# 70 Ophiuchi

(Redirected from 70 Oph)
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) 4.03[1]
70 Oph B[2]
Right ascension 18h 05m 27.421s[2]
Declination +02° 29′ 56.42″[2]
Apparent magnitude (V) 6.00[2]
Characteristics
Spectral type K0V[1] + K4V[2]
Apparent magnitude (B) ~4.89[1]/~7.15[2]
Apparent magnitude (V) ~4.03[1]/~6.00[2]
Apparent magnitude (R) -/~5.6[2]
U−B color index 0.57/-
B−V color index 0.78/-
Variable type BY[3]/-
Astrometry
Radial velocity (Rv) -6.9 km/s
Proper motion (μ) RA: 124.16[4] mas/yr
Dec.: -962.82 mas/yr
Parallax (π) 196.72 ± 0.83[4] mas
Distance 16.58 ± 0.07 ly
(5.08 ± 0.02 pc)
Absolute magnitude (MV) 5.5/7.47
Orbit[5]
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[6] M
Radius 0.91 ± 0.03[7] R
Luminosity (bolometric) 0.59 ± 0.02[7] L
Luminosity (visual, LV) 0.54[note 1] L
Surface gravity (log g) 4.5[8] cgs
Temperature 5,300[8] K
Metallicity 100% ± 25[6] Z
Metallicity [Fe/H] +0.04[9] dex
Rotation 19.7 days[9]
Age 1.9[10] Gyr
70 Oph B
Mass 0.70 ± 0.07[6] M
Luminosity (bolometric) 0.13 ± 0.03[6] L
Luminosity (visual, LV) ~0.09 L
Temperature 4,350 ± 150[6] K
Other designations
70 Oph A
BD +02°3482A, GCTP 4137.00, GJ 702 A, HD 165341A, HIP 88601A, HR 6752, LHS 458.

70 Oph B

BD +02°3482B, GJ 702 B, HD 165341B, HIP 88601B, LFT 1391, LHS 459, LTT 15338, NLTT 45900.
Database references
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.[1]

## Binary star

The primary star is a yellow-orange main sequence dwarf BY Draconis variable[3] of spectral type K0, and the secondary star is an orange main sequence dwarf of spectral type K4.[2] 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.[11]

## 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 as a gravitationally bound binary system where the two stars orbited 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.[12]

## Distance

70 Ophiuchi distance estimates

Source Parallax, mas Distance, pc Distance, ly Distance, Pm Ref.
Woolley et al. (1970) 195 ± 5 5.13 ± 0.13 16.7 ± 0.4 158.2+4.2
−4
[13]
Gliese & Jahreiß (1991) 199.0 ± 3.6 5.03 ± 0.09 16.39+0.3
−0.29
155.1+2.9
−2.8
[14]
van Altena et al. (1995) 199.7 ± 3.4 5.01+0.09
−0.08
16.33+0.28
−0.27
154.5+2.7
−2.6
[15]
Perryman et al. (1997) (Hipparcos) 196.62 ± 1.38 5.09 ± 0.04 16.59 ± 0.12 156.9 ± 1.1 [16]
Perryman et al. (1997) (Tycho) (absents) [17]
Söderhjelm (1999) 195.7 ± 0.9 5.11+0.024
−0.023
16.67 ± 0.08 157.7 ± 0.7 [18]
van Leeuwen (2007) 196.72 ± 0.83 5.083+0.022
−0.021
16.58 ± 0.07 156.9 ± 0.7 [19]
RECONS TOP100 (2012) 195.96 ± 0.87[note 2] 5.103 ± 0.023 16.64 ± 0.07 157.5 ± 0.7 [20]

Non-trigonometric distance estimates are marked in italic. The most precise estimate is marked in bold.

