{{Short description|Binary star system in the constellation Draco}} {{Starbox begin | name = β Draconis }} {{Starbox image | image = {{Location mark |image=Draco constellation map.svg|alt=|float=center|width=240 |label=|position=right |mark=Red circle.svg|mark_width=10|mark_link=β Dra |x=290|y=968 }} | caption = Location of β Draconis (circled) }} {{Starbox observe | epoch = [[J2000.0]] | equinox = [[J2000.0]] ([[International Celestial Reference System|ICRS]]) | constell = [[Draco (constellation)|Draco]] | ra = {{RA|17|30|25.96170}}<ref name=aaa474_2_653/> | dec = {{DEC|+52|18|04.9993}}<ref name=aaa474_2_653/> | appmag_v = 2.79<ref name=mnras402_2_1369/> }} {{Starbox character | type = | class = G2Ib-IIa<ref name=keenan1980/> | u-b = {{val|+0.954|0.007}}<ref name=Anderson_Francis_2012/> | b-v = +0.98<ref name=bsc1 /> | r-i = +0.48<ref name=bsc1 /> | variable = }} {{Starbox astrometry | radial_v = {{val|−21.00|0.23}}<ref name=Anderson_Francis_2012/> | prop_mo_ra = −15.89<ref name=aaa474_2_653/> | prop_mo_dec = +12.28<ref name=aaa474_2_653/> | parallax = 8.58 | p_error = 0.10 | parallax_footnote = <ref name=aaa474_2_653/> | absmag_v = –2.457<ref name=katz2011/> }} {{Starbox detail | mass = {{val|6.0|0.2}}<ref name=mnras402_2_1369/> | radius = 40<ref name=mcdonald2017/> | luminosity = 996<ref name=mcdonald2017/> | temperature = {{val|5160|150|fmt=commas}}<ref name=Marfil_et_al_2020/> | gravity = {{val|1.86|0.04}}<ref name=Marfil_et_al_2020/> | metal_fe = {{val|0.02|0.10}}<ref name=Marfil_et_al_2020/> | age_myr = 65<ref name=mnras402_2_1369/> | rotational_velocity = 10.7<ref name=Marfil_et_al_2020/> }} {{Starbox catalog | names = {{odlist | name=Rastaban | name2=Rastaben | name3=Alwaid | name4=Asuia | name5=NGCA-V25 | B=β Dra | F=23 Dra | BD=+52°2065 | FK5=653 | HD=159181 | HIP=85670 | HR=6536 | SAO=30429 | ADS=10611 | WDS=17304+5218AB }}<ref name=SIMBAD /> }} {{Starbox reference | Simbad=bet+dra }} {{Starbox end}}
'''Beta Draconis''' ('''β Draconis''', abbreviated '''Beta Dra''', '''β Dra''') is a [[binary star]] system<ref name=Eggleton_Tokovinin_2008/> and the third-brightest [[star]] in the northern [[circumpolar constellation]] of [[Draco (constellation)|Draco]]. The two components are designated Beta Draconis A (officially named '''Rastaban''' {{IPAc-en|'|r|æ|s|t|@|b|æ|n}}, the traditional name of the system)<ref name="IAU-LSN"/> and B respectively. With a combined [[apparent visual magnitude]] of 2.79,<ref name=mnras402_2_1369/> it is bright enough to be [[Bortle Dark-Sky Scale|easily seen]] with the naked eye. Based upon [[stellar parallax|parallax]] measurements from the [[Hipparcos]] astrometry satellite,<ref name=aaa323_L49/><ref name=GSM/> it lies at a distance of about {{Convert|380|ly|pc|abbr=off|lk=on}} from the [[Sun]].<ref name=aaa474_2_653/> The system is drifting closer with a [[radial velocity]] of −21 km/s.<ref name=Anderson_Francis_2012/>
The binary system consists of a [[bright giant]] orbited by a [[main-sequence star|dwarf]] companion once every four [[millennia]] or so.<ref name=kaler /> The companion is about 11 magnitudes fainter than the primary star,<ref name=wds/> and the two are separated by {{val|4.2|ul="}}.<ref name=Eggleton_Tokovinin_2008/>
The [[stellar spectrum|spectrum]] of the primary, Beta Draconis A, matches a [[stellar classification]] of G2Ib-IIa,<ref name=keenan1980/> showing mixed features of a [[bright giant]] and a [[supergiant star]], and is listed as a standard star for that spectral class.<ref name=perkins/> It is about 65 million years old<ref name=mnras402_2_1369/> and is currently undergoing its first convective [[dredge-up]].<ref name=Kovtyukh_et_al_2005/> Compared to the Sun, Beta Draconis A is an enormous star with six times [[Solar mass|the mass]] and roughly 40 times [[Solar radius|the radius]]. At this size, it is emitting about 950 times the [[solar luminosity|luminosity of the Sun]] from its outer envelope at an [[effective temperature]] of 5,160 [[Kelvin|K]],<ref name=mnras402_2_1369/> giving it the yellow hue of a [[Stellar classification#Class G|G-type star]].<ref name=csiro/> The star has a particularly strong [[chromospheric activity|chromospheric emission]] that is generating [[X-ray astronomy|X-ray]]<ref name=Evans_et_al_2010/><ref name=Skinner_Brown_1996/> and [[Ultraviolet astronomy|far-UV]] radiation.<ref name=Brown_et_al_1984/> There is a detectable [[stellar magnetic field|magnetic field]] with a longitudinal field strength of {{val|−1.16|0.25|ul=G}}.<ref name=Grunhut_et_al_2010/>
