. Hist ...

mission. This yielded a parallax of 47.44

milliarcsecond A minute of arc, arcminute (arcmin), arc minute, or minute arc, denoted by the symbol , is a unit of angular measurement equal to of one degree. Since one degree is of a turn (or complete rotation), one minute of arc is of a turn. The n ...

s for 16 Cygni A and 47.14 milliarcseconds for 16 Cygni B. Since the two components are associated, it is reasonable to assume they lie at the same distance, so the different parallaxes are a result of experimental error (indeed, when the associated parallax errors are taken into account, the ranges of the parallaxes overlap). Using the parallax of the A component, the distance is 21.1

parsec The parsec (symbol: pc) is a unit of length used to measure the large distances to astronomical objects outside the Solar System, approximately equal to or (au), i.e. . The parsec unit is obtained by the use of parallax and trigonometry, an ...

s. The parallax of the B component corresponds to a distance of 21.2

Stellar components

16 Cygni is a hierarchical triple system. Stars A and C form a close binary with a

projected separation This glossary of astronomy is a list of definitions of terms and concepts relevant to astronomy and cosmology, their sub-disciplines, and related fields. Astronomy is concerned with the study of celestial objects and phenomena that originate outsi ...

of 73 AU. The

orbital elements Orbital elements are the parameters required to uniquely identify a specific orbit. In celestial mechanics these elements are considered in two-body systems using a Kepler orbit. There are many different ways to mathematically describe the same ...

of the A–C binary are currently unknown. At a distance of 860 AU from A is a third component designated 16 Cygni B. The

of B relative to the A–C pair was determined in 1999 and not updated since (as of June 2007): plausible orbits range in period from 18,200 to 1.3 million years, with a

semimajor axis In geometry, the major axis of an ellipse is its longest diameter: a line segment that runs through the center and both foci, with ends at the two most widely separated points of the perimeter. The semi-major axis (major semiaxis) is the lo ...

ranging from 877 to 15,180 AU. In addition B orbits between 100 and 160 degrees inclination, that is against the A–C pole such that 90 degrees would be ecliptical. Both 16 Cygni A and 16 Cygni B are yellow dwarf stars similar to the

. Their

spectral type In astronomy, stellar classification is the classification of stars based on their spectral characteristics. Electromagnetic radiation from the star is analyzed by splitting it with a prism or diffraction grating into a spectrum exhibiting the ...

s have been given as G1.5V and G3V, with A being a little hotter than the Sun, and B somewhat cooler. The system was within the field of view of the original mission of the ''

Kepler Johannes Kepler (; ; 27 December 1571 – 15 November 1630) was a German astronomer, mathematician, astrologer, natural philosopher and writer on music. He is a key figure in the 17th-century Scientific Revolution, best known for his laws o ...

'' spacecraft, which collected extremely precise photometric data of the stars. From these measurements,

asteroseismology Asteroseismology or astroseismology is the study of oscillations in stars. Stars have many resonant modes and frequencies, and the path of sound waves passing through a star depends on the speed of sound, which in turn depends on local temperatur ...

models have calculated precise masses of 1.08 and 1.04 times the

solar mass The solar mass () is a standard unit of mass in astronomy, equal to approximately . It is often used to indicate the masses of other stars, as well as stellar clusters, nebulae, galaxies and black holes. It is approximately equal to the mass ...

for 16 Cygni A and 16 Cygni B respectively, and independent ages of around 7 billion years for each star. The system has also been observed through

interferometry Interferometry is a technique which uses the '' interference'' of superimposed waves to extract information. Interferometry typically uses electromagnetic waves and is an important investigative technique in the fields of astronomy, fiber o ...

, which allowed the determination of the

angular diameter The angular diameter, angular size, apparent diameter, or apparent size is an angular distance describing how large a sphere or circle appears from a given point of view. In the vision sciences, it is called the visual angle, and in optics, it ...

of each star. The angular diameters together with the asteroseismology models were used to calculate radii of 1.229 and 1.116 times the

solar radius Solar radius is a unit of distance used to express the size of stars in astronomy relative to the Sun. The solar radius is usually defined as the radius to the layer in the Sun's photosphere where the optical depth equals 2/3: :1\,R_ = 6.9 ...

for components A and B respectively.

Abundances

Despite having the same age and presumably the same primordial composition, observations show a small difference in the

metallicity In astronomy, metallicity is the abundance of elements present in an object that are heavier than hydrogen and helium. Most of the normal physical matter in the Universe is either hydrogen or helium, and astronomers use the word ''"metals"'' as ...

of the two 16 Cygni stars. The primary star has an iron abundance of 1.26 times the solar value, compared to 1.13 for the secondary star. A similar trend has been found for all other metals, with the primary component having an average of 10% more metals than B. One possibility is that this difference is linked to the planet 16 Cygni Bb, since its formation may have removed metals from the

protoplanetary disk A protoplanetary disk is a rotating circumstellar disc of dense gas and dust surrounding a young newly formed star, a T Tauri star, or Herbig Ae/Be star. The protoplanetary disk may also be considered an accretion disk for the star itself, be ...

