70 Ophiuchi is a binary

star system 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 speakin ...

located 16.6

light year A light-year, alternatively spelled light year, is a large unit of length used to express astronomical distances and is equivalent to about 9.46 trillion kilometers (), or 5.88 trillion miles ().One trillion here is taken to be 1012 ...

s away from the

Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surf ...

. It is in the constellation

Ophiuchus Ophiuchus () is a large constellation straddling the celestial equator. Its name comes from the Ancient Greek (), meaning "serpent-bearer", and it is commonly represented as a man grasping a snake. The serpent is represented by the constell ...

. At magnitude 4 it appears as a dim star visible to the unaided eye away from city lights.

History

In the

Ptolemy Claudius Ptolemy (; grc-gre, Πτολεμαῖος, ; la, Claudius Ptolemaeus; AD) was a mathematician, astronomer, astrologer, geographer, and music theorist, who wrote about a dozen scientific treatises, three of which were of import ...

's 2nd-century

Almagest The ''Almagest'' is a 2nd-century Greek-language mathematical and astronomical treatise on the apparent motions of the stars and planetary paths, written by Claudius Ptolemy ( ). One of the most influential scientific texts in history, it cano ...

star catalogue this star system is listed as a 4th magnitude star, the ''28th'' (or ''4th outside the constellation figure'') in ''Ophiuchus''. It is star ''No. 261'' in this catalogue. This star system was first catalogued as a binary star by

William Herschel Frederick William Herschel (; german: Friedrich Wilhelm Herschel; 15 November 1738 – 25 August 1822) was a German-born British astronomer and composer. He frequently collaborated with his younger sister and fellow astronomer Carolin ...

in the late 18th century in his study of binary stars. Herschel proved that this system is a gravitationally bound binary system where the two stars orbit around a common center of mass. This was an important contribution to the proof that

Newton's law of universal gravitation Newton's law of universal gravitation is usually stated as that every particle attracts every other particle in the universe with a force that is proportional to the product of their masses and inversely proportional to the square of the distanc ...

applied to objects beyond the

Solar System The Solar System Capitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all individual astronomical objects but uses mixed "Solar ...

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

Variability

70 Ophiuchi is a variable star with a magnitude range for the two stars combined of 4.00 to 4.03. The type of variability is uncertain and it is not clear which of the two components causes the variations. It has been suspected of being either a BY Draconis variable or an RS Canum Venaticorum variable, and a period of 1.92396 days has been measured.

Binary star

The primary star is a yellow-orange

main sequence In astronomy, 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 Her ...

dwarf of

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 th ...

K0, while the secondary is an orange dwarf of

K4. The two stars orbit each other at an average distance of 23.2 AU. But since the orbit is highly elliptical (at ''e''=0.499), the separation between the two varies from 11.4 to 34.8 AU, with one orbit taking 88.38 years to complete.

Claims of a planetary system

In 1855,

William Stephen Jacob William Stephen Jacob (1813–1862) was an English immigrant astronomer in India, who acted as the director of the Madras Observatory from 1848 to 1859. His early claim of 1855 to have detected an exoplanet, in orbit around 70 Ophiuchi, is now tho ...

of the Madras Observatory 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". This is the first known attempt to use

astrometric 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. Histor ...

methods to detect an

exoplanet 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 ...

, although

Friedrich Bessel Friedrich Wilhelm Bessel (; 22 July 1784 – 17 March 1846) was a German astronomer, mathematician, physicist, and geodesist. He was the first astronomer who determined reliable values for the distance from the sun to another star by the met ...

had applied similar methods 10 years earlier to deduce the existence of

Sirius B Sirius is the brightest star in the night sky. Its name is derived from the Greek word , or , meaning 'glowing' or 'scorching'. The star is designated α Canis Majoris, Latinized to Alpha Canis Majoris, and abbreviated Alpha CM ...

. T. J. J. See made a stronger claim for the existence of a dark companion in this system in 1899, but Forest Ray Moulton 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. Discovery of a "third dark companion" was announced by Louis Berman in 1932. This "dark body" around 70 Oph A was thought to have an 18-year period and a mass of 0.1 to 0.2 the Sun's mass. A claim of a planetary system was again made, this time by Dirk Reuyl and Erik Holberg in 1943. The companion was estimated to have a mass 0.008 to 0.012 that of the Sun and a 17-year period. This caused quite a sensation at the time but later observations have gradually discredited this claim. The negative results of past studies does not completely rule out the possibility of planets. In 2006 a

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 ...

team 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.

References

External links