{{Short description|Double star in the constellation Draco}} {{Starbox begin | name = KOI-256 }} {{Starbox image | image = [[File:Dead Star Acts Like Magnifying Glass.jpg|270px]] | caption = Artist's impression of the white dwarf companion gravitationally bending the starlight of KOI-256 }} {{Starbox observe | epoch = [[J2000]] | constell = [[Draco (constellation)|Draco]]<ref name=constellation/> | ra = {{RA|19|00|44.42489}}<ref name="GaiaDR3"/> | dec = {{DEC|+49|33|55.2489}}<ref name="GaiaDR3"/> }} {{Starbox character | component1 = KOI-256 A | type = [[Red dwarf]] | class = [[Stellar classification#Class M|M3V]] | appmag_1_passband = Kepler | appmag_1 = 15.37 | appmag_2_passband = J | appmag_2 = {{val|12.701|0.024}} | appmag_3_passband = H | appmag_3 = {{val|12.001|0.019}} | appmag_4_passband = Ks | appmag_4 = {{val|11.783|0.023}} | appmag_5_passband = r | appmag_5 = 15.754 | appmag_6_passband = i | appmag_6 = 14.636 | appmag_7_passband = z | appmag_7 = 14.059 | r-i = 1.118 | v-r = <!--V−R color--> | b-v = <!--B−V color--> | u-b = <!--U−B color--> | j-h = {{val|0.700|0.031}} | j-k = {{val|0.918|0.033}} | component2 = KOI-256 B | type2 = [[White dwarf]] | class2 = [[Stellar classification#Class D|D]] | appmag_1_passband2 = Kepler | appmag_1_2 = 19.45 }} {{Starbox astrometry | prop_mo_ra = {{val|-6.796|0.030}} | prop_mo_dec = {{val|-14.373|0.030}} | pm_footnote = <ref name="GaiaDR3"/> | parallax = 5.6681 | p_error = 0.0228 | parallax_footnote = <ref name="GaiaDR3"/> }} {{Starbox orbit | reference = <ref name="Muirhead2013"/> | name = KOI-256 B | period_unitless = {{val|1.3786548|0.00001|fmt=none|u=days}} | axis_unitless = {{val|0.0250|0.0018|ul=AU}} | eccentricity = 0 | inclination = {{val|89.01|0.65}} | periastron = {{val|2455373.635498|0.000036|fmt=none}} | periarg_primary = 90 | k1 = {{val|106.5|1.8}} }} {{Starbox detail | source = <ref name="Muirhead2013"/> | component1 = KOI-256 A | mass = {{val|0.51|0.15}} | radius = {{val|0.54|0.014}} | temperature = {{val|3450|50}} | metal = {{val|+0.31|0.10}} | rotational_velocity = {{val|19.79|0.52}} | component2 = KOI-256 B | mass2 = {{val|0.592|0.084}} | radius2 = {{val|0.01345|0.00091}} | temperature2 = {{val|7100|800}} }} {{Starbox catalog | names = {{nowrap|[[Kepler Input Catalog|KIC]] 11548140}}, {{nowrap|[[2MASS]] J19004443+4933553}} }} {{Starbox reference | Simbad = KOI-256 | NSTED = KOI-256 | KIC = 11548140 }} {{Starbox end}}
'''KOI-256''' is a [[double star]] located in the constellation [[Draco (constellation)|Draco]] approximately {{convert|575|ly|pc|lk=on}} from Earth.<ref name="GaiaDR3"/> While observations by the [[Kepler (spacecraft)|''Kepler'']] spacecraft suggested the system contained a gas giant [[exoplanet]] orbiting a [[red dwarf]], later studies determined that KOI-256 was a binary system composed of the red dwarf orbiting a [[white dwarf]].<ref name="nasa20130404"/><ref name="discover20130404"/>
==Name== [[File:White Dwarfs - Small and Strong.jpg|thumb|left|KOI-256]]
The acronym "KOI" comes from ''[[Kepler object of interest]]'' and means that the object has been cataloged by the ''[[Kepler (spacecraft)|Kepler]]'' spacecraft during its search for extrasolar planets using the [[transit method]]. The "256" is the number of the object.