Beta Draconis lies on or near the [[cepheid instability strip]],<ref name=Butler1998/> yet only appears to be a microvariable with a range of about 1/100 of a magnitude.<ref name=ricker2014/><ref name=perryman1997/> It was confirmed as a variable star with a range of about 1/100 of a magnitude by Gabriel Cristian Neagu using data from the TESS and Hipparcos missions.<ref name=ricker2014/><ref name=perryman1997/> The variability was reported to the AAVSO (American Association of Variable Star Observers), in the Variable Star Index.<ref name=vsx/>
==Nomenclature== ''β Draconis'' ([[Latinisation of names|Latinised]] to ''Beta Draconis'') is the system's [[Bayer designation]]. The designations of the two components as ''Beta Draconis A'' and ''B'' derive from the convention used by the Washington Multiplicity Catalog (WMC) for [[Star system|multiple star system]]s, and adopted by the [[International Astronomical Union]] (IAU).<ref name="planetnaming"/>
It bore the traditional name ''Rastaban'', which has also been used for [[Gamma Draconis]].<ref name=kaler/><ref name=allen/> This name, less commonly written ''Rastaben'', derives from the [[Arabic]] phrase ''ra's ath-thu'ban'' "head of the serpent/dragon". It was also known as ''Asuia'' and ''Alwaid'' {{IPAc-en|æ|l|'|w|ei|d}},<ref name=Kunitzsch/> the latter from the Arabic ''al-ʽawāʼidh'' "the old mother camels".<ref name=Kunitzsch/> In 2016, the IAU organized a [[IAU Working Group on Star Names|Working Group on Star Names]] (WGSN)<ref name="WGSN"/> to catalogue and standardize proper names for stars. The WGSN approved the name ''Rastaban'' for the component Beta Draconis A on 21 August 2016 and it is now so included in the List of IAU-approved Star Names.<ref name="IAU-LSN"/>
Beta Draconis is part of the [[asterism (astronomy)|asterism]] of the [[Mother Camels]] (Arabic ''al'awa'id''), along with Gamma Draconis (Eltanin), [[Mu Draconis]] (Alrakis), [[Nu Draconis]] (Kuma) and [[Xi Draconis]] (Grumium), which was later known as the ''Quinque Dromedarii''.<ref name=allen/>
In [[Chinese astronomy|Chinese]], {{lang|zh|天棓}} ({{lang|zh-Latn|Tiān Bàng}}), meaning ''[[Purple Forbidden enclosure|Celestial Flail]]'', refers to an asterism consisting of Beta Draconis, Xi Draconis, Nu Draconis, Gamma Draconis and [[Iota Herculis]].<ref name=zh/> Consequently, the [[Chinese star names|Chinese name]] for Beta Draconis itself is known as {{lang|zh|天棓三}} ({{lang|zh-Latn|Tiān Bàng sān}}, {{langx|en|the Third Star of Celestial Flail}}).<ref name=allen /><ref name=lcsd/><ref name=words/>
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==External links== * {{cite book | last=Dibon-Smith | first=Richard | date=1992 | title=StarList 2000: A Quick Reference Star Catalog for Astronomers | publication-place=New York | publisher=John Wiley & Sons | bibcode=1992sqrs.book.....D | isbn=0-471-55895-8 }}
{{Stars of Draco}} {{Authority control}}
[[Category:G-type bright giants]] [[Category:G-type supergiants]] [[Category:Binary stars]] [[Category:Draco (constellation)]] [[Category:Bayer objects|Draconis, Beta]] [[Category:Durchmusterung objects|BD+52 2065]] [[Category:Flamsteed objects|Draconis, 23]] [[Category:Henry Draper Catalogue objects|159181]] [[Category:Hipparcos objects|085670]] [[Category:Bright Star Catalogue objects|6536]] [[Category:Stars with proper names|Rastaban]] [[Category:Population I stars]]