## Claims of a planetary system

In 1855, Capt. W. S. Jacob of the Madras Observatory of the East India Company 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] T. J. J. See made a stronger claim for the existence of a dark companion in this system in 1899,[12] but Forest Ray Moulton soon published a paper proving that a three-body system with the specified orbital parameters would be highly unstable.[22] The claims by Jacob and See have both been shown to be erroneous.[23] Jacob's claim was probably one of the first for an exoplanet based on astrometric evidence.
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.[24] This caused quite a sensation at the time but later observations have gradually discredited this claim.[23]

### 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.[25]

## References

1. ^ a b "GCVS Query= V2391 Oph". General Catalog of Variable Stars. Sternberg Astronomical Institute, Moscow, Russia. Retrieved 2009-06-04.
2. ^ a b van Leeuwen, F. (November 2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics 474 (2): 653–664, arXiv:0708.1752, Bibcode:2007A&A...474..653V, doi:10.1051/0004-6361:20078357
3. ^ Heintz, W. D. (1988), "The binary star 70 Ophiuchi revisited", Royal Astronomical Society of Canada, Journal, Bibcode:1988JRASC..82..140H
4. 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
5. ^ 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:1002.4268, Bibcode:2010MNRAS.405.1907B, doi:10.1111/j.1365-2966.2010.16575.x
6. ^ 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
7. ^ 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:1007.1132, Bibcode:2010A&A...521A..12M, doi:10.1051/0004-6361/201014948
8. ^ 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:0807.1686, Bibcode:2008ApJ...687.1264M, doi:10.1086/591785
9. ^ Solstation article giving details of orbital mechanics of the system
10. ^ 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.
11. ^ Woolley R.; Epps E. A.; Penston M. J.; Pocock S. B. (1970). "Woolley 702". Catalogue of stars within 25 parsecs of the Sun. Retrieved 2014-11-21.
12. ^ Gliese, W. and Jahreiß, H. (1991). "Gl 702". Preliminary Version of the Third Catalogue of Nearby Stars. Retrieved 2014-11-21.
13. ^ Van Altena W. F., Lee J. T., Hoffleit E. D. (1995). "GCTP 4137". The General Catalogue of Trigonometric Stellar Parallaxes (Fourth ed.). Retrieved 2014-11-21.
14. ^ Perryman et al. (1997). "HIP 88601". The Hipparcos and Tycho Catalogues. Retrieved 2014-11-21.
15. ^ Perryman et al. (1997). "HIP 88601". The Hipparcos and Tycho Catalogues. Retrieved 2014-11-21.
16. ^ Söderhjelm, Staffan (1999). "HIP 88601". Visual binary orbits and masses post Hipparcos. Retrieved 2014-10-21.
17. ^ van Leeuwen F. (2007). "HIP 88601". Validation of the new Hipparcos reduction. Retrieved 2014-11-21.
18. ^ "RECONS TOP100". THE ONE HUNDRED NEAREST STAR SYSTEMS brought to you by RECONS (Research Consortium On Nearby Stars). 2012. Retrieved 2014-11-21.
19. ^ 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: 228. Bibcode:1855MNRAS..15..228J.
20. ^ Sherrill, Thomas J. (1999). "A Career of controversy: the anomaly OF T. J. J. See" (PDF). Journal for the history of astronomy 30. Archived (PDF) from the original on 25 September 2007. Retrieved 2007-08-27.
21. ^ a b Heintz, W.D. (June 1988). "The Binary Star 70 Ophiuchi Revisited" (PDF). Journal of the Royal Astronomical Society of Canada 82 (3). Bibcode:1988JRASC..82..140H.
22. ^ 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.
23. ^ 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:astro-ph/0604171. Bibcode:2006AJ....132..177W. doi:10.1086/504942.

## Notes

1. ^ Taking the absolute visual magnitude of 70 Ophiuchi A $\scriptstyle M_{V_{\ast}}=5.5$ and the absolute visual magnitude of the Sun $\scriptstyle M_{V_{\odot}}=4.83$, the visual luminosity can be calculated by $\scriptstyle \frac{L_{V_{\ast}}}{L_{V_{\odot}}}=10^{0.4\left(M_{V_{\odot}} - M_{V_{\ast}}\right)}$
2. ^ Weighted parallax based on parallaxes from van Altena et al. (1995) and Söderhjelm (1999).