70 Ophiuchi
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70 Ophiuchi (p Ophiuchi)<ref name="Gore1888"/> is a binary star system located 16.7 light-years away from the Earth. It is in the constellation Ophiuchus. At magnitude 4 it appears as a dim star visible to the unaided eye away from city lights.
HistoryEdit
In Ptolemy's 2nd-century Almagest 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.<ref name=vizier/>
This star system was first catalogued as a binary star by William Herschel 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 applied to objects beyond the Solar System.
This star was once considered part of the obsolete constellation Taurus Poniatovii, but after the International Astronomical Union officially recognized constellations, it was placed in Ophiuchus.<ref name=ridpath/>
VariabilityEdit
70 Ophiuchi is a variable star with a magnitude range for the two stars combined of 4.00 to 4.03.<ref name=vsx/> 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<ref name=gcvs/> or an RS Canum Venaticorum variable, and a period of 1.92396 days has been measured.<ref name=vsx/>
Binary starEdit
The primary star is a yellow-orange main sequence dwarf of spectral type K0, while the secondary is an orange dwarf of spectral type K4.<ref name=mk/> 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,<ref name=solstation/> with one orbit taking 88.38 years to complete.<ref name=pourbaix/>
Claims of a planetary systemEdit
In 1855, William Stephen Jacob 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".<ref name=Jacob/> This is the first known attempt to use astrometric methods to detect an exoplanet, although Friedrich Bessel had applied similar methods 10 years earlier to deduce the existence of Sirius B.<ref name="Kipping"/>
T. J. J. See made a stronger claim for the existence of a dark companion in this system in 1899,<ref name="See"/> but Forest Ray Moulton soon published a paper proving that a three-body system with the specified orbital parameters would be highly unstable.<ref name=JHA/> The claims by Jacob and See have both been shown to be erroneous.<ref name="heintz1988"/>
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.<ref name=LOB/> 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.<ref name=OETCS70O/> This caused quite a sensation at the time but later observations have gradually discredited this claim.<ref name="heintz1988"/><ref name=SNT5P/><ref name=POMBS70O/>
The negative results of past studies does not completely rule out the possibility of planets. In 2006 a McDonald Observatory 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.<ref name=search/>
See alsoEdit
ReferencesEdit
External linksEdit
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