70 Ophiuchi

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.

70 Ophiuchi
Observation data
Epoch J2000      Equinox
Constellation Ophiuchus
70 Ophiuchi
Right ascension 18h 05m 27.285s[1]
Declination +02° 29′ 00.36″[1]
Apparent magnitude (V) 4.00 - 4.03[2]
A
Right ascension 18h 05m 27.371s[3]
Declination +02° 29′ 59.32″[3]
Apparent magnitude (V) 4.13[3]
B
Right ascension 18h 05m 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] or RS Cvn[2]
Astrometry
Radial velocity (Rv)−6.87[8] km/s
Proper motion (μ) RA: 124.16[1] mas/yr
Dec.: −962.82[1] mas/yr
Parallax (π)196.72 ± 0.83[1] mas
Distance16.58 ± 0.07 ly
(5.08 ± 0.02 pc)
Absolute magnitude (MV)+5.49[9]
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
Mass0.90 ± 0.04[10] M☉
Radius0.91 ± 0.03[11] R☉
Luminosity (bolometric)0.59 ± 0.02[11] L☉
Surface gravity (log g)4.5[12] cgs
Temperature5,300[12] K
Metallicity [Fe/H]+0.04[13] dex
Rotation19.7 days[13]
Age1.9[14] Gyr
70 Oph B
Mass0.70 ± 0.07[10] M☉
Luminosity (bolometric)0.13 ± 0.03[10] L☉
Temperature4,350 ± 150[10] K
Other designations
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
SIMBADThe system
A
B
Exoplanet Archivedata
ARICNSdata

History

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. He commented at the time that there was a possible third unseen companion affecting the orbit of the two visible stars.[15]

Variability

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]

Binary star

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 (at e=0.499), the separation between the two varies from 11.4 to 34.8 AU, with one orbit taking 88.38 years to complete.[16]

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".[17] 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. [18]

T. J. J. See made a stronger claim for the existence of a dark companion in this system in 1899,[15] but Forest Ray Moulton soon published a paper proving that a three-body system with the specified orbital parameters would be highly unstable.[19] The claims by Jacob and See have both been shown to be erroneous.[20]

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.[21] 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.[22] This caused quite a sensation at the time but later observations have gradually discredited this claim.[20][23][24]

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.[25]

See also

References
  1. 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
  2. "V2391 Oph". International Variable Star Index. AAVSO. Retrieved 2018-10-07.
  3. Fabricius, C.; Høg, E.; Makarov, V. V.; Mason, B. D.; Wycoff, G. L.; Urban, S. E. (2002). "The Tycho double star catalogue". Astronomy and Astrophysics. 384: 180–189. Bibcode:2002A&A...384..180F. doi:10.1051/0004-6361:20011822.
  4. Brown, A. G. A.; et al. (Gaia collaboration) (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics. 616. A1. arXiv:1804.09365. Bibcode:2018A&A...616A...1G. doi:10.1051/0004-6361/201833051. Gaia DR2 record for this source at VizieR.
  5. Cowley, A. P.; Hiltner, W. A.; Witt, A. N. (1967). "Spectral classification and photometry of high proper motion stars". The Astronomical Journal. 72: 1334. Bibcode:1967AJ.....72.1334C. doi:10.1086/110413.
  6. Ducati, J. R. (2002). "VizieR Online Data Catalog: Catalogue of Stellar Photometry in Johnson's 11-color system". VizieR On-line Data Catalog. Bibcode:2002yCat.2237....0D.
  7. "GCVS Query= V2391 Oph". General Catalog of Variable Stars. Sternberg Astronomical Institute, Moscow, Russia. Retrieved 2018-03-08.
  8. Pourbaix, D. (2000). "Resolved double-lined spectroscopic binaries: A neglected source of hypothesis-free parallaxes and stellar masses". Astronomy and Astrophysics Supplement Series. 145 (2): 215–222. Bibcode:2000A&AS..145..215P. doi:10.1051/aas:2000237.
  9. 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:0811.3982, Bibcode:2009A&A...501..941H, doi:10.1051/0004-6361/200811191.
  10. 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
  11. 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
  12. 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
  13. 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
  14. 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
  15. 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.
  16. Solstation article giving details of orbital mechanics of the system
  17. Jacob, W.S. (1855). "On Certain Anomalies presented by the Binary Star 70 Ophiuchi". Monthly Notices of the Royal Astronomical Society. 15 (9): 228–230. Bibcode:1855MNRAS..15..228J. doi:10.1093/mnras/15.9.228.
  18. "The First Exoplanet Claim: Captain William S Jacob".
  19. 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.
  20. 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.
  21. Berman, Louis (1932). "70 Ophiuchi as a Triple System". Lick Observatory Bulletin (443): 24–30. Bibcode:1932LicOB..16...24B. doi:10.5479/ADS/bib/1932LicOB.16.24B.
  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. van de Kamp, Peter (February 1945). "Stars Nearer than Five Parsecs". Publications of the Astronomical Society of the Pacific. 57 (334): 34-41 (38*). Bibcode:1945PASP...57...34V. doi:10.1086/125679.
  24. Worth, M.D. (November 1974). "Parallax, orbit, and mass of the binary star 70 Ophiuchi". Astrophysical Journal. 193: 647–650. Bibcode:1974ApJ...193..647W. doi:10.1086/153202.
  25. 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.

This article is issued from Wikipedia. The text is licensed under Creative Commons - Attribution - Sharealike. Additional terms may apply for the media files.