<templatestyles src="Template:Sky/styles.css" />Coordinates: Sky map 17h 34m 56.06945s, +12° 33′ 36.1346″

Alpha Ophiuchi

From Wikipedia, the free encyclopedia
Jump to navigation Jump to search

Template:Short description

α Ophiuchi
Template:Location mark
Location of α Ophiuchi (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Ophiuchus
Right ascension Template:RA[1]
Declination Template:DEC[1]
Apparent magnitude (V) 2.07[2]
Characteristics
Spectral type A5IVnn[3] / K5–7 V[4]
U−B Template:Engvar +0.10[2]
B−V Template:Engvar +0.15[2]
Astrometry
Radial velocity (Rv)+12.6[5] km/s
Proper motion (μ) RA: +108.07[1] mas/yr
Dec.: −221.57[1] mas/yr
Parallax (π)67.13±1.06 mas[1]
DistanceTemplate:Rnd ± Template:Rnd ly
(Template:Rnd ± Template:Rnd pc)
Absolute magnitude (MV)+1.248[6]
Orbit[7]
Period (P)Script error: No such module "val". days
Semi-major axis (a)Script error: No such module "val".
Eccentricity (e)Script error: No such module "val".
Inclination (i)Script error: No such module "val".°
Longitude of the node (Ω)Script error: No such module "val".°
Periastron epoch (T)Script error: No such module "val".
Argument of periastron (ω)
(secondary)		Script error: No such module "val".°
Semi-amplitude (K1)
(primary)		Script error: No such module "val". km/s
Semi-amplitude (K2)
(secondary)		Script error: No such module "val". km/s
Details
α Oph A
MassScript error: No such module "val".[7] Template:Solar mass
RadiusScript error: No such module "val". (equatorial)
Script error: No such module "val". (polar)[8] Template:Solar radius
LuminosityScript error: No such module "val".[8] Template:Solar luminosity
Surface gravity (log g)3.91[9] cgs
TemperatureScript error: No such module "val". (equatorial)
Script error: No such module "val". (polar)[8] K
Rotation0.61[8] days
Rotational velocity (v sin i)Script error: No such module "val".[8] km/s
AgeScript error: No such module "val".[10] Gyr
α Oph B
MassScript error: No such module "val".[7] Template:Solar mass
Metallicity [Fe/H]{{{metal_fe2}}} dex
Other designations
Template:Odlist[11]
Database references
SIMBADdata

Script error: No such module "Check for unknown parameters".

Alpha Ophiuchi (α Ophiuchi, abbreviated Alpha Oph, α Oph), also named Rasalhague Template:IPAc-en,[12][13] is a binary star and the brightest star in the constellation of Ophiuchus.

Nomenclature

The name Alpha Ophiuchi is a Romanisation of the star's Bayer designation, α Ophiuchi. It is also known by the traditional name Rasalhague, from the Arabic رأس الحواء raʼs al-ḥawwāʼ "the head of the serpent collector".[13] In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)[14] to catalog and standardize proper names for stars. The WGSN's first bulletin of July 2016[15] included a table of the first two collections of approved names, formally listing Alpha Ophiuchi as Rasalhague.[16]

In Chinese astronomy, this star is named Hòu (Template:Lang-zh), representing a senior assistant to the emperor, sometimes said to be an astrologer.[17][18]

Properties

Alpha Ophiuchi is a binary star system with an orbital period of about 8.62 years. The orbital parameters were only poorly known until 2011 when observations using adaptive optics produced a better orbital fit, allowing the individual masses of the two components to be determined.[4] The orbital elements and masses were further improved in a 2021 study.[7] The primary component, Alpha Ophiuchi A, has a mass of about 2.2 times the mass of the Sun, while the secondary, Alpha Ophiuchi B, has 0.82 solar masses.[7] Estimates of the mass of the primary by other means range from a low of 1.92 to 2.10 solar masses, up to 2.84 or even 4.8 solar masses.[10] The mass of the secondary suggests that it has a stellar classification in the range K5V to K7V, which indicates it is a main sequence star that is still generating energy by the thermonuclear fusion of hydrogen at its core. The pair reached periastron passage, or closest approach, around April 19, 2012, when they had an angular separation of 50 milliarcseconds.[4]

