Epsilon Ophiuchi

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Star
ε Ophiuchi
Diagram showing star positions and boundaries of the Ophiuchus constellation and its surroundings
Cercle rouge 100% .svg
AladinLite
Observation
dates equinox :  J2000.0 , epoch : J2000.0
Constellation Snake bearer
Right ascension 16 h 18 m 19.3 s
declination -04 ° 41 ′ 33 ″
Apparent brightness 3.2 mag
Typing
B − V color index +0.762 
U − B color index +0.972 
Spectral class G 9.5 IIIb
Astrometry
Radial velocity −10.3 km / s
parallax 30.64 ± 0.20  mas
distance 106.4 ± 0.7  ly
32.6 ± 0.2  pc
Visual absolute brightness M vis 0.55 mag
Proper movement 
Rec. Share: approx. +83  mas / a
Dec. portion: approx. +41  mas / a
Physical Properties
Dimensions 1.85  M ☉
radius 10.4  R ☉
Luminosity

54  L ☉

Effective temperature 4900  K
Metallicity [Fe / H] −0.13
Rotation time 5.7
Age 1.0 billion  a
Other names
and catalog entries
Bayer name ε Ophiuchi
Flamsteed name 2 Ophiuchi
Bonn survey BD −4 ° 4086
Bright Star Catalog HR 6075 [1]
Henry Draper Catalog HD 146791 [2]
Gliese catalog FY 3949 [3]
Hipparcos catalog HIP 79882 [4]
SAO catalog SAO 141086 [5]
Tycho catalog TYC 5042-999-1 [6]
Other names FK5  605

Epsilon Ophiuchi ( ε Ophiuchi , abbreviated Epsilon Oph , ε Oph ) is a star in the constellation of the Serpent Bearer . It belongs to the spectral class G with an apparent visual brightness of 3.2 mag. This corresponds to a third magnitude star. According to measurements of the parallax by Hipparcos , the star is about 106 light years away from Earth. He bears the proper name Yed Posterior (Arabic يد jad / Latin), "following hand". It forms a visual double star , visible to the naked eye, with Delta Ophiuchi (proper name: Yed Prior , distance approx. 170 light years).

nomenclature

ε Ophiuchi is the Bayer name for the star.

The traditional name of this star is Yed Posterior . Yed is derived from the Arabic word "Yad" and means "the hand". Epsilon and Delta Ophiuchi together form the left hand of Ophiuchus (serpent bearer), which holds the head of a blow. This head is called "Serpens Caput" and is a constellation of stars in the constellation Snake . Since October 5, 2016, the name "Yed Posterior" has been the standard name of this star, included in the list of star names of the International Astronomical Union .

properties

Epsilon Ophiuchi belongs to the spectral class G 9 IIIb. The star is a yellow giant star . It has almost used up its hydrogen supply for nuclear fusion. As a result, its outer sheaths have expanded significantly. It has about twice the solar mass. Its radius is an estimated ten solar radii. This makes it about 54 times more luminous than the sun. Its age is approximately 1 billion years.

Analyzes of the star spectrum indicate a lack of CN (cyan) and C (carbon).

The outer shells of the star show a Sun-like oscillation with a period of 0.19 days. This allows the use of astroseismological methods .

So far, the method of energy generation from the star has not been exactly clarified. There is either the possibility of nuclear fusion of hydrogen within star shells ( shell burning ), or the fusion of helium within the core. Both methods can explain the physical properties of the star.

The star's equatorial rotation speed is 5.7 km / s. The axis of rotation is at an angle of 41–73 ° to the star's line of sight from Earth.

Web links

  • Jim Kaler: Yed Posterior . In: STARS . Archived from the original on June 25, 2005. Retrieved on July 1, 2018.

Individual evidence

  1. ↑ a b Naming Stars . IAU.org. Retrieved June 28, 2018.
  2. ^ R. Earle Luck: Chemical abundances for cyanogen-weak giants . In: Astrophysical Journal Supplement Series . 75, 1991, p. 579. bibcode : 1991ApJS ... 75..579L . doi : 10.1086 / 191542 .