{{Short description|Star in the constellation Draco}} {{Starbox begin}} {{Starbox observe | epoch = J2000 | constell = [[Draco (constellation)|Draco]]<ref name="Roman1987"/> | ra = {{RA|18|59|08.684}}<ref name=GaiaDR3/> | dec = {{DEC|48|25|23.60}}<ref name=GaiaDR3/> | appmag_v = 8.83<ref name=Høg_et_al_2000/> }} {{Starbox character | type = [[Main sequence]] | class = F8V<ref name=Molenda-Żakowicz_et_al_2013/> | b-v = 0.51<ref name=Booth2019/> | variable = }} {{Starbox astrometry | radial_v = −54.76{{±|0.18}}<ref name=Gaia_2022/> | prop_mo_ra = 4.704{{±|0.013}} | prop_mo_dec = 9.263{{±|0.016}} | pm_footnote = <ref name=GaiaDR3/> | parallax = 11.2176 | p_error = 0.0126 | parallax_footnote = <ref name=GaiaDR3/> | absmag_v = }} {{Starbox detail | source = <ref name=Kamiaka2019/> | mass = 1.05{{±|0.04}} | radius = 1.253{{±|0.051}} | gravity = 4.318{{±|0.08|0.089}} | luminosity = 1.864<ref name=Brito_Lopes_2019/> | temperature = 6,080{{±|65}} | metal_fe = −0.138{{±|0.043|0.042}} | rotation = 12.89{{±|0.19}} [[day|d]] | rotational_velocity = 2.8{{±|1.0}} | age_gyr = 7.15{{±|1.61}}<ref name=Booth2019/> }} {{Starbox catalog | names = {{odlist | BD=+48 2806 | GSC=03545-01227 | HD=176693 | Kepler=408 | KOI=1612 | 2MASS=J18590868+4825236 | TYC=3545-1227-1 | KIC=10963065}}, Gaia EDR3 2131593785132997632<ref name=SIMBAD/> }} {{Starbox reference | Simbad = HD+176693 }} {{Starbox end}}
'''HD 176693''', also known as '''Kepler-408''', is a [[star]] with a close orbiting [[exoplanet]] in the northern [[constellation]] of [[Draco (constellation)|Draco]]. It is located at a distance of 291 [[light year]]s from the Sun based on [[stellar parallax|parallax]] measurements, but it is drifting closer with a [[radial velocity]] of −55 km/s.<ref name=Gaia_2022/> The star is predicted to come as close as {{convert|7.0957|pc|ly|1|disp=out|abbr=off}} in 1.6 million years.<ref name=Bailer-Jones_et_al_2018/> It has an [[apparent visual magnitude]] of 8.83,<ref name=Høg_et_al_2000/> which is too faint to be viewed with the naked eye.
The [[stellar spectrum|spectrum]] of HD 176693 matches an [[F-type main-sequence star]] with a [[stellar classification]] of F8V.<ref name=Molenda-Żakowicz_et_al_2013/> The star is older than the Sun, at {{val|7.15|u=billion years}}. It is slightly and uniformly<ref name=Ramírez_et_al_2020/> depleted in heavy elements compared to the Sun, having about 75% of the solar abundance of iron and other heavy elements.<ref name=Kamiaka2019/> HD 176693 is a [[chromosphere|chromospherically]] [[magnetic activity|inactive]] star,<ref name=Booth2019/> although there is weak evidence for [[Tidal acceleration|tidal spin-up]] due to star-planet interaction.<ref name=Metcalfe_Egeland_2019/>
HD 176693 is 5% more massive than the Sun and has a 25% larger radius.<ref name=Kamiaka2019/> It is radiating 1.9<ref name=Brito_Lopes_2019/> times the luminosity of the Sun from its [[photosphere]] at an [[effective temperature]] of 6,080 K. The star is spinning with a [[rotation period]] of 12.89 days.<ref name=Kamiaka2019/> As of 2016, multiplicity surveys have not detect any stellar companions to HD 176693.<ref name=Kraus_et_al_2016/>
