{{Short description|Star in the constellation Draco}} {{Starbox begin}} {{Starbox image | image = [[Image:AGDraLightCurve.png|250px]] | caption = A [[Photometric_system#Photometric_letters|blue band]] [[light curve]] for AG Draconis, spanning 123 years, adapted from Gális ''et al.'' (2015)<ref name="Gális"/> }} {{Starbox observe | epoch = J2000 | constell = [[Draco (constellation)|Draco]] | ra = {{RA|16|01|41.01257}}<ref name=GaiaDR2/> | dec = {{DEC|+66|48|10.1312}}<ref name=GaiaDR2/> | appmag_v = 7.9 - 10.3<ref name=vsx/> }} {{Starbox character | type = | class = K3 IIIep<ref name=Shenavrin2011/> + WD<ref name=Hric2014/> | b-v = {{Val|1.425|0.094}}<ref name=Anderson2012/> | u-b = | variable = [[Z Andromedae variable|Z And]]<ref name=gcvs/> }} {{Starbox astrometry | radial_v = {{Val|−147.42|0.30}}<ref name=Anderson2012/> | prop_mo_ra = −7.135<ref name=GaiaDR2/> | prop_mo_dec = −5.602<ref name=GaiaDR2/> | parallax = 0.2101 | p_error = 0.0268 | parallax_footnote = <ref name=GaiaDR2/> | absmag_v = }} {{Starbox orbit | reference = <ref name=Gális2016/> | period_unitless = 549.73 d | eccentricity = 0.06 | periastron = 2447622.28 [[Julian Date|JD]] | periarg = 359.8 | k1 = 4.67 }} {{Starbox detail | source = <ref name=Hric2014/> | component1 = AG Dra A | mass = 1.5 | radius = 35 | luminosity = | gravity = | temperature = | metal_fe = −1.3 | rotational_velocity = | age_myr = | component2 = AG Dra B | luminosity2 = ~ 10<sup>3</sup> | temperature2 = ~ 10<sup>5</sup> }} {{Starbox catalog | names={{odlist | V=AG Dra | BD=+67°922 | HIP=78512 | SAO=16931 | AAVSO=1601+67 | AG=+66° 715 }}<ref name=SIMBAD/> }} {{Starbox reference | Simbad = AG+Draconis }} {{Starbox end}}
'''AG Draconis''' is a [[binary star]] system in the northern [[constellation]] of [[Draco (constellation)|Draco]]. It consists of a [[giant star]] and a [[white dwarf]] that revolve around each other every 550 days.
== Discovery == AG Draconis has been catalogued since mid 20th century, as BD+67°922. However, its unusual nature did not start to come to light until the middle of the century. It was noted as an emission-line object in 1943,<ref name=janssen/> although its nature was not understood.<ref name=wilson1950/> The [[emission spectrum]] was serendipitously discovered to be variable by [[Nancy Grace Roman]] when she observed the star and found that the spectrum had completely changed since earlier observations.<ref name=roman/> It was given the [[variable star designation]] AG Draconis in 1964.<ref name=ibvs/>
== Variability == AG Draconis spends most of its time in a quiescent phase near [[visual magnitude]] 9.8, with only small semi-regular variations thought to be due to pulsations of the giant star. At its faintest, it can reach magnitude 10.3.<ref name=vsx/> The semi-regular variations have periods of 340 - 370 days. Variations at [[ultraviolet]] wavelengths occur with a period of 550 days, which is the orbital period.<ref name=Meinunger1979/>
Every 12-16 years, outbursts occur and last for several years.<ref name=Hric2014/> The brightness can increase to visual magnitude 7.9,<ref name=vsx/> although usually not this bright.<ref name=Hric2014/>
== System == The ''a'' sin ''i'' value for the primary is {{solar radius|50.69}}, where ''a'' is the [[semimajor axis]] and ''i'' is the (unknown) [[orbital inclination]].<ref name=Gális2016/> The larger star is thought to be an orange hued giant around 1.5 times as massive as the Sun that has swollen to around 35 times the diameter of the Sun with a spectral type measured at K3IIIep.<ref name=Hric2014/> The smaller star is a compact hot white dwarf around 0.4 times as massive as the Sun, with a surface temperature of around 80,000 K.<ref name="sion"/>
==References== <references> <ref name=ibvs>{{cite journal |bibcode=1964IBVS...73....1R |title=AG Draconis |last1=Robinson |first1=L. J. |journal=Information Bulletin on Variable Stars |year=1964 |volume=73 |pages=1 }}</ref>
<ref name=Meinunger1979>{{cite journal |bibcode=1979IBVS.1611....1M |title=Discovery of a period in the symbiotic star AG Draconis |last1=Meinunger |first1=L. |journal=Information Bulletin on Variable Stars |year=1979 |volume=1611 |pages=2 }}</ref>
