18 Sagittarii
18 Sagittarii is a single[7] star in zodiac constellation of Sagittarius,[6] located around 550 light years away from the Sun based on parallax.[1] It is visible to the naked eye as a faint, orange-hued star with an apparent visual magnitude of 5.58.[2] This object is moving closer to the Earth with a heliocentric radial velocity of −19 km/s.[2]
| Observation data Epoch J2000.0 Equinox J2000.0 (ICRS) | |
|---|---|
| Constellation | Sagittarius |
| Right ascension | 18h 25m 01.42751s[1] |
| Declination | −30° 45′ 23.6292″[1] |
| Apparent magnitude (V) | 5.58[2] |
| Characteristics | |
| Evolutionary stage | giant star |
| Spectral type | K0 III[3] |
| B−V color index | 1.138[4] |
| Astrometry | |
| Radial velocity (Rv) | −18.7±2.9[2] km/s |
| Proper motion (μ) | RA: −135.019[1] mas/yr Dec.: −70.932[1] mas/yr |
| Parallax (π) | 5.9260 ± 0.2434[1] mas |
| Distance | 550 ± 20 ly (169 ± 7 pc) |
| Absolute magnitude (MV) | −0.93[4] |
| Details | |
| Radius | 8.9[5] R☉ |
| Luminosity | 309.45[2] L☉ |
| Surface gravity (log g) | 1.50[4] cgs |
| Temperature | 4,341[4] K |
| Metallicity [Fe/H] | −0.79[4] dex |
| Rotational velocity (v sin i) | 1.0[4] km/s |
| Other designations | |
| Database references | |
| SIMBAD | data |
This is an aging giant star with a stellar classification of K0 III,[3] which indicates it has exhausted the hydrogen at its core and evolved away from the main sequence. It has expanded to about 9[5] times the Sun's radius and is radiating 309[2] times the Sun's luminosity from its enlarged photosphere at an effective temperature of 4,341.[4] There is a much lower abundance of iron in the spectrum compared to the Sun.[4]
References
- Brown, A. G. A.; et al. (Gaia collaboration) (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics. 616. A1. arXiv:1804.09365. Bibcode:2018A&A...616A...1G. doi:10.1051/0004-6361/201833051. Gaia DR2 record for this source at VizieR.
- Anderson, E.; Francis, Ch. (2012), "XHIP: An extended hipparcos compilation", Astronomy Letters, 38 (5): 331, arXiv:1108.4971, Bibcode:2012AstL...38..331A, doi:10.1134/S1063773712050015.
- Houk, Nancy (1979), Michigan catalogue of two-dimensional spectral types for the HD stars, 3, Ann Arbor, Michigan: Dept. of Astronomy, University of Michigan, Bibcode:1982mcts.book.....H.
- Randich, S.; et al. (August 1999), "Lithium in population I subgiants", Astronomy and Astrophysics, 348: 487–500, Bibcode:1999A&A...348..487R
- Pasinetti Fracassini, L. E.; Pastori, L.; Covino, S.; Pozzi, A. (February 2001), "Catalogue of Apparent Diameters and Absolute Radii of Stars (CADARS)", Astronomy and Astrophysics (Third ed.), 367: 521–524, arXiv:astro-ph/0012289, Bibcode:2001A&A...367..521P, doi:10.1051/0004-6361:20000451.
- "18 Sgr". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2019-03-24.
- Eggleton, P. P.; Tokovinin, A. A. (2008), "A catalogue of multiplicity among bright stellar systems", Monthly Notices of the Royal Astronomical Society, 389 (2): 869–879, arXiv:0806.2878, Bibcode:2008MNRAS.389..869E, doi:10.1111/j.1365-2966.2008.13596.x.