# 70 Ophiuchi

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70 Ophiuchi
Observation data
Epoch J2000      Equinox
Constellation Ophiuchus
70 Oph A[1]
Right ascension 18h 05m 27.371s[1]
Declination +02° 29′ 59.32″[1]
Apparent magnitude (V) 4.123[1]
70 Oph B[2]
Right ascension 18h 05m 27.421s[2]
Declination +02° 29′ 56.42″[2]
Apparent magnitude (V) 6.17[2]
Characteristics
Spectral type K0V[1] + K4V[2]
Apparent magnitude (B) 4.97[1]/~7.15[2]
Apparent magnitude (V) 4.123[1]/~6.00[2]
Apparent magnitude (R) ~3.6[1]/~5.6[2]
U−B color index 0.51[3]
B−V color index 0.777[1]/-
Variable type BY[4]
Astrometry
Radial velocity (Rv) -6.9 km/s
Proper motion (μ) RA: 124.16[5] mas/yr
Dec.: -962.82 mas/yr
Parallax (π) 196.72 ± 0.83[5] mas
Distance 16.58 ± 0.07 ly
(5.08 ± 0.02 pc)
Absolute magnitude (MV) 5.49[6]/7.47
Orbit[7]
Primary 70 Oph A
Companion 70 Oph B
Period (P) 88.3 yr
Semi-major axis (a) 4.56″
Eccentricity (e) 0.495
Inclination (i) 120.8°
Longitude of the node (Ω) 301.4°
Periastron epoch (T) 1984.3
Argument of periastron (ω)
(secondary)
13.2°
Details
70 Oph A
Mass 0.90 ± 0.04[8] M
Radius 0.91 ± 0.03[9] R
Luminosity (bolometric) 0.59 ± 0.02[9] L
Luminosity (visual, LV) 0.54[note 1] L
Surface gravity (log g) 4.5[10] cgs
Temperature 5,300[10] K
Metallicity 102% ± 1[8] Z
Metallicity [Fe/H] +0.04[11] dex
Rotation 19.7 days[11]
Age 1.9[12] Gyr
70 Oph B
Mass 0.70 ± 0.07[8] M
Radius ~0.65 R
Luminosity (bolometric) 0.13 ± 0.03[8] L
Luminosity (visual, LV) ~0.09 L
Temperature 4,350 ± 150[8] K
Other designations
70 Oph A
BD+02° 3482A, GCTP 4137.00, Gl 702 A, HD 165341A, HIP 88601A, HR 6752, LHS 458.

70 Oph B

BD+02° 3482B, Gl 702 B, HD 165341B, HIP 88601B, LFT 1391, LHS 459, LTT 15338, NLTT 45900.
Database references
SIMBAD The system
A
B
Exoplanet Archive data
ARICNS data

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.[3]

## Binary star

The primary star is a yellow-orange main sequence dwarf of spectral type K0,[1] the secondary star is an orange main sequence dwarf of spectral type K4[2] and is a suspected variable star that may be the cause of variations that make the binary BY Draconis variable.[4] The two stars orbit each other at an average distance of 23.2 AUs. But since the orbit is highly elliptical (at e=0.499), the separation between the two varies from 11.4 to 34.8 AUs, with one orbit taking 83.38 years to complete.[13]

## History

This star system was first cataloged 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. He commented at the time that there was a possible third unseen companion affecting the orbit of the two visible stars.[14]

## Claims of a planetary system

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".[15] This is the first attempt to use radial velocity to detect an exoplanet, and the first based on astrometric evidence.[16]

T. J. J. See made a stronger claim for the existence of a dark companion in this system in 1899,[14] but Forest Ray Moulton soon published a paper proving that a three-body system with the specified orbital parameters would be highly unstable.[17] The claims by Jacob and See have both been shown to be erroneous.[18]

A claim of a planetary system was again made by Dirk Reuyl and Erik Holberg in 1943. The companion was estimated to have a mass one tenth the mass of the Sun.[19] This caused quite a sensation at the time but later observations have gradually discredited this claim.[18]

### Refining planetary boundaries

The negative results of past studies does not completely rule out the possibility of planets. In 2006 a McDonald Observatory team has 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.[20]

