Eta Scorpii

Eta Scorpii

Eta Scorpii
Diagram showing star positions and boundaries of the Scorpius constellation and its surroundings

Location of η Scorpii (circled)
Observation data
Epoch J2000      Equinox J2000
Constellation Scorpius
Right ascension 17h 12m 09.19565s[1]
Declination –43° 14′ 21.0905″[1]
Apparent magnitude (V) 3.33[2]
Spectral type F5 IV[3]
U−B color index +0.09[2]
B−V color index +0.41[2]
Radial velocity (Rv) –27.0[4] km/s
Proper motion (μ) RA: +24.47[1] mas/yr
Dec.: –288.55[1] mas/yr
Parallax (π) 44.39 ± 0.16[1] mas
Distance 73.5 ± 0.3 ly
(22.53 ± 0.08 pc)
Absolute magnitude (MV) +1.58[5]
Mass 1.75[6] M
Luminosity 17.7[6] L
Surface gravity (log g) 3.10[3] cgs
Temperature 6,519[3] K
Metallicity [Fe/H] 0.05[5] dex
Rotational velocity (v sin i) 150.0[6] km/s
Age 1.1[5] Gyr
Other designations
Eta Sco, CD-43 11485, FK5 638, GJ 657, HD 155203, HIP 84143, HR 6380, SAO 227707.[7]

Eta Scorpii (η Sco, η Scorpii) is a star in the southern zodiac constellation of Scorpius. With an apparent visual magnitude of 3.33,[2] this is one of the brighter members of the Scorpius and is the furthest south of the constellation stars with a Bayer designation.[8] The distance to this star can be estimated using parallax measurements, yielding a value of 73.5 light-years (22.5 parsecs) with a 0.4% margin of error.[1]

The stellar classification of this star has undergone some revision over time, with the star being classified anywhere from an F-type main sequence star to a giant star.[7] In 2006, the NStars program assigned it a class of F5 IV,[3] where the luminosity class of 'IV' indicates this is a subgiant star that is exhausting the supply of hydrogen at its core and is in the process of evolving into a giant star. It has around 175%[6] of the Sun's mass with an estimated age of 1.1 billion years.[5] The star is radiating about 18[6] times the luminosity of the Sun from its outer atmosphere at an effective temperature of 6,519 K.[3] It is this heat that gives it a yellow-white hue that is typical for an F-type star.[9]

Eta Scorpii is rotating rapidly, with a projected rotational velocity of 150 km s−1.[6] This is causing the star to spin on its axis with a period of less than a day.[10] It is an X-ray emitter with its stellar corona giving off an X-ray luminosity of 4.4 × 1028 ergs s−1.[11] In 1991 it was identified as a possible barium star, as it displays an enhanced abundance of the element barium in its spectrum.[12] Overall, the abundance of elements other than hydrogen and helium, what astronomers term the star's metallicity, is similar to the abundance in the Sun.[5]


  1. ^ a b c d e f van Leeuwen, F. (November 2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics 474 (2): 653–664,  
  2. ^ a b c d Bok, B. J.; Bok, P. F.; Miller, E. W. (November 1972), "Photometric standards for the southern hemisphere. II", Astronomical Journal 77: 733,  
  3. ^ a b c d e Gray, R. O.; et al. (July 2006), "Contributions to the Nearby Stars (NStars) Project: Spectroscopy of Stars Earlier than M0 within 40 pc-The Southern Sample", The Astronomical Journal 132 (1): 161–170,  
  4. ^ Evans, D. S. (June 20–24, 1966), Batten, Alan Henry; Heard, John Frederick, eds., The Revision of the General Catalogue of Radial Velocities, University of Toronto: International Astronomical Union, retrieved 2009-09-10 
  5. ^ a b c d e Holmberg, J.; Nordstrom, B.; Andersen, J. (July 2009). "The Geneva-Copenhagen survey of the solar neighbourhood. III. Improved distances, ages, and kinematics". Astronomy and Astrophysics 501 (3): 941–947.  
  6. ^ a b c d e f Mallik, Sushma V.; Parthasarathy, M.; Pati, A. K. (October 2003), "Lithium and rotation in F and G dwarfs and subgiants", Astronomy and Astrophysics 409: 251–261,  
  7. ^ a b "LTT 6848 -- High proper-motion Star", SIMBAD (Centre de Données astronomiques de Strasbourg), retrieved 2012-02-10 
  8. ^ Burnham, Robert (1978), Burnham's celestial handbook: an observer's guide to the universe beyond the solar system, Dover books explaining science 3 (2nd ed.), Courier Dover Publications, p. 1675,  
  9. ^ "The Colour of Stars", Australia Telescope, Outreach and Education (Commonwealth Scientific and Industrial Research Organisation), December 21, 2004, retrieved 2012-02-10 
  10. ^ Kaler, James B., "Eta Scorpii", Stars (University of Illinois), retrieved 2012-02-10 
  11. ^ Pizzolato, N.; Maggio, A.; Sciortino, S. (September 2000), "Evolution of X-ray activity of 1-3 Msun late-type stars in early post-main-sequence phases", Astronomy and Astrophysics 361: 614–628,  
  12. ^ Lu, Phillip K. (June 1991), "Taxonomy of barium stars", Astronomical Journal 101: 2229–2254,