==Characteristics== [[File:KOI-256LightCurve.png|thumb|left|A [[light curve]] for KOI-256, plotted from ''Kepler'' data.<ref name="MAST"/> The inset plot (adapted from Muirhead ''et al.''<ref name="Muirhead2013"/>) shows the time near the occultation of the white dwarf.]] Initial observations by the ''Kepler'' spacecraft suggested a central [[red dwarf]] with a mass of {{solar mass|0.65|link=yes}}, a radius of {{solar radius|1.1|link=yes}}, and a temperature of {{convert|3639|K|C F|lk=on}}. Its candidate [[exoplanet]] was estimated to have a mass of {{Earth mass|sym=y|14.8|link=yes}}, a radius of {{Earth radius|25.34|link=yes}}, an orbital period of 1.38 days, a temperature of {{convert|1160|K|C F}}, and a [[semi-major axis]] of 0.021 [[astronomical unit]]s.<ref name="Borucki2011"/><ref name="Szabo2013"/> Further studies by Muirhead ''et al.'' (2012) refined the candidate exoplanet parameters to a radius of {{Earth radius| {{val|5.60|0.76}} }}, a temperature of {{convert|726|K|C F}}, and a semi-major axis of 0.016 AU.<ref name="Muirhead2012"/>
Muirhead ''et al.'' (2013) performed additional observations with the [[Hale Telescope]] at [[Palomar Observatory]]. Using the [[doppler spectroscopy|radial velocity method]] for exoplanet detection, Muirhead's team found that the red dwarf was wobbling too much to be caused by a [[planetary mass object]], and was more likely being influenced by a [[white dwarf]]. Using ultraviolet data from the [[GALEX]] spacecraft, it was seen that the red dwarf was significantly active, further suggesting perturbations by a white dwarf. The team re-analyzed ''Kepler''{{'s}} data, and found that when the white dwarf passed in front of the red dwarf, the red dwarf's light noticeably warped and brightened, an effect called [[gravitational lens]]ing. While only being slightly larger than the Earth, the white dwarf has such large mass that the physically larger red dwarf orbits around its smaller companion.<ref name="nasa20130404"/>
With the new observations, the red dwarf was shown to have a mass of {{Solar mass| {{val|0.51|0.15}} }}, a radius of {{Solar radius| {{val|0.540|0.014}} }}, and a temperature of {{convert|3450|±|50|K|C F|-1}}. The white dwarf has a mass of {{Solar mass| {{val|0.592|0.084}} }}, a radius of {{Solar radius| {{val|0.01345|0.00091}} }}, and a temperature of {{convert|7100|±|800|K|C F|-2}}.<ref name="Muirhead2013"/>
==References== <references> <ref name="GaiaDR3">{{Cite Gaia DR3|2132027576829358208}}</ref>
<ref name=constellation>{{cite constellation|KOI-256}}</ref>
<ref name="nasa20130404">{{cite news | url=http://www.nasa.gov/mission_pages/kepler/news/kepler20130404.html | title=Gravity-Bending Find Leads to Kepler Meeting Einstein |publisher=[[NASA]] |date=4 April 2013 | access-date=29 August 2015 | url-status=dead | archive-url=https://web.archive.org/web/20150705131007/http://www.nasa.gov/mission_pages/kepler/news/kepler20130404.html | archive-date=5 July 2015 }}</ref>
<ref name=MAST>{{cite web | title=MAST: Barbara A. Mikulski Archive for Space Telescopes | url=https://mast.stsci.edu/portal/Mashup/Clients/Mast/Portal.html | publisher=Space Telescope Science Institute | access-date=27 August 2024}}</ref>
<ref name="discover20130404">{{cite news | url=http://news.discovery.com/space/alien-life-exoplanets/kepler-watches-white-dwarfs-gravity-warp-spacetime-13040.htm | title=Kepler Watches White Dwarf Warp Spacetime | work=[[Discovery.com]] | first=Ian | last=O'Neill | date=4 April 2013 | access-date=29 August 2015 | archive-date=15 September 2015 | archive-url=https://web.archive.org/web/20150915004704/http://news.discovery.com/space/alien-life-exoplanets/kepler-watches-white-dwarfs-gravity-warp-spacetime-13040.htm | url-status=dead }}</ref>
<ref name="Borucki2011">{{cite journal | title=Characteristics of Planetary Candidates Observed by ''Kepler''. II. Analysis of the First Four Months of Data | journal=[[The Astrophysical Journal]] | first1=William J. | last1=Borucki | first2=David G. | last2=Koch | first3=Gibor | last3=Basri | first4=Natalie | last4=Batalhi | first5=Timothy M. | last5=Brown | display-authors=etal | volume=736 | issue=1 | at=19 | date=July 2011 | doi=10.1088/0004-637X/736/1/19 | bibcode=2011ApJ...736...19B | arxiv=1102.0541|s2cid=15233153}}</ref>
<ref name="Szabo2013">{{cite journal | title=Multiple planets or exomoons in Kepler hot Jupiter systems with transit timing variations? | journal=[[Astronomy and Astrophysics]] | first1=R. | last1=Szabó | first2=Gy. M. | last2=Szabó | first3=G. | last3=Dálya | first4=A. E. | last4=Simon | first5=G. | last5=Hodosán | display-authors=etal | volume=553 | at=A17 | date=May 2013 | doi=10.1051/0004-6361/201220132 | bibcode=2013A&A...553A..17S | arxiv=1207.7229|s2cid=118791908}}</ref>
<ref name="Muirhead2012">{{cite journal | title=Characterizing the Cool Kepler Objects of Interests. New Effective Temperatures, Metallicities, Masses, and Radii of Low-mass Kepler Planet-candidate Host Stars | journal=The Astrophysical Journal Letters | first1=Philip S. | last1=Muirhead | first2=Katherine | last2=Hamren | first3=Everett | last3=Schlawin | first4=Bárbara | last4=Rojas-Ayala | first5=Kevin R. | last5=Covey | display-authors=etal | volume=750 | issue=2 | at=L37 | date=May 2012 | doi=10.1088/2041-8205/750/2/L37 | bibcode=2012ApJ...750L..37M | arxiv=1109.1819 | s2cid=27131741}}</ref>
<ref name="Muirhead2013">{{cite journal | title=Characterizing the Cool KOIs. V. KOI-256: A Mutually Eclipsing Post-common Envelope Binary | journal=The Astrophysical Journal | first1=Philip S. | last1=Muirhead | first2=Andrew | last2=Vanderburg | first3=Avi | last3=Shporer | first4=Juliette | last4=Becker | first5=Jonathan J. | last5=Swift | display-authors=etal | volume=767 | issue=2 | at=111 | date=April 2013 | doi=10.1088/0004-637X/767/2/111 | bibcode=2013ApJ...767..111M | arxiv=1304.1165 | s2cid=30368826}}</ref> </references>
{{Stars of Draco|state=collapsed}}
[[Category:Astronomical objects discovered in 2009]] [[Category:Draco (constellation)]] [[Category:Eclipsing binaries]] [[Category:Kepler objects of interest|256]] [[Category:M-type main-sequence stars]] [[Category:White dwarfs]]