InPtolemy's 2nd-centuryAlmagest star catalogue this star system is listed as a 4th magnitude star, the28th (or4th outside the constellation figure) inOphiuchus. It is starNo. 261 in this catalogue.[17]
This star system was first catalogued as a binary star byWilliam Herschel in the late 18th century in his study of binary stars. Herschel proved that this system is a gravitationally boundbinary system where the two stars orbit around a commoncenter of mass. This was an important contribution to the proof thatNewton's law of universal gravitation applied to objects beyond theSolar System.
70 Ophiuchi is a variable star with a magnitude range for the two stars combined of 4.00 to 4.03.[2] 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 aBY Draconis variable[8] or anRS Canum Venaticorum variable, and a period of 1.92396 days has been measured.[2]
The primary star is a yellow-orangemain sequence dwarf ofspectral type K0, while the secondary is an orange dwarf ofspectral type K4.[5] The two stars orbit each other at an average distance of 23.2AU. But since the orbit is highly elliptical (ate=0.499), the separation between the two varies from 11.4 to 34.8 AU,[20] with one orbit taking 88.38 years to complete.[9]
In 1855,William Stephen Jacob of theMadras 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".[21] This is the first known attempt to useastrometric methods to detect anexoplanet, althoughFriedrich Bessel had applied similar methods 10 years earlier to deduce the existence ofSirius B.[22]
T. J. J. See made a stronger claim for the existence of a dark companion in this system in 1899,[23] butForest Ray Moulton soon published a paper proving that a three-body system with the specified orbital parameters would be highly unstable.[24] The claims by Jacob and See have both been shown to be erroneous.[25]
Discovery of a "third dark companion" was announced byLouis 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 theSun's mass.[26] A claim of a planetary system was again made, this time byDirk Reuyl andErik Holberg in 1943. The companion was estimated to have a mass 0.008 to 0.012 that of theSun and a 17-year period.[27] This caused quite a sensation at the time but later observations have gradually discredited this claim.[25][28][29]
The negative results of past studies does not completely rule out the possibility of planets. In 2006 aMcDonald Observatory team set limits to the presence of one or more planets around 70 Ophiuchi with masses between 0.46 and 12.8Jupiter masses and average separations spanning between 0.05 and 5.2AU.[30]
^Ducati, J. R. (2002). "VizieR Online Data Catalog: Catalogue of Stellar Photometry in Johnson's 11-color system".VizieR On-line Data Catalog.2237.Bibcode:2002yCat.2237....0D.
^abcdefgEggenberger, P.; Miglio, A.; Carrier, F.; Fernandes, J.; Santos, N. C. (2008-05-01). "Analysis of 70 Ophiuchi AB including seismic constraints".Astronomy & Astrophysics.482 (2):631–638.arXiv:0802.3576.doi:10.1051/0004-6361:20078624.ISSN0004-6361.
^abcdefBoyajian, Tabetha S.; von Braun, Kaspar; van Belle, Gerard; McAlister, Harold A.; Brummelaar, Theo A. ten; Kane, Stephen R.; Muirhead, Phil; Jones, Jeremy; White, Russel; Schaefer, Gail; Ciardi, David; Henry, Todd; López-Morales, Mercedes; Ridgway, Stephen; Gies, Douglas (2012-10-01). "Stellar Diameters and Temperatures II. Main Sequence K & M Stars".The Astrophysical Journal.757 (2): 112.arXiv:1208.2431.doi:10.1088/0004-637X/757/2/112.ISSN0004-637X.
^Morell, O.; Kallander, D.; Butcher, H. R. (1999). "The age of the Galaxy from thorium in G dwarfs, a re-analysis".Astronomy and Astrophysics.259 (2):543–548.Bibcode:1992A&A...259..543M.
