Contents

70 Ophiuchi

70 Ophiuchi

Observation data Epoch J2000      Equinox
Constellation	Ophiuchus
70 Ophiuchi
Right ascension	18h05m 27.285s[1]
Declination	+02° 29′ 00.36″[1]
Apparent magnitude (V)	4.00 - 4.03[2]
A
Right ascension	18h05m 27.371s[3]
Declination	+02° 29′ 59.32″[3]
Apparent magnitude (V)	4.13[3]
B
Right ascension	18h05m 27.462s[4]
Declination	+02° 29′ 56.22″[4]
Apparent magnitude (V)	6.07[3]
Characteristics
Spectral type	K0V + K4V[5]
Apparent magnitude (B)	4.97/7.26[3]
Apparent magnitude (R)	3.6/5.6[3]
U−B color index	+0.69[6]
B−V color index	+0.84/+1.19[3]
Variable type	BY Dra[7]orRS CVn[2]
Astrometry
70 Oph A
Radial velocity (Rv)	−6.87[8] km/s
Proper motion (μ)	RA: 206.525±0.246[9] mas/yr Dec.: −1107.492±0.164[9] mas/yr
Parallax (π)	195.5674 ± 0.1964 mas[9]
Distance	16.68 ± 0.02 ly (5.113 ± 0.005 pc)
Absolute magnitude (MV)	+5.49[10]
70 Oph B
Proper motion (μ)	RA: 333.292±0.264[11] mas/yr Dec.: −1068.354±0.215[11] mas/yr
Parallax (π)	195.2166 ± 0.1012 mas[12]
Distance	16.707 ± 0.009 ly (5.123 ± 0.003 pc)
Orbit[8]
Period (P)	88.38±0.017 yr
Semi-major axis (a)	4.554±0.0052″
Eccentricity (e)	0.4992±0.00039
Inclination (i)	121.16±0.078°
Longitude of the node (Ω)	302.12±0.097°
Periastron epoch (T)	1895.94
Argument of periastron (ω) (secondary)	14.0±0.14°
Details
70 Oph A
Mass	0.90 ± 0.04[13] M☉
Radius	0.91 ± 0.03[14] R☉
Luminosity (bolometric)	0.59 ± 0.02[14] L☉
Surface gravity (log g)	4.5[15] cgs
Temperature	5,300[15] K
Metallicity [Fe/H]	+0.04[16] dex
Rotation	19.7 days[16]
Age	1.9[17] Gyr
70 Oph B
Mass	0.70 ± 0.07[13] M☉
Luminosity (bolometric)	0.13 ± 0.03[13] L☉
Temperature	4,350 ± 150[13] K
Other designations
p Ophiuchi, V2391 Ophiuchi, BD+02 3482, Gl 702, HD 165341, HIP 88601, HR 6752, PLX 4137
70 Oph A: LHS 458
70 Oph B: LHS 459
Database references
SIMBAD	The system
	A
	B
Exoplanet Archive	data
ARICNS	data
70 Location of 70 Ophiuchi in the constellation Ophiuchus

70 Ophiuchi is a binary star system located 16.6 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.

InPtolemy's 2nd-century Almagest star catalogue this star system is listed as a 4th magnitude star, the 28th (or4th outside the constellation figure) in Ophiuchus. It is star No. 261 in this catalogue.^[18]

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.^[19]

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 a BY Draconis variable^[7] or an RS Canum Venaticorum variable, and a period of 1.92396 days has been measured.^[2]

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.^[5] The two stars orbit each other at an average distance of 23.2 AU. But since the orbit is highly elliptical (ate=0.499), the separation between the two varies from 11.4 to 34.8 AU,^[21] with one orbit taking 88.38 years to complete.^[8]

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".^[22] 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.^[23]

T. J. J. See made a stronger claim for the existence of a dark companion in this system in 1899,^[24] but Forest Ray Moulton soon published a paper proving that a three-body system with the specified orbital parameters would be highly unstable.^[25] The claims by Jacob and See have both been shown to be erroneous.^[26]

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.^[27] 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.^[28] This caused quite a sensation at the time but later observations have gradually discredited this claim.^[26][29][30]

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.^[31]

• 61 Cygni
• Barnard's Star
• List of nearest stars and brown dwarfs

• Detection Limits from the McDonald Observatory Planet Search Program
• "70 Ophiuchi". SolStation. Retrieved October 24, 2005.