Zeta Sagittarii

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Zeta Sagittarii
Diagram showing star positions and boundaries of the Sagittarius constellation and its surroundings
Cercle rouge 100%.svg

Location of ζ Sagittarii (circled) near the center
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Sagittarius
Right ascension 19h 02m 36.73024s[1]
Declination –29° 52′ 48.2279″[1]
Apparent magnitude (V) +2.59[2] (3.27/3.48)[3]
Spectral type A2.5 Va[4]
U−B color index +0.05[2]
B−V color index +0.08[2]
Radial velocity (Rv) +22[5] km/s
Proper motion (μ) RA: +10.79[1] mas/yr
Dec.: +21.11[1] mas/yr
Parallax (π) 36.98 ± 0.87[1] mas
Distance 88 ± 2 ly
(27.0 ± 0.6 pc)
Absolute magnitude (MV) 1.11/1.32[3]
Period (P) 21.00 ± 0.01 years
Semi-major axis (a) 0.489 ± 0.001"
Eccentricity (e) 0.211 ± 0.001
Inclination (i) 111.1 ± 0.1°
Longitude of the node (Ω) 74.0 ± 0.1°
Periastron epoch (T) 2005.99 ± 0.03
Argument of periastron (ω)
7.2 ± 0.6°
Surface gravity (log g) 3.90[6] cgs
Temperature 8,799[6] K
Rotational velocity (v sin i) 77[7] km/s
Other designations
Ascella, ζ Sagittarii, ζ Sgr, Zeta Sgr, 38 Sagittarii, CCDM J19026-2953AB, CPD-30  5798, GC 26161, HD 176687, HIP 93506, HR 7194, IDS 18562-3001 AB, PPM 269230, SAO 187600, WDS J19026-2953AB.[4]

Zeta Sagittarii (Zeta Sgr, ζ Sagittarii, ζ Sgr) is the third brightest star system in the constellation Sagittarius, with an apparent visual magnitude of +2.59.[2] It has the traditional name Ascella. Based upon parallax measurements, the distance to Ascella is about 88 ly (27 pc).[1] Ascella is moving away from the Solar System with a radial velocity of 22 km s−1.[5] Some 1.0–1.4 million years ago, this system came within 7.5 ± 1.8 ly (2.30 ± 0.55 pc) of the Sun.[8]

This is a binary star system, with the two components orbiting each other over a period of 21 years at an eccentricity of 0.211. The combined mass of the system is 5.26 ± 0.37 times the mass of the Sun[3] and their blended stellar classification is A2.5 Va.[4]

The system consists of a spectral class A2 giant with an apparent magnitude of +3.27, and an A4 subgiant with apparent magnitude of +3.48. The pair have a mean separation of 13.4 astronomical units (AU).[9] Ascella has a faint, 10th magnitude companion, separated from the primary by a distance of 75 arcseconds.

Name and etymology[edit]



  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, arXiv:0708.1752, Bibcode:2007A&A...474..653V, doi:10.1051/0004-6361:20078357 
  2. ^ a b c d Johnson, H. L.; et al. (1966). "UBVRIJKL photometry of the bright stars". Communications of the Lunar and Planetary Laboratory 4 (99). Bibcode:1966CoLPL...4...99J. 
  3. ^ a b c d De Rosa, Robert J.; et al. (2011), "The VAST Survey -- II. Orbital motion monitoring of A-type star multiples", Monthly Notices of the Royal Astronomical Society 422: 2765–2785, arXiv:1112.3666, Bibcode:2012MNRAS.422.2765D, doi:10.1111/j.1365-2966.2011.20397.x 
  4. ^ a b c "CCDM J19026-2953AB -- Double or multiple star", SIMBAD Astronomical Object Database (Centre de Données astronomiques de Strasbourg), retrieved 2012-02-18 
  5. ^ a b Wilson, R. E. (1953). General Catalogue of Stellar Radial Velocities. Carnegie Institute of Washington D.C. Bibcode:1953GCRV..C......0W. 
  6. ^ a b Gray, R. O.; et al. (October 2003), "Contributions to the Nearby Stars (NStars) Project: Spectroscopy of Stars Earlier than M0 within 40 Parsecs: The Northern Sample. I.", The Astronomical Journal 126 (4): 2048–2059, arXiv:astro-ph/0308182, Bibcode:2003AJ....126.2048G, doi:10.1086/378365 
  7. ^ Royer, F.; Zorec, J.; Gómez, A. E. (February 2007), "Rotational velocities of A-type stars. III. Velocity distributions", Astronomy and Astrophysics 463 (2): 671–682, arXiv:astro-ph/0610785, Bibcode:2007A&A...463..671R, doi:10.1051/0004-6361:20065224 
  8. ^ Dybczyński, P. A. (April 2006), "Simulating observable comets. III. Real stellar perturbers of the Oort cloud and their output", Astronomy and Astrophysics 449 (3): 1233–1242, Bibcode:2006A&A...449.1233D, doi:10.1051/0004-6361:20054284 
  9. ^ Kaler, James B., "ASCELLA (Zeta Sagittarii)", Stars (University of Illinois), retrieved 2012-02-18 
  10. ^ "Sagittarius". deepsky.astroinfo.org. Retrieved 30 August 2008. 
  11. ^ skywatchers Archived June 29, 2004, at the Wayback Machine.
  12. ^ a b c Allen, R. H. (1963). Star Names: Their Lore and Meaning (Reprint ed.). New York: Dover Publications Inc. p. 355. ISBN 0-486-21079-0. Retrieved 2012-09-04. 
  13. ^ Knobel, E. B. (June 1895). "Al Achsasi Al Mouakket, on a catalogue of stars in the Calendarium of Mohammad Al Achsasi Al Mouakket". Monthly Notices of the Royal Astronomical Society 55: 430. Bibcode:1895MNRAS..55..429K. doi:10.1093/mnras/55.8.429. 
  14. ^ (Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 5 月 11 日