18 Draconis
{{Short description|Star in the constellation Draco}}
{{Starbox begin
| name = 18 Draconis
}}
{{Starbox image
| image = 300px
| caption = 18 Draconis in optical light
}}
{{Starbox observe
| epoch = J2000
| constell = Draco
| dec = {{DEC|+64|35|20.5824}}
}}
{{Starbox character
| type = horizontal branch
| class = {{nowrap|K0 III CN−0.5 CH−2 Ca1}}
| u-b =
}}
{{Starbox astrometry
| radial_v = {{Val|−1.37|0.09}}
| parallax = 4.5045
| p_error = 0.1730
}}
{{Starbox detail
| mass = {{Val|3.81|0.38}}
| radius = {{Val|46.83|1.74}}
| luminosity = {{Val|786.7|56.3}}
| gravity = {{Val|1.69|0.06}}
| temperature = {{Val|4471|23|fmt=commas}}
| metal_fe = {{Val|−0.13|0.10}}
| rotational_velocity =
| age_myr = {{Val|280|80}}
}}
{{Starbox catalog
| names = {{odlist | B=g Dra | F=18 Dra | BD=+64°1145 | FK5=3326 | HD=151101 | HIP=81660 | HR=6223 | SAO=17188 }}
}}
{{Starbox reference
| Simbad = g+Dra
}}
{{Starbox end}}
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 {{Val|4.5|ul=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 {{nowrap|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
{{reflist|refs=
{{cite simbad | title=g Dra | access-date=2018-07-17 }}
| display-authors=1 | last1=Reffert | first1=Sabine
| last2=Bergmann | first2=Christoph | last3=Quirrenbach | first3=Andreas
| last4=Trifonov | first4=Trifon | last5=Künstler | first5=Andreas
| title=Precise radial velocities of giant stars. VII. Occurrence rate of giant extrasolar planets as a function of mass and metallicity
| journal=Astronomy & Astrophysics
| volume=574 | pages=A116 | year=2015
| bibcode=2015A&A...574A.116R | doi=10.1051/0004-6361/201322360
| arxiv=1412.4634 | postscript=. | hdl=10722/215277| s2cid=59334290 }}
| last1=de Bruijne | first1=J. H. J. | last2=Eilers | first2=A.-C.
| title=Radial velocities for the HIPPARCOS-Gaia Hundred-Thousand-Proper-Motion project
| journal=Astronomy & Astrophysics
| volume=546 | id=A61 | pages=14 | date=October 2012
| doi=10.1051/0004-6361/201219219 | bibcode=2012A&A...546A..61D
| arxiv=1208.3048 | s2cid=59451347 | postscript=. }}
| title=A catalogue of multiplicity among bright stellar systems
| last1=Eggleton | first1=P. P. | last2=Tokovinin | first2=A. A.
| journal=Monthly Notices of the Royal Astronomical Society
| volume=389 | issue=2 | pages=869 | date=2008
| doi=10.1111/j.1365-2966.2008.13596.x | doi-access=free | postscript=.
| bibcode=2008MNRAS.389..869E | arxiv=0806.2878 | s2cid=14878976 }}
| display-authors=1 | last1=Gomez | first1=A. E.
| last2=Luri | first2=X. | last3=Grenier | first3=S.
| last4=Prevot | first4=L. | last5=Mennessier | first5=M. O.
| last6=Figueras | first6=F. | last7=Torra | first7=J.
| title=Absolute magnitudes and kinematics of barium stars
| journal=Astronomy and Astrophysics
| volume=319 | pages=881 | year=1997
| bibcode=1997A&A...319..881G | postscript=. }}
| display-authors=1 | last1=Famaey | first1=B.
| last2=Jorissen | first2=A. | last3=Luri | first3=X.
| last4=Mayor | first4=M. | last5=Udry | first5=S.
| last6=Dejonghe | first6=H. | last7=Turon | first7=C.
| title=Local kinematics of K and M giants from CORAVEL/Hipparcos/Tycho-2 data. Revisiting the concept of superclusters
| journal=Astronomy and Astrophysics
| volume=430 | pages=165–186 | date=2005
| doi=10.1051/0004-6361:20041272 | bibcode=2005A&A...430..165F
| postscript=. | arxiv=astro-ph/0409579 | s2cid=17804304 }}
| title=The Perkins catalog of revised MK types for the cooler stars
| journal=Astrophysical Journal Supplement Series
| volume=71 | pages=245 | year=1989
| last1=Keenan | first1=Philip C. | last2=McNeil | first2=Raymond C.
| bibcode=1989ApJS...71..245K | doi=10.1086/191373 | s2cid=123149047
}}
| title=XHIP: An extended hipparcos compilation
| last1=Anderson | first1=E. | last2=Francis | first2=Ch.
| journal=Astronomy Letters
| volume=38 | issue=5 | pages=331 | year=2012
| bibcode=2012AstL...38..331A | doi=10.1134/S1063773712050015
| arxiv=1108.4971 | s2cid=119257644 | postscript=. }}
}}
{{Stars of Draco}}
{{DEFAULTSORT:18 Draconis}}
Category:Draco (constellation)