around 16 Cygni B. However, another study found no difference in heavy element abundances between 16 Cygni A and B. Another chemical peculiarity between the stars is in their

lithium Lithium (from el, λίθος, lithos, lit=stone) is a chemical element with the symbol Li and atomic number 3. It is a soft, silvery-white alkali metal. Under standard conditions, it is the least dense metal and the least dense soli ...

abundance. Measurements of the lithium abundance in the system show a 4 times higher abundance in component A than in 16 Cygni B. Compared to the Sun, 16 Cygni A has 1.66 as much lithium, while 16 Cygni B has only 0.35. It has been hypothesized that the

accretion Accretion may refer to: Science * Accretion (astrophysics), the formation of planets and other bodies by collection of material through gravity * Accretion (meteorology), the process by which water vapor in clouds forms water droplets around nucl ...

of about 1

Earth mass An Earth mass (denoted as M_\mathrm or M_\oplus, where ⊕ is the standard astronomical symbol for Earth), is a unit of mass equal to the mass of the planet Earth. The current best estimate for the mass of Earth is , with a relative uncertainty ...

of metals by 16 Cygni B soon after the system's formation may have destroyed the lithium in the star's atmosphere. Another proposed scenario is the engulfment of a Jupiter-mass planet by 16 Cygni A, which increased the amount of lithium in the star's outer atmosphere.

Planetary system

In 1996 an

in an

orbit was announced around the star 16 Cygni B. The discovery by the

radial velocity method Doppler spectroscopy (also known as the radial-velocity method, or colloquially, the wobble method) is an indirect method for finding extrasolar planets and brown dwarfs from radial-velocity measurements via observation of Doppler shifts in th ...

was made from independent observations from the

McDonald Observatory McDonald Observatory is an astronomical observatory located near unincorporated community of Fort Davis in Jeff Davis County, Texas, United States. The facility is located on Mount Locke in the Davis Mountains of West Texas, with additional fac ...

and

Lick Observatory The Lick Observatory is an astronomical observatory owned and operated by the University of California. It is on the summit of Mount Hamilton, in the Diablo Range just east of San Jose, California, United States. The observatory is managed by t ...

. The planet's orbit takes 799.5 days to complete, with a semimajor axis of 1.69 AU. It has a very high eccentricity of 0.69, which might be the result of gravitational perturbations from 16 Cygni A. In particular, simulations show the planet's eccentricity oscillates between low and high values in timescales of tens of millions of years. Like the majority of extrasolar planets detectable from Earth,

16 Cygni Bb 16 Cygni Bb or HD 186427 b is an extrasolar planet approximately away in the constellation of Cygnus. The planet was discovered orbiting the Sun-like star 16 Cygni B, one of two solar-mass () components of the triple star system 16 Cygni in 1 ...

was deduced from the

radial velocity The radial velocity or line-of-sight velocity, also known as radial speed or range rate, of a target with respect to an observer is the rate of change of the distance or range between the two points. It is equivalent to the vector projection ...

of its parent star. At the time that only gave a lower limit on the mass: in this case, about 1.68 times that of

Jupiter Jupiter is the fifth planet from the Sun and the largest in the Solar System. It is a gas giant with a mass more than two and a half times that of all the other planets in the Solar System combined, but slightly less than one-thousand ...

. In 2012, two astronomers, E. Plavalova and N.A. Solovaya, showed that the stable orbit would demand about 2.38

Jupiter mass Jupiter mass, also called Jovian mass, is the unit of mass equal to the total mass of the planet Jupiter. This value may refer to the mass of the planet alone, or the mass of the entire Jovian system to include the moons of Jupiter. Jupiter is by ...

es, such that its orbit was inclined at either 45° or 135°. The eccentric orbit and mass of 16 Cygni Bb makes it extremely unlikely that a terrestrial sized planet will be found orbiting within the star's habitable zone. For the 16 Cyg B system, only particles inside approximately 0.3 AU remained stable within a million years of formation, leaving open the possibility of short-period planets. For them, observation rules out any such planet of over a Neptune mass. There was a METI message sent to the 16 Cygni system. It was transmitted from

Eurasia Eurasia (, ) is the largest continental area on Earth, comprising all of Europe and Asia. Primarily in the Northern and Eastern Hemispheres, it spans from the British Isles and the Iberian Peninsula in the west to the Japanese archipelag ...

's largest

radar Radar is a detection system that uses radio waves to determine the distance (''ranging''), angle, and radial velocity of objects relative to the site. It can be used to detect aircraft, Marine radar, ships, spacecraft, guided missiles, motor v ...

—the 70-meter (230-foot) Eupatoria Planetary Radar. The message was named

Cosmic Call 1 Cosmic commonly refers to: * The cosmos, a concept of the universe Cosmic may also refer to: Media * ''Cosmic'' (album), an album by Bazzi * Afro/Cosmic music * "Cosmic", a song by Kylie Minogue from the album '' X'' * CosM.i.C, a member of ...

; it was sent on May 24, 1999, and it will reach 16 Cygni in November 2069. http://www.cplire.ru/rus/ra&sr/VAK-2004.html

References

External links