Epoch J2000 Equinox
|70 Oph A|
|Right ascension||18h 05m 27.371s|
|Declination||+02° 29′ 59.32″|
|Apparent magnitude (V)||4.03|
|70 Oph B|
|Right ascension||18h 05m 27.421s|
|Declination||+02° 29′ 56.42″|
|Apparent magnitude (V)||6.00|
|Spectral type||K0V + K4V|
|Apparent magnitude (B)||~4.89/~7.15|
|Apparent magnitude (V)||~4.03/~6.00|
|Apparent magnitude (R)||-/~5.6|
|U−B color index||0.57/-|
|B−V color index||0.85/-|
|Radial velocity (Rv)||-6.9 km/s|
|Proper motion (μ)||RA: 124.16 mas/yr
Dec.: -962.82 mas/yr
|Parallax (π)||196.72 ± 0.83 mas|
|Distance||16.58 ± 0.07 ly
(5.08 ± 0.02 pc)
|Absolute magnitude (MV)||5.5/7.47|
|Companion||70 Oph B|
|Period (P)||88.3 yr|
|Semi-major axis (a)||4.56"|
|Longitude of the node (Ω)||301.4°|
|Periastron epoch (T)||1984.3|
|Argument of periastron (ω)
|70 Oph A|
|Mass||0.90 ± 0.04 M☉|
|Radius||0.91 ± 0.03 R☉|
|Luminosity (bolometric)||0.59 ± 0.02 L☉|
|Luminosity (visual, LV)||0.54[note 1] L☉|
|Surface gravity (log g)||4.5 cgs|
|Metallicity||100% ± 25 Z☉|
|Metallicity [Fe/H]||+0.04 dex|
|70 Oph B|
|Mass||0.70 ± 0.07 M☉|
|Luminosity (bolometric)||0.13 ± 0.03 L☉|
|Luminosity (visual, LV)||~0.09 L☉|
|Temperature||4,350 ± 150 K|
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.
The primary star is a yellow-orange main sequence dwarf BY Draconis variable of spectral type K0, and the secondary star is an orange main sequence dwarf of spectral type K4. 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.
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.
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". T. J. J. See made a stronger claim for the existence of a dark companion in this system in 1899, but Forest Ray Moulton soon published a paper proving that a three-body system with the specified orbital parameters would be highly unstable. The claims by Jacob and See have both been shown to be erroneous. 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. This caused quite a sensation at the time but later observations have gradually discredited this claim.
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.
- "SIMBAD query result: V* V2391 Oph -- Spectroscopic binary". Centre de Données astronomiques de Strasbourg. Retrieved 2009-06-04.
- "SIMBAD query result: LHS 459 -- High proper-motion Star". Centre de Données astronomiques de Strasbourg. Retrieved 2009-06-04.
- "GCVS Query= V2391 Oph". General Catalog of Variable Stars. Sternberg Astronomical Institute, Moscow, Russia. Retrieved 2009-06-04.
- 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
- Heintz, W. D. (1988), "The binary star 70 Ophiuchi revisited", Journal of the Royal Astronomical Society of Canada, Bibcode:1988JRASC..82..140H
- 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
- 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
- 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
- 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
- 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
- Solstation article giving details of orbital mechanics of the system
- 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.
- 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: 228–230. Bibcode:1855MNRAS..15..228J. doi:10.1093/mnras/15.9.228.
- 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.
- 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.
- 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.
- 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.
- Taking the absolute visual magnitude of 70 Ophiuchi A and the absolute visual magnitude of the Sun , the visual luminosity can be calculated by
- Detection Limits from the McDonald Observatory Planet Search Program
- "70 Ophiuchi". SolStation. Retrieved October 24, 2005.