==Planetary system== In 2014, a [[Transit (astronomy)|transiting]] [[Sub-Earth]] planet [[Kepler-408b|b]] was detected on a tight 2.5 day orbit. Initially reported with a relatively low confidence of 97.9%,<ref name=Marcy_et_al_2014/> it was confirmed in 2016.<ref name=Campante_et_al_2016/>
The planetary orbit is inclined to the equatorial plane of the star by 41.7{{±|5.1|3.5}}°. Such strong spin-orbit misalignment is unique for a sub-Earth transiting planet, and needs either additional giant planets in the system or a history of close stellar encounters to explain it.<ref name=Kamiaka2019/> The planet may also be a captured body originating from elsewhere.<ref name=Petrovich_et_al_2020/>
{{OrbitboxPlanet begin | name = Kepler-408 | table_ref = <ref name=Kamiaka2019/> }} {{OrbitboxPlanet | exoplanet = [[Kepler-408b|b]] | mass = ≥ 0.02<ref name=Marcy_et_al_2014/> | radius_earth = 0.86{{±|0.04}} | semimajor = | period = 2.465024{{±|0.000005}} | eccentricity = | inclination = 81.85{{±|0.10}} }} {{Orbitbox end}}
==References== {{Reflist|refs=
<ref name=SIMBAD>{{cite simbad | title=Kepler-408 | mode=cs2 | access-date=1 July 2021 }}</ref>
<ref name=GaiaDR3>{{Cite Gaia DR3|2131593785132997632}}</ref>
<ref name=Gaia_2022>{{citation | postscript=. | title=Gaia DR3 Part 1. Main source | author=Gaia Collaboration | date=May 2022 | journal=VizieR Online Data Catalog | doi=10.26093/cds/vizier.1355 | bibcode=2022yCat.1355....0G }}</ref>
<ref name=Booth2019>{{citation | postscript=. | title=Chromospheric emission of solar-type stars with asteroseismic ages | last1=Booth | first1=R. S. | last2=Poppenhaeger | first2=K. | last3=Watson | first3=C. A. | last4=Silva Aguirre | first4=V. | last5=Stello | first5=D. | last6=Bruntt | first6=H. | journal=Monthly Notices of the Royal Astronomical Society | volume=491 | pages=455–467 | year=2020 | issue=1 | doi=10.1093/mnras/stz3039 | doi-access=free | arxiv=1910.12557 | bibcode=2020MNRAS.491..455B | display-authors=1 }}</ref>
<ref name=Brito_Lopes_2019>{{citation | postscript=. | title=The partial ionization zone of heavy elements in F-stars: A study on how it correlates with rotation | last1=Brito | first1=Ana | last2=Lopes | first2=Ilídio | journal=Monthly Notices of the Royal Astronomical Society | volume=488 | issue=2 | pages=1558–1571 | year=2019 | doi=10.1093/mnras/stz1804 | doi-access=free | arxiv=1906.12308 | bibcode=2019MNRAS.488.1558B }}</ref>
<ref name=Ramírez_et_al_2020>{{citation | postscript=. | title=Detailed chemical compositions of planet-hosting stars – I. Exploration of possible planet signatures | last1=Ramírez | first1=I. | last2=Meléndez | first2=J. | last3=Acuña | first3=L. | last4=Spina | first4=L. | last5=Wang | first5=H. S. | last6=Asplund | first6=M. | last7=Yong | first7=D. | last8=Liu | first8=F. | journal=Monthly Notices of the Royal Astronomical Society | volume=495 | issue=4 | pages=3961–3973 | year=2020 | doi=10.1093/mnras/staa1420 | doi-access=free | arxiv=2005.09846 | bibcode=2020MNRAS.495.3961L | display-authors=1 }}</ref>
<ref name=Metcalfe_Egeland_2019>{{citation | postscript=. | title=Understanding the Limitations of Gyrochronology for Old Field Stars | last1=Metcalfe | first1=Travis S. | last2=Egeland | first2=Ricky | journal=The Astrophysical Journal | volume=871 | issue=1 | page=39 | year=2019 | doi=10.3847/1538-4357/aaf575 | arxiv=1811.11905 | bibcode=2019ApJ...871...39M | s2cid=119405127 | doi-access=free }}</ref>
