36 Ophiuchi is the system'sFlamsteed designation. Component C (HD 156026) was also historically called30 Scorpii.[14]
In the culture of theKamilaroi andEuahlayi Aboriginal peoples inNew South Wales, Australia, the star is calledGuniibuu and represents the robin red-breast bird (Petroica boodang).[15] In 2016, theIAU organized aWorking Group on Star Names (WGSN)[16] to catalog and standardize proper names for stars. The WGSN approved the nameGuniibuu for 36 Ophiuchi A on 10 August 2018 and it is now so included in the List of IAU-approved Star Names.[15]
The primary and secondary stars (also known as HD 155886) are nearly identical orangemain-sequence dwarfs ofspectral type K2/K1. This binary is unusual because its eruptions do not seem to conform to theWaldmeier effect; that is, the strongest eruptions of HD 155886 are not the ones characterized by the fast eruption onset.[17]
The tertiary star is an orange main-sequence dwarf ofspectral type K5. The age for this star derived usinggyrochronology is about 600 million years, while the age derived for the AB pair is 1.43 billion years. This discrepancy suggest that the A/B stars interacted with each other and slowed down their rotation periods, providing a spuriously higher age.[10]
Star C is separated from the A-B pair by 700arcseconds, 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 activechromospheres.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.
TheMcDonald Observatory team has set limits to the presence of one or more planets[19] around 36 Ophiuchi A with masses between 0.13 and 5.4Jupiter masses and average separations spanning between 0.05 and 5.2astronomical units (AU), although beyond 1.5 AU orbits are inherently unstable around either 36 Ophiuchi A or 36 Ophiuchi B.[20]
The star C (or namely HD 156026) is among five nearby paradigms asK-type stars of a type in a 'sweet spot’ between Sun-analog stars andM stars for the likelihood of evolved life, per analysis of Giada Arney fromNASA'sGoddard Space Flight Center.[21] It presents a significant difference onproper motion measurements taken by theHipparcos andGaia spacecrafts, suggesting the presence of a giant planet.[13]
^Wittenmyer, 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.S2CID16755455.
^Bill Steigerwald (2019-03-07).""Goldilocks" Stars May Be "Just Right" for Finding Habitable Worlds".NASA. Retrieved2020-05-12.'I find that certain nearby K stars like 61 Cyg A/B, Epsilon Indi, Groombridge 1618, and HD 156026 may be particularly good targets for future biosignature searches,' said Arney.
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.