<ref name=wilson1950>{{cite journal |bibcode=1950PASP...62...14W |title=The Spectrum of HD 4174 |last1=Wilson |first1=Ralph E. |journal=Publications of the Astronomical Society of the Pacific |year=1950 |volume=62 |issue=363 |pages=14 |doi=10.1086/126211 |s2cid=120390522 }}</ref>
<ref name=roman>{{cite journal|bibcode=1953ApJ...117..467R|doi=10.1086/145717|title=The Spectrum of BD+67°922|journal=The Astrophysical Journal|volume=117|pages=467|year=1953|last1=Roman|first1=Nancy G.}}</ref>
<ref name=SIMBAD>{{cite simbad | title=AG Dra | access-date=2 September 2018 }}</ref>
<ref name=GaiaDR2>{{cite DR2}}</ref>
<ref name=janssen>{{cite journal |bibcode=1943PASP...55..244J |title=A Peculiar Emission-Line Object |last1=Janssen |first1=Edith M. |last2=Vyssotsky |first2=A. N. |journal=Publications of the Astronomical Society of the Pacific |year=1943 |volume=55 |issue=326 |pages=244 |doi=10.1086/125560 |s2cid=122605688 }}</ref>
<ref name=Anderson2012>{{cite journal | title=XHIP: An extended hipparcos compilation | last1=Anderson | first1=E. | last2=Francis | first2=Ch. | journal=Astronomy Letters | arxiv=1108.4971 | volume=38 | issue=5 | pages=331 | year=2012 | bibcode=2012AstL...38..331A | doi=10.1134/S1063773712050015 | s2cid=119257644 }}</ref>
<ref name=gcvs>{{cite journal | title=General catalogue of variable stars: Version GCVS 5.1 | last1=Samus' | first1=N. N | last2=Kazarovets | first2=E. V | last3=Durlevich | first3=O. V | last4=Kireeva | first4=N. N | last5=Pastukhova | first5=E. N | journal=Astronomy Reports | volume=61 | issue=1 | pages=80 | year=2017 | doi=10.1134/S1063772917010085 | bibcode=2017ARep...61...80S | s2cid=125853869 }}</ref>
<ref name="sion">{{cite journal | display-authors=1 | last1=Sion | first1=Edward M. | last2=Moreno | first2=Jackeline | last3=Godon | first3=Patrick | last4=Sabra | first4=Bassem | last5=Mikolajewska | first5=Joanna | title=On the Nature of the Hot Component in the Symbiotic, Supersoft X-Ray Binary AG Draconis | journal=The Astronomical Journal | volume=144 | issue=6 | pages=5 | id=171 | date=2012 | doi=10.1088/0004-6256/144/6/171 | arxiv=1210.1111 | bibcode=2012AJ....144..171S | s2cid=118737620 }}</ref>
<ref name=Shenavrin2011>{{cite journal | display-authors=1 | last1=Shenavrin | first1=V. I. | last2=Taranova | first2=O. G. | last3=Nadzhip | first3=A. E. | title=Search for and study of hot circumstellar dust envelopes | journal=Astronomy Reports | volume=55 | issue=1 | pages=31–81 | date=2011 | bibcode=2011ARep...55...31S | doi=10.1134/S1063772911010070 | s2cid=122700080 }}</ref>
<ref name="Gális">{{cite journal |last1=Gális |first1=R. |last2=Hric |first2=L. |last3=Smelcer |first3=L. |title=AG Draconis - a symbiotic mystery |journal=Open European Journal on Variable Stars |date=February 2015 |volume=169 |pages=4–9 |bibcode=2015OEJV..169....4G |url=https://ui.adsabs.harvard.edu/abs/2015OEJV..169....4G |access-date=2 January 2022}}</ref>
<ref name=Gális2016>{{cite journal |bibcode=1999A&A...348..533G |title=Resonances as the general cause of the outbursts in the symbiotic system AG Draconis |last1=Gális |first1=R. |last2=Hric |first2=L. |last3=Friedjung |first3=M. |last4=Petrík |first4=K. |journal=Astronomy and Astrophysics |year=1999 |volume=348 |pages=533 }}</ref>
<ref name=Hric2014>{{cite journal | title=Outburst activity of the symbiotic system AG Dra | display-authors=1 | last1=Hric | first1=L. | last2=Gális | first2=R. | last3=Leedjärv | first3=L. | last4=Burmeister | first4=M. | last5=Kundra | first5=E. | journal=Monthly Notices of the Royal Astronomical Society | volume=443 | issue=2 | pages=1103–1112 | date=September 2014 | doi=10.1093/mnras/stu1162 | doi-access=free | bibcode=2014MNRAS.443.1103H | arxiv=1406.5505 | s2cid=119225658 }}</ref>
<ref name=vsx>{{cite web |url=https://www.aavso.org/vsx/index.php?view=detail.top&oid=13733 |title=AG Draconis |website=Variable Star Index |publisher=[[AAVSO]] |access-date=2020-04-29 }}</ref> </references>
{{Stars of Draco}}
[[Category:K-type giants]] [[Category:Emission-line stars]] [[Category:White dwarfs]] [[Category:Z Andromedae variables]] [[Category:Spectroscopic binaries]] [[Category:Draco (constellation)]] [[Category:Durchmusterung objects]] [[Category:Hipparcos objects|078512]] [[Category:Objects with variable star designations|Draconis, AG]]