<ref name=Kraus_et_al_2016>{{citation | postscript=. | title=The Impact of Stellar Multiplicity on Planetary Systems. I. The Ruinous Influence of Close Binary Companions | display-authors=1 | last1=Kraus | first1=Adam L. | last2=Ireland | first2=Michael J. | last3=Huber | first3=Daniel | last4=Mann | first4=Andrew W. | last5=Dupuy | first5=Trent J. | journal=The Astronomical Journal | volume=152 | issue=1 | page=8 | year=2016 | doi=10.3847/0004-6256/152/1/8 | arxiv=1604.05744 | bibcode=2016AJ....152....8K | s2cid=119110229 | doi-access=free }}</ref>
<ref name=Marcy_et_al_2014>{{citation | postscript=. | title=Masses, Radii, and Orbits of Small Kepler Planets: The Transition from Gaseous to Rocky Planets | last1=Marcy | first1=Geoffrey W. | last2=Isaacson | first2=Howard | last3=Howard | first3=Andrew W. | last4=Rowe | first4=Jason F. | last5=Jenkins | first5=Jon M. | last6=Bryson | first6=Stephen T. | last7=Latham | first7=David W. | last8=Howell | first8=Steve B. | last9=Gautier | first9=Thomas N. | last10=Batalha | first10=Natalie M. | last11=Rogers | first11=Leslie | last12=Ciardi | first12=David | last13=Fischer | first13=Debra A. | last14=Gilliland | first14=Ronald L. | last15=Kjeldsen | first15=Hans | last16=Christensen-Dalsgaard | first16=Jørgen | last17=Huber | first17=Daniel | last18=Chaplin | first18=William J. | last19=Basu | first19=Sarbani | last20=Buchhave | first20=Lars A. | last21=Quinn | first21=Samuel N. | last22=Borucki | first22=William J. | last23=Koch | first23=David G. | last24=Hunter | first24=Roger | last25=Caldwell | first25=Douglas A. | last26=Van Cleve | first26=Jeffrey | last27=Kolbl | first27=Rea | last28=Weiss | first28=Lauren M. | last29=Petigura | first29=Erik | last30=Seager | first30=Sara | journal=The Astrophysical Journal Supplement Series | volume=210 | issue=2 | page=20 | year=2014 | arxiv=1401.4195 | doi=10.1088/0067-0049/210/2/20 | bibcode=2014ApJS..210...20M | s2cid=10760418 | display-authors=1 }}</ref>
<ref name=Molenda-Żakowicz_et_al_2013>{{citation | postscript=. | title= Atmospheric parameters of 169 F-, G-, K- and M-type stars in the Kepler field | last1=Molenda-Żakowicz | first1=J. | last2=Sousa | first2=S. G. | last3=Frasca | first3=A. | last4=Uytterhoeven | first4=K. | last5=Briquet | first5=M. | last6=Van Winckel | first6=H. | last7=Drobek | first7=D. | last8=Niemczura | first8=E. | last9=Lampens | first9=P. | last10=Lykke | first10=J. | last11=Bloemen | first11=S. | last12=Gameiro | first12=J. F. | last13=Jean | first13=C. | last14=Volpi | first14=D. | last15=Gorlova | first15=N. | last16=Mortier | first16=A. | last17=Tsantaki | first17=M. | last18=Raskin | first18=G. | journal=Monthly Notices of the Royal Astronomical Society | volume=434 | issue=2 | pages=1422 | year=2013 | bibcode= 2013MNRAS.434.1422M | s2cid=59269553 | doi=10.1093/mnras/stt1095 | doi-access= free | arxiv=1306.6011 | display-authors=1 }}</ref>
