Zeta Sagittarii
 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] |
| Characteristics | |
| Spectral type | A2.5 Va[4] |
| U−B color index | +0.05[2] |
| B−V color index | +0.08[2] |
| Astrometry | |
| 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] |
| Orbit[3] | |
| Period (P) | 21.00 ± 0.01 years |
| Semimajor 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) (secondary) |
7.2 ± 0.6° |
| Details | |
| Surface gravity (log g) | 3.90[6] |
| Temperature | 8,799[6] K |
| Rotational velocity (v sin i) | 77[7] km/s |
| Other designations | |
Zeta Sagittarii (ζ Sgr, ζ Sagittarii) 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 from a Late Latin word meaning armpit. In ancient Chinese astronomy, it is the 6th star of 6 stars in the Dipper or 'South Dipper' mansion of the Black Tortoise of the North. 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 (2.3 ± 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.
[edit] See also
- USS Ascella (AK-137) was a United States Navy Crater class cargo ship named after the star.
[edit] References
- ^ a b c d e f van Leeuwen, F. (November 2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics 474 (2): 653–664, Bibcode 2007A&A...474..653V, doi:10.1051/0004-6361:20078357
- ^ 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.
- ^ 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
- ^ a b c "CCDM J19026-2953AB -- Double or multiple star", SIMBAD Astronomical Object Database (Centre de Données astronomiques de Strasbourg), http://simbad.u-strasbg.fr/simbad/sim-id?Ident=Zeta+Sagittarii, retrieved 2012-02-18
- ^ a b Wilson, R. E. (1953). General Catalogue of Stellar Radial Velocities. Carnegie Institute of Washington D.C.. Bibcode 1953GCRV..C......0W.
- ^ 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, Bibcode 2003AJ....126.2048G, doi:10.1086/378365
- ^ 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, Bibcode 2007A&A...463..671R, doi:10.1051/0004-6361:20065224
- ^ 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
- ^ Kaler, James B., "ASCELLA (Zeta Sagittarii)", Stars (University of Illinois), http://stars.astro.illinois.edu/sow/ascella.html, retrieved 2012-02-18
