18 Draconis
18 Draconis is a likely binary star[7] system in the northern circumpolar constellation of Draco. With an apparent visual magnitude of 4.84,[2] it is just bright enough to be faintly visible to the naked eye. The distance to this system, as estimated from an annual parallax shift of 4.5 mas,[1] is roughly 720 light years. It is moving closer to the Sun with a heliocentric radial velocity of −1.4 km/s,[4] and is a probable member of the Sirius stream of co-moving stars.[8]
 18 Draconis in optical light | |
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Draco |
| Right ascension | 16h 40m 55.11952s[1] |
| Declination | +64° 35′ 20.5824″[1] |
| Apparent magnitude (V) | 4.84[2] |
| Characteristics | |
| Spectral type | K0 III CN−0.5 CH−2 Ca1[3] |
| B−V color index | 1.212±0.003[2] |
| Astrometry | |
| Radial velocity (Rv) | −1.37±0.09[4] km/s |
| Proper motion (μ) | RA: −0.599[1] mas/yr Dec.: −17.436[1] mas/yr |
| Parallax (π) | 4.5045 ± 0.1730[1] mas |
| Distance | 720 ± 30 ly (222 ± 9 pc) |
| Absolute magnitude (MV) | −1.92[2] |
| Details[5] | |
| Mass | 3.81±0.38 M☉ |
| Radius | 46.83±1.74 R☉ |
| Luminosity | 786.7±56.3 L☉ |
| Surface gravity (log g) | 1.69±0.06 cgs |
| Temperature | 4,471±23 K |
| Metallicity [Fe/H] | −0.13±0.10 dex |
| Age | 280±80 Myr |
| Other designations | |
| Database references | |
| SIMBAD | data |
The visible component has a stellar classification of K0 III CN−0.5 CH−2 Ca1,[3] indicating it is an evolved K-type giant star with some abundance peculiarities in its atmosphere. At the age of around 280 million years, it is most likely (99% chance) on the horizontal branch.[5] It is a barium star, which suggests it may have a degenerate white dwarf companion from which it accreted materials during an earlier stage of its evolution.[9][7] 18 Dra has an estimated 3.8 times the mass of the Sun and has expanded to 47 times the Sun's radius. The star is radiating 787 times the Sun's luminosity from its enlarged photosphere at an effective temperature of 4,471 K.[5]
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.
- 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.
- Keenan, Philip C.; McNeil, Raymond C. (1989), "The Perkins catalog of revised MK types for the cooler stars", Astrophysical Journal Supplement Series, 71: 245, Bibcode:1989ApJS...71..245K, doi:10.1086/191373.
- de Bruijne, J. H. J.; Eilers, A.-C. (October 2012), "Radial velocities for the HIPPARCOS-Gaia Hundred-Thousand-Proper-Motion project", Astronomy & Astrophysics, 546: 14, arXiv:1208.3048, Bibcode:2012A&A...546A..61D, doi:10.1051/0004-6361/201219219, A61.
- Reffert, Sabine; et al. (2015), "Precise radial velocities of giant stars. VII. Occurrence rate of giant extrasolar planets as a function of mass and metallicity", Astronomy & Astrophysics, 574: A116, arXiv:1412.4634, Bibcode:2015A&A...574A.116R, doi:10.1051/0004-6361/201322360, hdl:10722/215277.
- "g Dra". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2018-07-17.
- 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, arXiv:0806.2878, Bibcode:2008MNRAS.389..869E, doi:10.1111/j.1365-2966.2008.13596.x.
- Famaey, B.; et al. (2005), "Local kinematics of K and M giants from CORAVEL/Hipparcos/Tycho-2 data. Revisiting the concept of superclusters", Astronomy and Astrophysics, 430: 165–186, arXiv:astro-ph/0409579, Bibcode:2005A&A...430..165F, doi:10.1051/0004-6361:20041272.
- Gomez, A. E.; et al. (1997), "Absolute magnitudes and kinematics of barium stars", Astronomy and Astrophysics, 319: 881, Bibcode:1997A&A...319..881G.
