70 Ophiuchi

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70 Ophiuchi A
Stellar characteristics
Constellation	Ophiuchus
Right ascension (Epoch J2000)	18h 05m 27.29s
Declination (Epoch J2000)	+02° 30' 00.36"
Spectral type	K0-1 Ve
Distance from Sol	16.6 ly
Other designations	70 Oph, HR 6752, Gl 702 A, Hip 88601, HD 165341, SAO 123107, LHS 458, ADS 11046 A, Struve 2272 A

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70 Ophiuchi B
Stellar characteristics
Constellation	Ophiuchus
Right ascension (Epoch J2000)	18h 05m 27.29s
Declination (Epoch J2000)	+02° 30' 00.36"
Spectral type	K5-6 Ve
Distance from Sol	16.6 ly
Other designations	Gl 702 B, LHS 459, ADS 11046 B, Struve 2272 B

70 Ophiuchi is a binary, possibly trinary, system located approximately 16.6 light years from Sol. Stars A and B have a relatively wide separation. Previous estimates that AB are separated "on average" by 23.3 AUs in a highly eccentric orbit (e= 0.495) that swings between 11.7 and 34.8 AUs and takes 88.3 years to complete may have been revised slightly. Based on new measurements found in the new Sixth Catalog of Visual Orbits of Binary Stars, 70 Ophiuchi A and B may be separated on average by a semi-major axis of 23.2 AUs (4.554") in a highly elliptical orbit (e= 0.499) that takes 83.38 years to complete. The distance separating the two stars varies from 11.4 and 34.8 AUs; they are always separated from each other by roughly the orbital distance of Saturn in the Solar System. Lastly, the inclination of the orbit is 121.2° (revised from 120.8°), from the perspective of an observer on Earth.

70 Ophiuchi A

A main sequence orange-red dwarf (K0-1 Ve), the primary has only about 92 percent of Sol's mass, about 89 percent of its diameter (Johnson and Wright, 1983, page 691), 43 percent of its visual luminosity (51 percent with infrared adjustment), and from 30 to 100 percent of Sol's abundance of elements heavier than hydrogen ("metallicity"), based on its abundance of iron. On the other hand, residual dust left over from the star's infancy has been detected in the binary system, as has been found in the Solar System.

The orbital distance where an Earth-type planet would have liquid water is centered around 0.68 AU -- near the Venus-Sun distance in the Solar System -- where a planet's period would be about 228 days or almost two thirds of an Earth year. 70 Ophiuchi A has the variable star designation V2391.

70 Ophiuchi B

A main sequence orange-red dwarf (K5-6 Ve), star B has only about 70 percent of Sol's mass, about 73 percent of its diameter, and 8.4 to nine percent of its visual luminosity (16 percent with infrared adjustment). The orbital distance where an Earth-type planet would have liquid water is centered around 0.30 AU -- three fourths of Mercury's orbital distance in the Solar System -- where the orbital period would be over 77 days.

Trinary System?

Over the past two centuries, many investigators of the visual orbits of this well-known binary system have found evidence for a third body of fairly low mass perturbing the motion of one or other of the two visible components. According to Robert Burnham, Jr., the earliest observers who found that 70 Ophiuchi showed clear deviations in Keplerian motion included: J. H. Madler (1842), W.S. Jacob (1855), T.J.J. See (1896), and E. Doolittle (1897), and T. Lewis (1906). However, those and subsequent observers failed to agree on the orbital period or amplitude of the perturbation, or even on which of the two stars was disturbed in its motion. In 1937, Kaj Aage Gunnar Strand (1907-2000) -- who later became scientific director of the U.S. Naval Observatory -- found no evidence for a third body, but in 1943, Dirk Reuyl and Erik Holberg found indications of a 17-year perturbation from a body with about 10 times Jupiter's mass using astrometic plates made at McCormick Observatory between 1914 and 1943. Most recently, however, Batten et al (1984) and Heintz (1988) have found no evidence supporting detectable perturbations.

(Information from SolStation.com)