View source for Astronomy:HD 203857

{{short description|Double star in the constellation Cygnus}}
{{Starbox begin}}
{{Starbox observe
 | epoch       = [[Astronomy:J2000.0|J2000.0]]
 | constell    = [[Astronomy:Cygnus (constellation)|Cygnus]]
 | ra          = {{RA|21|23|48.38864}}<ref name=GaiaDR2/>
 | dec         = {{DEC|+37|21|05.3177}}<ref name=GaiaDR2/>
 | appmag_v    = 6.46<ref name=Anderson2012/>
}}
{{Starbox character
 | type        = 
 | class       = K5<ref name=Hoffleit1991/>
 | b-v         = {{Val|1.472|0.006}}<ref name=Anderson2012/>
 | u-b         = 
 | variable    = 
}}
{{Starbox astrometry
 | radial_v    = {{Val|−6.26|0.16}}<ref name=GaiaDR2/>
 | prop_mo_ra  = −5.999<ref name=GaiaDR2/>
 | prop_mo_dec = −8.364<ref name=GaiaDR2/>
 | parallax    = 2.6601
 | p_error     = 0.0417
 | parallax_footnote = <ref name=GaiaDR2/>
 | absmag_v    = −0.75<ref name=Anderson2012/>
}}
{{Starbox detail 
 | source      = <ref name=Toyota2009 />
 | mass        = 1.7 
 | radius      = 46-50
 | luminosity  = 513
 | temperature = 4,080
}}
{{Starbox catalog 
 | names = {{odlist | BD=+36°4543 | HD=203857 | HIP=105637 | HR=8193 | SAO=71280 | CCDM=J21237+3722A }}<ref name=SIMBAD/> 
}}
{{Starbox reference
 | Simbad = HD+203857
}}
{{Starbox end}}

'''HD 203857''' is a [[Astronomy:Double star|double star]] in the [[Astronomy:Constellation|constellation]] [[Astronomy:Cygnus (constellation)|Cygnus]]. It is near the lower limit of visibility to the naked eye, having a combined [[Astronomy:Apparent visual magnitude|apparent visual magnitude]] of 6.46.<ref name=Anderson2012/> The distance to the primary component is approsimatly 1,230&nbsp;[[Light year|light year]]s based on [[Astronomy:Stellar parallax|parallax]], and it has an [[Astronomy:Absolute magnitude|absolute magnitude]] of −0.75.<ref name=Anderson2012/> The star is drifting closer to the [[Astronomy:Sun|Sun]] with a [[Astronomy:Radial velocity|radial velocity]] of −6.3&nbsp;km/s.<ref name=GaiaDR2/> It has a [[Astronomy:Stellar classification|stellar classification]] of K5<ref name=Hoffleit1991/> and is known to be [[Astronomy:Stellar evolution|evolved]].  The star likely hosts an extrasolar planet, though yet unconfirmed.

HD 203857 is listed in the Washington Double Star Catalogue as having five [[Astronomy:Visual binary|visual companions]].  It is separated by six arc-minutes from HD 203784, an [[Astronomy:F-type star|F-type]] [[Astronomy:Subgiant|subgiant]], though it is likely they are actually not gravitationally–bound.<ref name=Toyota2009/>  HD 203784 is thought to be closer to us and less luminous than HD 203857.<ref name=dr2b/>  There are also fainter stars at {{val|23|ul="}} and {{val|178|u="}}.  HD 203784 has a 13th-magnitude star and a 14th-magnitude star within {{val|20|u="}}.<ref name=wds/>

==Substellar companion==

[[Astronomy:Okayama Planet Search Program|Okayama Planet Search]] team has published a paper in late 2008 reporting investigations on radial velocity variations observed for a set of evolved stars, announcing possible detection of a substellar companion orbiting the giant star HD 203857.<ref name=Toyota2009/> [[Astronomy:Orbital period|Orbital period]] is estimated 2.3 years, but planet has still to be confirmed.

{{OrbitboxPlanet begin}}
{{OrbitboxPlanet hypothetical
 | exoplanet = b
 | mass = ≥8.1
 | period = 836.8
 | semimajor = 2.1
 | eccentricity = 0.3
}}
{{Orbitbox end}}

==References==
{{reflist|refs=

<ref name=GaiaDR2>{{cite DR2|1963812021591567872}}</ref>

<ref name=dr2b>{{cite DR2|1964001000151278080}}</ref>

<ref name=SIMBAD>{{cite simbad | title=HD 203857 | access-date=2020-03-09}}</ref>

<ref name=Anderson2012>{{citation
 | 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 | postscript=.
 | doi=10.1134/S1063773712050015 | s2cid=119257644 }}</ref>

<ref name=Toyota2009>{{citation | postscript=.
 | title=Radial Velocity Search for Extrasolar Planets in Visual Binary Systems
 | last1=Toyota | first1=Eri | last2=Itoh | first2=Yoichi
 | last3=Ishiguma | first3=Shinichiro | last4=Urakawa | first4=Seitaro
 | last5=Murata | first5=Daisuke | last6=Oasa | first6=Yumiko
 | last7=Matsuyama | first7=Hiroko | last8=Funayama | first8=Hitoshi
 | last9=Sato | first9=Bun'ei | last10=Mukai | first10=Tadashi
 | display-authors=1 | journal=Publications of the Astronomical Society of Japan
 | volume=61 | issue=1 | pages=19–28 | date=February 2009
 | doi=10.1093/pasj/61.1.19 | bibcode=2009PASJ...61...19T | doi-access=free | hdl=20.500.14094/90001422 | hdl-access=free }}</ref>

<ref name=Hoffleit1991>{{citation
 | last1=Hoffleit | first1=Dorrit | last2=Jaschek | first2=Carlos
 | title=The Bright star catalogue
 | location=New Haven, Conn. | postscript=.
 | publisher=Yale University Observatory
 | edition=5th Revised | year=1991
 | bibcode=1991bsc..book.....H }}</ref>

<ref name=wds>{{citation |bibcode=1967ApJ...150..115F |title=Type I Supernovae |last1=Finzi |first1=A. |last2=Wolf |first2=R. A. |journal=The Astrophysical Journal |volume=150 |pages=115 |year=1967 |doi=10.1086/149317 |postscript=. |doi-access=free }}</ref>

}}

==External links==
* [http://exoplanet.eu/star.php?st=HD%20203857 ]{{dead link|date=December 2023|bot=medic}}{{cbignore|bot=medic}}

{{Stars of Cygnus}}

[[Category:K-type giants]]
[[Category:Hypothetical planetary systems]]
[[Category:Double stars]]
[[Category:Cygnus (constellation)]]
[[Category:Durchmusterung objects]]
[[Category:Henry Draper Catalogue objects|203857]]
[[Category:Hipparcos objects|105637]]
[[Category:Bright Star Catalogue objects|8193]]

{{Sourceattribution|HD 203857}}