70 Ophiuchi
Encyclopedia
70 Ophiuchi a binary
Binary star
A binary star is a star system consisting of two stars orbiting around their common center of mass. The brighter star is called the primary and the other is its companion star, comes, or secondary...

 star system
Star system
A star system or stellar system is a small number of stars which orbit each other, bound by gravitational attraction. A large number of stars bound by gravitation is generally called a star cluster or galaxy, although, broadly speaking, they are also star systems.-Binary star systems:A stellar...

 located 16.6 light years away from the Earth
Earth
Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...

. It is in the constellation
Constellation
In modern astronomy, a constellation is an internationally defined area of the celestial sphere. These areas are grouped around asterisms, patterns formed by prominent stars within apparent proximity to one another on Earth's night sky....

 Ophiuchus
Ophiuchus
Ophiuchus is a large constellation located around the celestial equator. Its name is from the Greek "serpent-bearer", and it is commonly represented as a man grasping the snake that is represented by the constellation Serpens. Ophiuchus was one of the 48 constellations listed by the 2nd-century...

. At magnitude 4
Apparent magnitude
The apparent magnitude of a celestial body is a measure of its brightness as seen by an observer on Earth, adjusted to the value it would have in the absence of the atmosphere...

 it is a typical less bright star usually visible to the unaided eye away from city lights.

Binary star

The primary star is a yellow-orange main sequence
Main sequence
The main sequence is a continuous and distinctive band of stars that appears on plots of stellar color versus brightness. These color-magnitude plots are known as Hertzsprung–Russell diagrams after their co-developers, Ejnar Hertzsprung and Henry Norris Russell...

 dwarf BY Draconis
BY Draconis
BY Draconis is a multi-star system in the constellation Draco. It consists of at least three components. Components A and B form a close binary star system with a short orbital period of only 5.98 days. These may be pre-main sequence objects that are still in the process of collapsing. Their...

 variable
BY Draconis variable
BY Draconis variables are main sequence variable stars of late spectral types, usually K or M. The name comes from the archetype for this category of variable star system, BY Draconis. They exhibit variations in their luminosity due to rotation of the star coupled with star spots, and other...

 of spectral type K0, and the secondary star is an orange main sequence
Main sequence
The main sequence is a continuous and distinctive band of stars that appears on plots of stellar color versus brightness. These color-magnitude plots are known as Hertzsprung–Russell diagrams after their co-developers, Ejnar Hertzsprung and Henry Norris Russell...

 dwarf of spectral type K4. The two stars orbit each other at an average distance of 23.2 AUs
Astronomical unit
An astronomical unit is a unit of length equal to about or approximately the mean Earth–Sun distance....

. But since the orbit is highly elliptical (at e=0.499), the separation between the two varies from 11.4 to 34.8 AUs, with one orbit taking 83.38 years to complete.

History

This star system was first cataloged by William Herschel
William Herschel
Sir Frederick William Herschel, KH, FRS, German: Friedrich Wilhelm Herschel was a German-born British astronomer, technical expert, and composer. Born in Hanover, Wilhelm first followed his father into the Military Band of Hanover, but emigrated to Britain at age 19...

 in the late 18th century in his study of binary stars. Herschel proved that this system as a gravitationally bound binary
Binary star
A binary star is a star system consisting of two stars orbiting around their common center of mass. The brighter star is called the primary and the other is its companion star, comes, or secondary...

 system where the two stars orbited around a common center of mass
Center of mass
In physics, the center of mass or barycenter of a system is the average location of all of its mass. In the case of a rigid body, the position of the center of mass is fixed in relation to the body...

. This was an important contribution to the proof that Newton's law of universal gravitation
Newton's law of universal gravitation
Newton's law of universal gravitation states that every point mass in the universe attracts every other point mass with a force that is directly proportional to the product of their masses and inversely proportional to the square of the distance between them...

 applied to objects beyond the solar system
Solar System
The Solar System consists of the Sun and the astronomical objects gravitationally bound in orbit around it, all of which formed from the collapse of a giant molecular cloud approximately 4.6 billion years ago. The vast majority of the system's mass is in the Sun...

. He commented at the time that there was a possible third unseen companion affecting the orbit of the two visible stars.

Claims of a planetary system

In 1855, Capt. W. S. Jacob of the Madras Observatory
Madras Observatory
The Madras Observatory was founded by the British East India Company in 1786 in Chennai . For over a century it was the only astronomical observatory in India that exclusively worked on the stars. Among the astronomers at the observatory were Norman Robert Pogson, Michael Topping and John Goldingham...

 of the East India Company
British East India Company
The East India Company was an early English joint-stock company that was formed initially for pursuing trade with the East Indies, but that ended up trading mainly with the Indian subcontinent and China...

 claimed that the orbit of the binary showed an anomaly, and it was "highly probable" that there was a "planetary body in connection with this system". T. J. J. See
Thomas Jefferson Jackson See
Thomas Jefferson Jackson See, was an American astronomer of high potential who ended a colorful life with no real accomplishment in astronomy or physics...

 made a stronger claim for the existence of a dark companion in this system in 1899, but Forest Ray Moulton
Forest Ray Moulton
Forest Ray Moulton was an American astronomer.He was born in Le Roy, Michigan, and was educated at Albion College. After graduating in 1894 , he performed his graduate studies at the University of Chicago and gained a Ph.D. in 1899...

 soon published a paper proving that a three-body system with the specified orbital parameters would be highly unstable. The claims by Jacob and See have both been shown to be erroneous. Jacob's claim was probably one of the first for an exoplanet based on astrometric
Astrometry
Astrometry is the branch of astronomy that involves precise measurements of the positions and movements of stars and other celestial bodies. The information obtained by astrometric measurements provides information on the kinematics and physical origin of our Solar System and our Galaxy, the Milky...

 evidence.

A claim of a planetary system was again made by Dirk Reuyl
Dirk Reuyl
Dirk Reuyl was a Dutch American physicist and astronomer. He was the cousin of astronomer Peter van de Kamp.-Life:He was awarded his Ph.D from Utrecht University in Utrecht, Netherlands. He came to the United States a few years before his cousin Peter van de Kamp. He joined the staff at McCormick...

 and Erik Holberg in 1943. The companion was estimated to have a mass one tenth the mass of the Sun
Sun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...

. This caused quite a sensation at the time but later observations have gradually discredited this claim.

Refining planetary boundaries

The negative results of past studies does not completely rule out the possibility of planets. In 2006 a McDonald Observatory
McDonald Observatory
The McDonald Observatory is an astronomical observatory located near the unincorporated community of Fort Davis in Jeff Davis County, Texas, United States. The facility is located on Mount Fowlkes and Mount Locke in the Davis Mountains of West Texas...

 team has set limits to the presence of one or more planets around 70 Ophiuchi with masses between 0.46 and 12.8 Jupiter masses and average separations spanning between 0.05 and 5.2 AU.

See also

  • Barnard's Star
    Barnard's star
    Barnard's Star, also known occasionally as Barnard's "Runaway" Star, is a very low-mass red dwarf star approximately six light-years away from Earth in the constellation of Ophiuchus . In 1916, the American astronomer E.E...

  • List of the nearest stars
  • 70 Ophiuchi in fiction

External links

  • Detection Limits from the McDonald Observatory Planet Search Program
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