70 Ophiuchi 2?

© Torben Krogh & Mogens Winther,

(Amtsgymnasiet and EUC Syd Gallery,
student photo used with permission)

70 Ophiuchi A and B are orange-red
dwarf stars, like Epsilon Eridani at
left center of meteor. (See a
Digitized Sky Survey field image
of 70 Ophiuchi from the
Nearby Stars Database.)

System Summary

This system is located about 16.6 light-years away in the northeastern part (18:05:27.29+02:30:00.36, ICRS 2000.0) of Constellation Ophiuchus, the Serpent Holder -- east of Gamma Ophiuchi. Sir William Friedrich Wilhelm Herschel (1738-1822, portrait) observed the system's two known stars in August 1779 but credited Father Christian Mayer (1719-1783) as having recognized its duplicity even earlier. Mayer had claimed to have discovered that many of the more conspicuous stars in the southern heavens were surrounded by smaller stars, of which one such observation was recorded in "Tables d'Aberration et de Mutation" (Mannheim, 1778), but virtually all of which could not be confirmed by contemporaries such as Herschel.

70 Ophiuchi A

A main sequence orange-red dwarf (K0-1 Ve), the primary has only about 92 percent of Sol's mass (RECONS), 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 (Caryrel de Strobel et al, 1991; page 302). 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 (Kuchner et al, 1998, in pdf).

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 Oph. Some useful star catalogue numbers include: 70 Oph, HR 6752, Gl 702 A, Hip 88601, HD 165341, SAO 123107, LHS 458, ADS 11046 A, and Struve 2272 A.

Stars A and B have a relatively wide separation. Previous estimates that AB are separated "on average" by 23.3 AUs (4.560" of a semi-major axis with a parallax of 0.19596 RECONS; 1/2000 table for Gl 702) in a highly eccentric orbit (e= 0.495) that swings between 11.7 and 34.8 AUs and takes 88.3 years to complete (Wulff Dieter Heintz, 1988; Batten and Fletcher, 1991; and D.J. Barlow, 1994) may have been revised slighly. Based on new measurements (Dimitri Pourbaix, 2000) 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. (See an animation of the orbits of Stars A and B and their potentially habitable zones, with a table of basic orbital and physical characteristics.)

70 Ophiuchi B

A main sequence orange-red dwarf (K5-6 Ve), star B has only about 70 percent of Sol's mass (RECONS), about 73 percent of its diameter (Johnson and Wright, 1983, page 691), 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. Some useful star catalogue numbers include: Gl 702 B, LHS 459, ADS 11046 B, and Struve 2272 B.

70 Ophiuchi Ab or Bb?

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.

Closest Neighbors

The following star systems are located within 10 ly of 70 Ophiuchi.

Star System	Spectra & Luminosity	Distance (light-years)
Ross 652 A Van Biesbroeck's	M3.5 Ve M8 Ve	6.1
Hip 85605	?	6.7
Wolf 630 A-C	M2.5 Ve M4.5 Ve M7 V	6.7
Altair	A7 V-IV	7.8
BD-12 4523 AB	M3.0 V ?	7.9
Wolf 629 AB	M3.5 V ?	8.2
BD-03 4233	M0 V	9.1
BD+02 3312	K7 V	9.3
Ross 154	M3.5-6 Ve	9.3
G 154-44	M4.5 V	9.9

Other Information

Try Professor Jim Kaler's Stars site for other information about 70 Ophiuchi at the University of Illinois' Department of Astronomy.

Up-to-date technical summaries on individual stars can be found at: the Astronomiches Rechen-Institut at Heidelberg's ARICNS for Star A and Star B, the Nearby Stars Database, and the Research Consortium on Nearby Stars (RECONS) list of the 100 Nearest Star Systems. Additional information may be available at Roger Wilcox's Internet Stellar Database.

One story is that the Ancient Greeks named this constellation after Aesculapius (the first doctor, a son of Apollo and Coronis, and grandfather of Hippocrates, the famous Greek physician). Aesculapius was killed by Zeus at the urging of Hades for threatening to make mankind immortal like the gods by bringing the dead back to life. In admiration of the doctor's skills, however, Zeus raised the doctor and the serpent from which he had first learned the medicinal usefulness of certain herbs into the heavens. Located along the equatorial region of the sky, Ophiuchus is one of the larger constellations. For more information and an illustration of the constellation, go to Christine Kronberg's Ophiuchus. For another illustration, see David Haworth's Ophiuchus.

For more information about stars including spectral and luminosity class codes, go to ChView's webpage on The Stars of the Milky Way.