36 Ophiuchi

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36 Ophiuchi A/B/C

A visual band light curve for 36 Ophiuchi C (V2215 Ophiuchi), plotted from ASAS-SN data[1]
Observation data Epoch J2000      Equinox J2000
Constellation	Ophiuchus
Right ascension	A: 17h 15m 20.851s B: 17h 15m 20.978s C: 17h 16m 13.3624s[2]
Declination	A: −26° 36′ 09.04″ B: −26° 36′ 10.18″ C: −26° 32′ 46.129″[2]
Apparent magnitude (V)	5.08/5.03/6.34[2]
Characteristics
Spectral type	K2 V/K1 V/K5 V[2]
U−B color index	0.51(AB)/1.04
B−V color index	0.85(AB)/1.16
Variable type	C: RS CVn
Astrometry
36 Oph A
Radial velocity (Rv)	−0.6[2] km/s
Proper motion (μ)	RA: −498.600±0.123[3] mas/yr Dec.: −1149.158±0.086[3] mas/yr
Parallax (π)	168.0031 ± 0.1343 mas[3]
Distance	19.41 ± 0.02 ly (5.952 ± 0.005 pc)
36 Oph B
Radial velocity (Rv)	0.0[2] km/s
Proper motion (μ)	RA: −465.861±0.111[4] mas/yr Dec.: −1141.168±0.073[4] mas/yr
Parallax (π)	168.1303 ± 0.1081 mas[4]
Distance	19.40 ± 0.01 ly (5.948 ± 0.004 pc)
36 Oph C
Radial velocity (Rv)	−0.04±0.22[5] km/s
Proper motion (μ)	RA: −479.573±0.031[5] mas/yr Dec.: −1124.332±0.020[5] mas/yr
Parallax (π)	167.9617 ± 0.0311 mas[5]
Distance	19.418 ± 0.004 ly (5.954 ± 0.001 pc)
Orbit
Companion	36 Ophiuchi B
Period (P)	568.9 yr
Semi-major axis (a)	14.7″
Eccentricity (e)	0.922
Inclination (i)	99.6°
Longitude of the node (Ω)	−83.6°
Periastron epoch (T)	1,763.39
Details
36 Oph A
Radius	0.817 ± 0.016[6] R☉
Temperature	4,843 ± 134[6] K
Metallicity [Fe/H]	–0.20[6] dex
Age	0.6-1.8[7][8] Gyr
B
Temperature	4,985 ± 20[9] K
Metallicity [Fe/H]	–0.31 ± 0.042[9] dex
Other designations
36 Oph, WDS J17153-2636
AB: GJ 663, CD−26°12026, GCTP 3908.00, HIP 84405
A: Guniibuu, HR 6402, HD 155886, LHS 437, SAO 185198
B: HR 6401, HD 155885, LHS 438, SAO 185199
C: V2215 Ophiuchi, GJ 664, CD−26°12036, HD 156026, GCTP 3913.00, LHS 439, SAO 185213, HIP 84478
Database references
SIMBAD	AB
	A
	B
	C
Exoplanet Archive	A
	B
	C
ARICNS	A
	B
	C
36 Location of 36 Ophiuchi in the constellation Ophiuchus

36 Ophiuchi (or Guniibuu for component A) is a triple star system 19.5 light-years from Earth. It is in the constellation Ophiuchus.

The primary and secondary stars (also known as HD 155886) are nearly identical orange main-sequence dwarfs of spectral type K2/K1. This binary is unusual because its eruptions do not seem to conform to the Waldmeier effect; that is, the strongest eruptions of HD 155886 are not the ones characterized by the fast eruption onset.^[10] The tertiary star is an orange main-sequence dwarf of spectral type K5.

Star C is separated from the A-B pair by 700 arcseconds, compared to a minimum of 4.6 arcseconds for A-B, so its effect on the movements of the A-B pair is small. A and B have active chromospheres. At present the distance between the stars forming the AB-pair is 5.1 arcseconds and the position angle is 139 degrees, while star C is 731.6 arcseconds away from the A-component and situated at a position angle of 74 degrees.

In the beliefs of the Kamilaroi and Euahlayi Aboriginal peoples in New South Wales, Australia, the star is called Guniibuu that represents the robin red-breast bird (Petroica boodang). In 2016, the IAU organized a Working Group on Star Names (WGSN)^[11] to catalog and standardize proper names for stars. The WGSN approved the name Guniibuu for the star A on 10 August 2018 and it is now so included in the List of IAU-approved Star Names.^[12]

The McDonald Observatory team has set limits to the presence of one or more planets^[7] around 36 Ophiuchi A with masses between 0.13 and 5.4 Jupiter masses and average separations spanning between 0.05 and 5.2 astronomical units (AU), although beyond 1.5 AU orbits are inherently unstable around either 36 Ophiuchi A or 36 Ophiuchi B.^[13]

The star C (or namely HD 156026) is among five nearby paradigms as K-type stars of a type in a 'sweet spot’ between Sun-analog stars and M stars for the likelihood of evolved life, per analysis of Giada Arney from NASA's Goddard Space Flight Center.^[14]

^[1]

• Irwin, Alan W.; Yang, Stephenson L. S. & Walker, Gordon A. H. (1996), "36 Ophiuchi AB: Incompatibility of the Orbit and Precise Radial Velocities", Publications of the Astronomical Society of the Pacific, 108: 580, Bibcode:1996PASP..108..580I, doi:10.1086/133768
• Cayrel de Strobel, G.; Lebreton, Y.; Perrin, M.-N. & Cayrel, R. (1989), "A thorough spectroscopic study of the very nearby triple system - 36 Ophiuchi", Astronomy and Astrophysics, 225 (2): 369–380, Bibcode:1989A&A...225..369C
• Wittenmeyer, R. A.; Endl, Michael; Cochran, William D.; Hatzes, Artie P.; Walker, G. A. H.; Yang, S. L. S. & Paulson, Diane B. (2006), "Detection Limits from the McDonald Observatory Planet Search Program", Astronomical Journal, 132 (1): 177–188, arXiv:astro-ph/0604171, Bibcode:2006AJ....132..177W, doi:10.1086/504942, S2CID 16755455
• Barnes, Sydney A. (2007), "Ages for Illustrative Field Stars Using Gyrochronology: Viability, Limitations, and Errors", The Astrophysical Journal, 669 (2): 1167–1189, arXiv:0704.3068, Bibcode:2007ApJ...669.1167B, doi:10.1086/519295, S2CID 14614725

• "36 Ophiuchi". SolStation. Retrieved 3 November 2005.
• https://arxiv.org/abs/astro-ph/0604171