  | |
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Ophiuchus |
| Right ascension | 16h 37m 09.54001s[1] |
| Declination | −10° 34′ 01.5097″[1] |
| Apparent magnitude (V) | 2.56 – 2.58[2] |
| Characteristics | |
| Spectral type | O9.5 V[3] |
| U−Bcolor index | −0.857[4] |
| B−Vcolor index | +0.032[4] |
| Variable type | γ Cas[2] +β Cep[3] |
| Astrometry | |
| Radial velocity (Rv) | −15.0[5] km/s |
| Proper motion (μ) | RA: +10.465mas/yr[1] Dec.: +24.742mas/yr[1] |
| Parallax (π) | 7.4088±0.6596 mas[1] |
| Distance | 440 ± 40 ly (130 ± 10 pc)[1] |
| Absolute magnitude (MV) | −4.2[6] |
| Details | |
| Mass | 20.2[7] M☉ |
| Radius | 9.1 (equator) 7.5 (polar)[6] R☉ |
| Luminosity | 74,100[7] L☉ |
| Surface gravity (log g) | 3.58[6] cgs |
| Temperature | 30,700 (equatorial) 39,000 (polar)[6] K |
| Rotational velocity (v sin i) | 400[3] km/s |
| Age | 3.0±0.3[8] Myr |
| Other designations | |
| 13 Oph,BD−10°4350, FK5 622,HD 149757,HIP 81377,HR 6175,SAO 160006,2MASS J16370954-1034014, Gaia DR2 4337352305315545088 | |
| Database references | |
| SIMBAD | data |
Zeta Ophiuchi (ζ Oph, ζ Ophiuchi) is a single[9]star located in theconstellation ofOphiuchus. It has anapparent visual magnitude of 2.6, making it the third-brightest star in the constellation.Parallax measurements give an estimated distance of roughly 440light-years (130parsecs) from theEarth.[1] It is surrounded by the Sh2-27 "Cobold" nebula, the star's bow shock as it ploughs through dense dust clouds near theRho Ophiuchi cloud complex.
In April 2010, ζ Ophiuchi wasocculted by asteroid824 Anastasia.[10][11][12]
ζ Ophiuchi is an enormous star with more than 20[8] times theSun's mass and eight[13] times itsradius. Thestellar classification of this star isO9.5 V,[3] with theluminosity class of V indicating that it is generating energy in its core by thenuclear fusion of hydrogen. From Earth, the apparenteffective temperature of the star appears to be 34,300K,[13] giving the star the blue hue of anO-type star.[14] However, since the star is rapidly rotating, the exact surface temperature varies across the surface of the star from as high as 39,000K at the poles to as low as 30,700K at the equator.[13] Theprojected rotational velocity may be as high as400[3] km s−1 and it may be rotating at a rate of once per day, close to the velocity at which it would begin to break up.
This is a young star with an age of only three million years.[8] Its luminosity is varying in a periodic manner similar to that of aBeta Cephei variable. This periodicity has a dozen or more frequencies ranging between 1–10 cycles per day.[3] In 1979, examination of the spectrum of this star found "moving bumps" in its helium line profiles. This feature has since been found in other stars, which have come to be called ζ Oph stars. These spectral properties are likely the result of non-radial pulsations.[16]
This star is roughly halfway through the initial phase of itsstellar evolution and will, within the next few million years, expand into a redsupergiant star wider than the orbit ofJupiter before ending its life in asupernova explosion, leaving behind aneutron star orpulsar. From the Earth, a significant fraction of the light from this star is absorbed by interstellar dust, particularly at the blue end of the spectrum. In fact, were it not for this dust, ζ Ophiuchi would shine several times brighter and be among the very brightest stars visible.[17] If the star's luminosity were not obscured, it would shine at magnitude 1.54, becoming thetwenty-third brightest star in the night sky.[note 1]
X-ray emissions have been detected from Zeta Ophiuchi that vary periodically. The net X-ray flux is estimated at1.2×1024 W. In the energy range of 0.5–10 keV, this flux varies by about 20% over a period of 0.77 days. This behavior may be the result of a magnetic field in the star. The measured average strength of the longitudinal field is about14.1±4.5 mT.[3]
ζ Ophiuchi is moving through space with apeculiar velocity of 30 km s−1. Based upon the age and direction of motion of this star, it is a member of the Upper Scorpius sub-group of theScorpius–Centaurus association of stars that share a common origin andspace velocity.[18] Suchrunaway stars may be ejected by dynamic interactions between three or four stars. However, in this case the star may be a former component of abinary star system in which the more massive primary was destroyed in atype II supernova explosion.[3] It is possible that ζ Ophiuchiaccreted mass from its companion before it was ejected.[19] The pulsarPSR B1929+10 may be the leftover remnant of this supernova, as it too was ejected from the association with a velocity vector that fits the scenario.[3]
Due to the highspace velocity of Zeta Ophiuchi, in combination with high intrinsic brightness and its current location in a dust-rich area of the galaxy, the star is creating abow-shock in the direction of motion. This shock has been made visible via NASA'sWide-field Infrared Survey Explorer.[20] The formation of this bow shock can be explained by a mass loss rate of about1.1×10−7 times themass of the Sun per year, which equals the mass of the Sun every nine million years.[3]
ζ Ophiuchi was a member of indigenous Arabicasterism al-Nasaq al-Yamānī, "the Southern Line" ofal-Nasaqān "the Two Lines",[21] along withα Serpentis (Unukalhai),δ Ser (Qin, Tsin),ε Ser (Ba, Pa),δ Ophiuchi (Yed Prior),ε Oph (Yed Posterior) andγ Oph (Tsung Ching).[22]
According to the catalogue of stars in theTechnical Memorandum 33-507 – A Reduced Star Catalog Containing 537 Named Stars,al-Nasaq al-Yamānī or Nasak Yamani was the title for two stars:δ Serpentis asNasak Yamani I andε Ser asNasak Yamani II (exclude this star,α Ser,δ Ophiuchi,ε Oph andγ Oph)[23]
InChinese,天市右垣 (Tiān Shì Yòu Yuán), meaningRight Wall of Heavenly Market Enclosure, refers to an asterism which is represent eleven old states in China which is marking the right borderline of the enclosure, consisting of ζ Ophiuchi,β Herculis,γ Herculis,κ Herculis,γ Serpentis,β Serpentis,α Serpentis,δ Serpentis,ε Serpentis,δ Ophiuchi andε Ophiuchi.[24] Consequently, theChinese name for ζ Ophiuchi itself is天市右垣十一 (Tiān Shì Yòu Yuán shíyī, English:the Eleventh Star of Right Wall of Heavenly Market Enclosure), represent the stateHan (韓),[25][26][27] together with35 Capricorni[28] inTwelve States (asterism).