This star system has a combined apparent magnitude of +2.07 and is located at a distance of about Script error: No such module "convert". from the Earth. The stellar classification of A5IVnn indicates that the primary is a bluish-white subgiant star that has evolved away from the main sequence after consuming the hydrogen at its core.[3] It is radiating about 25 times the luminosity of the Sun and has an effective temperature of about 8,000 K, giving it the characteristic white hue of an A-type star.[19][20]

The spectrum of Alpha Ophiuchi shows an anomalously high level of absorption of the lines for singly-ionized calcium (Ca II). However, this is likely the result of interstellar matter between the Earth and the star, rather than a property of the star or circumstellar dust.[21]

Rotation

File:Eso0316c.tif
A rapidly-rotating star is distorted into an oblate spheroid bulging at the equator and hotter at the poles.

Alpha Ophiuchi A is a rapidly rotating star with a projected rotational velocity of 240 km s−1.[19] It is spinning at about 88.5% of the rate that would cause the star to break up.[22] This gives it an oblate spheroid shape with an equatorial bulge about 20% larger than the polar radius.[10] The polar radius is calculated to be Template:Solar radius and the equatorial radius Template:Solar radius.[8]

Because of the oblateness and rapid spin, the surface gravity at the pole is higher than at the equator. An effect known as gravity darkening means that the temperature at the poles is also higher than at the equator. The polar temperature is calculated to be Script error: No such module "val". and the equatorial temperature Script error: No such module "val"..[8]

The energy radiated by an oblate star is higher along its axis of rotation because of the larger projected area and the Stefan–Boltzmann law. The axis of rotation of α Ophiuchi is inclined about 87.7° ± 0.4° to the line of sight from the Earth, so that it is being observed from nearly equator-on.[22] The apparent bolometric luminosity seen at this angle is Template:Solar luminosity, but the true luminosity of the star is thought to be Template:Solar luminosity. Since a star's effective temperature is simply the temperature which would produce its total energy output from a black body, the true effective temperature of Script error: No such module "val". is different from the apparent effective temperature of Script error: No such module "val"..[8]

See also

References

<templatestyles src="Reflist/styles.css" />

  1. ↑ a b c d e Script error: No such module "citation/CS1".
  2. ↑ a b c Script error: No such module "citation/CS1".
  3. ↑ a b Script error: No such module "citation/CS1".
  4. ↑ a b c Script error: No such module "citation/CS1".
  5. ↑ Script error: No such module "citation/CS1".
  6. ↑ Script error: No such module "Citation/CS1".
  7. ↑ a b c d e Script error: No such module "Citation/CS1".
  8. ↑ a b c d e f g h Script error: No such module "Citation/CS1".
  9. ↑ Script error: No such module "citation/CS1".
  10. ↑ a b c Script error: No such module "citation/CS1".
  11. ↑ Script error: No such module "citation/CS1".
  12. ↑ also Template:IPAc-en or Template:IPAc-en.
    Template:MW
  13. ↑ a b Script error: No such module "citation/CS1".
  14. ↑ Script error: No such module "citation/CS1".
  15. ↑ Script error: No such module "citation/CS1".
  16. ↑ Script error: No such module "citation/CS1".
  17. ↑ Script error: No such module "citation/CS1".
  18. ↑ Script error: No such module "citation/CS1".
  19. ↑ a b Script error: No such module "citation/CS1".
  20. ↑ Script error: No such module "citation/CS1".
  21. ↑ Script error: No such module "citation/CS1".
  22. ↑ a b Script error: No such module "citation/CS1".

Script error: No such module "Check for unknown parameters".

External links

  • Script error: No such module "citation/CS1".


Template:Stars of Ophiuchus

Retrieved from "http://debianws.lexgopc.com/wiki143/index.php?title=Alpha_Ophiuchi&oldid=6172370"