18 Draconis

Star in the constellation Draco Draco constellation map.svg center 280 right Red circle.svg 10 18 Dra 472 718 Location of 18 Dra (circled in red) J2000 Draco 16 40 55.11952 +64 35 20.5824 4.84 horizontal branch K0 III CN−0.5 CH−2 Ca1 1.212 0.003 −1.37 0.09 −0.599 −17.436 4.5045 0.1730 −1.92 3.81 0.38 46.83 1.74 786.7 56.3 1.69 0.06 4471 23 commas −0.13 0.10 280 80 g Dra 18 Dra +64°1145 3326 151101 81660 6223 17188 g+Dra thumb|left|18 Draconis in optical light 18 Draconis is a likely binary star system in the northern circumpolar constellation of Draco. With an apparent visual magnitude of 4.84, 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, is roughly 720 light years (220 parsecs). It is moving closer to the Sun with a heliocentric radial velocity of −1.4 km/s, and is a probable member of the Sirius stream of co-moving stars. The visible component has a stellar classification of K0 III CN−0.5 CH−2 Ca1, 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. 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. 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. References g Dra 2018-07-17 1 Reffert Sabine Bergmann Christoph Quirrenbach Andreas Trifonov Trifon Künstler Andreas Precise radial velocities of giant stars. VII. Occurrence rate of giant extrasolar planets as a function of mass and metallicity Astronomy & Astrophysics 574 A116 2015 2015A&A...574A.116R 10.1051/0004-6361/201322360 1412.4634 . 10722/215277 59334290 de Bruijne J. H. J. Eilers A.-C. Radial velocities for the HIPPARCOS-Gaia Hundred-Thousand-Proper-Motion project Astronomy & Astrophysics 546 A61 14 October 2012 10.1051/0004-6361/201219219 2012A&A...546A..61D 1208.3048 59451347 . A catalogue of multiplicity among bright stellar systems Eggleton P. P. Tokovinin A. A. Monthly Notices of the Royal Astronomical Society 389 2 869 2008 10.1111/j.1365-2966.2008.13596.x free . 2008MNRAS.389..869E 0806.2878 14878976 1 Gomez A. E. Luri X. Grenier S. Prevot L. Mennessier M. O. Figueras F. Torra J. Absolute magnitudes and kinematics of barium stars Astronomy and Astrophysics 319 881 1997 1997A&A...319..881G . 1 Famaey B. Jorissen A. Luri X. Mayor M. Udry S. Dejonghe H. Turon C. Local kinematics of K and M giants from CORAVEL/Hipparcos/Tycho-2 data. Revisiting the concept of superclusters Astronomy and Astrophysics 430 165–186 2005 10.1051/0004-6361:20041272 2005A&A...430..165F . astro-ph/0409579 17804304 . The Perkins catalog of revised MK types for the cooler stars Astrophysical Journal Supplement Series 71 245 1989 Keenan Philip C. McNeil Raymond C. 1989ApJS...71..245K 10.1086/191373 123149047 XHIP: An extended hipparcos compilation Anderson E. Francis Ch. Astronomy Letters 38 5 331 2012 2012AstL...38..331A 10.1134/S1063773712050015 1108.4971 119257644 . Category:Barium stars Category:Binary stars Category:Draco (constellation) Draconis, g Category:Durchmusterung objects Draconis, 18 151101 081660 6223 Category:Horizontal-branch stars Category:K0III stars