## References

1. "* 70 Oph A". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2018-03-08.
2. "* 70 Oph B". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2009-06-04.
3. ^ a b "* 70 Oph". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2009-06-04.
4. ^ a b "GCVS Query= V2391 Oph". General Catalog of Variable Stars. Sternberg Astronomical Institute, Moscow, Russia. Retrieved 2018-03-08.
5. ^ a b van Leeuwen, F. (November 2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics, 474 (2): 653–664, arXiv:, Bibcode:2007A&A...474..653V, doi:10.1051/0004-6361:20078357
6. ^ Holmberg, J.; et al. (July 2009), "The Geneva-Copenhagen survey of the solar neighbourhood. III. Improved distances, ages, and kinematics", Astronomy and Astrophysics, 501 (3): 941–947, arXiv:, Bibcode:2009A&A...501..941H, doi:10.1051/0004-6361/200811191.
7. ^ Heintz, W. D. (1988), "The binary star 70 Ophiuchi revisited", Journal of the Royal Astronomical Society of Canada, 82: 140, Bibcode:1988JRASC..82..140H
8. Fernandes, J.; Lebreton, Y.; Baglin, A.; Morel, P. (1998), "Fundamental stellar parameters for nearby visual binary stars: eta Cas, XI Boo, 70 OPH and 85 Peg", Astronomy and Astrophysics, 338: 455–464, Bibcode:1998A&A...338..455F
9. ^ a b Bruntt, H.; et al. (July 2010), "Accurate fundamental parameters for 23 bright solar-type stars", Monthly Notices of the Royal Astronomical Society, 405 (3): 1907–1923, arXiv:, Bibcode:2010MNRAS.405.1907B, doi:10.1111/j.1365-2966.2010.16575.x
10. ^ a b 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
11. ^ a b Maldonado, J.; et al. (October 2010), "A spectroscopy study of nearby late-type stars, possible members of stellar kinematic groups", Astronomy and Astrophysics, 521: A12, arXiv:, Bibcode:2010A&A...521A..12M, doi:10.1051/0004-6361/201014948
12. ^ Mamajek, Eric E.; Hillenbrand, Lynne A. (November 2008), "Improved Age Estimation for Solar-Type Dwarfs Using Activity-Rotation Diagnostics", The Astrophysical Journal, 687 (2): 1264–1293, arXiv:, Bibcode:2008ApJ...687.1264M, doi:10.1086/591785
13. ^ Solstation article giving details of orbital mechanics of the system
14. ^ a b See, Thomas Jefferson Jackson (1896). "Researches on the Orbit of F.70 Ophiuchi, and on a Periodic Perturbation in the Motion of the System Arising from the Action of an Unseen Body". The Astronomical Journal. 16: 17. Bibcode:1896AJ.....16...17S. doi:10.1086/102368.
15. ^ Jacob, W.S. (1855). "On Certain Anomalies presented by the Binary Star 70 Ophiuchi". Monthly Notices of the Royal Astronomical Society. Blackwell Scientific Publications, for the Royal Astronomical Society. 15 (9): 228–230. Bibcode:1855MNRAS..15..228J. doi:10.1093/mnras/15.9.228.
16. ^ https://www.youtube.com/watch?v=2hNWCI-9n8Q
17. ^ Sherrill, Thomas J. (1999). "A Career of controversy: the anomaly OF T. J. J. See" (PDF). Journal for the History of Astronomy. 30: 25–50. Bibcode:1999JHA....30...25S. doi:10.1177/002182869903000102. Archived (PDF) from the original on 25 September 2007. Retrieved 2007-08-27.
18. ^ a b Heintz, W.D. (June 1988). "The Binary Star 70 Ophiuchi Revisited" (PDF). Journal of the Royal Astronomical Society of Canada. 82 (3): 140. Bibcode:1988JRASC..82..140H.
19. ^ Reuyl, Dirk; Holmberg, Erik (January 1943). "On the Existence of a Third Component in the System 70 Ophiuchi" (PDF). The Astrophysical Journal. 97: 41–46. Bibcode:1943ApJ....97...41R. doi:10.1086/144489.
20. ^ Wittenmyer; Endl, Michael; Cochran, William D.; Hatzes, Artie P.; Walker, G. A. H.; Yang, S. L. S.; Paulson, Diane B. (7 April 2006). "Detection Limits from the McDonald Observatory Planet Search Program" (PDF). The Astronomical Journal. 132 (1): 177–188. arXiv:. Bibcode:2006AJ....132..177W. doi:10.1086/504942.

## Notes

1. ^ Taking the absolute visual magnitude of 70 Ophiuchi A ${\displaystyle \scriptstyle M_{V_{\ast }}=5.5}$ and the absolute visual magnitude of the Sun ${\displaystyle \scriptstyle M_{V_{\odot }}=4.83}$, the visual luminosity can be calculated by ${\displaystyle \scriptstyle {\frac {L_{V_{\ast }}}{L_{V_{\odot }}}}=10^{0.4\left(M_{V_{\odot }}-M_{V_{\ast }}\right)}}$