<ref name=Campante_et_al_2016>{{citation | postscript=. | title=Spin–Orbit Alignment of Exoplanet Systems: Ensemble Analysis Using Asteroseismology | last1=Campante | first1=T. L. | last2=Lund | first2=M. N. | last3=Kuszlewicz | first3=J. S. | last4=Davies | first4=G. R. | last5=Chaplin | first5=W. J. | last6=Albrecht | first6=S. | last7=Winn | first7=J. N. | last8=Bedding | first8=T. R. | last9=Benomar | first9=O. | last10=Bossini | first10=D. | last11=Handberg | first11=R. | last12=Santos | first12=A. R. G. | last13=Van Eylen | first13=V. | last14=Basu | first14=S. | last15=Christensen-Dalsgaard | first15=J. | last16=Elsworth | first16=Y. P. | last17=Hekker | first17=S. | last18=Hirano | first18=T. | last19=Huber | first19=D. | last20=Karoff | first20=C. | last21=Kjeldsen | first21=H. | last22=Lundkvist | first22=M. S. | last23=North | first23=T. S. H. | last24=Silva Aguirre | first24=V. | last25=Stello | first25=D. | last26=White | first26=T. R. | display-authors=1 | journal=The Astrophysical Journal | volume=819 | issue=1 | page=85 | year=2016 | doi=10.3847/0004-637X/819/1/85 | arxiv=1601.06052 | bibcode=2016ApJ...819...85C | s2cid=56307453 | doi-access=free }}</ref>
<ref name=Kamiaka2019>{{citation | postscript=. | title=The Misaligned Orbit of the Earth-sized Planet Kepler-408b | last1=Kamiaka | first1=Shoya | last2=Benomar | first2=Othman | last3=Suto | first3=Yasushi | last4=Dai | first4=Fei | last5=Masuda | first5=Kento | last6=Winn | first6=Joshua N. | display-authors=1 | journal=The Astronomical Journal | volume=157 | issue=4 | page=137 | year=2019 | doi=10.3847/1538-3881/ab04a9 | doi-access=free | arxiv=1902.02057 | bibcode=2019AJ....157..137K | s2cid=118909208 }}</ref>
<ref name=Petrovich_et_al_2020>{{citation | postscript=. | title=A Disk-driven Resonance as the Origin of High Inclinations of Close-in Planets | last1=Petrovich | first1=Cristobal | last2=Muñoz | first2=Diego J. | last3=Kratter | first3=Kaitlin M. | last4=Malhotra | first4=Renu | display-authors=1 | journal=The Astrophysical Journal Letters | volume=902 | issue=1 | pages=L5 | year=2020 | arxiv=2008.08587 | bibcode=2020ApJ...902L...5P | s2cid=221186597 | doi=10.3847/2041-8213/abb952 | doi-access=free }}</ref>
<ref name=Bailer-Jones_et_al_2018>{{citation | postscript=. | title=New stellar encounters discovered in the second Gaia data release | last1=Bailer-Jones | first1=C.A.L. | last2=Rybizki | first2=J | last3=Andrae | first3=R. | last4=Fouesnea | first4=M. | display-authors=1 | journal=Astronomy & Astrophysics | volume=616 | pages=A37 | date=2018 | bibcode=2018A&A...616A..37B | doi=10.1051/0004-6361/201833456 | arxiv=1805.07581 | s2cid=56269929 }}</ref>
<ref name=Høg_et_al_2000>{{citation | postscript=. | title=The Tycho-2 catalogue of the 2.5 million brightest stars | journal=Astronomy and Astrophysics | last1=Høg | first1=E. | last2=Fabricius | first2=C. | last3=Makarov | first3=V. V. | last4=Urban | first4=S. | last5=Corbin | first5=T. | last6=Wycoff | first6=G. | last7=Bastian | first7=U. | last8=Schwekendiek | first8=P. | last9=Wicenec | first9=A. | display-authors=1 | volume=355 | pages=L27–L30 | date=March 2000 | bibcode=2000A&A...355L..27H | doi=10.1888/0333750888/2862 }}</ref>
<ref name="Roman1987">{{Cite constellation|Kepler-408}}</ref>
}}
{{Draco (constellation)}} {{Sky|18|59|08.6847|+|48|25|23.5990}} {{Portal bar|Astronomy|Stars|Outer space}}
{{DEFAULTSORT:HD 176693}} <!-- Properties --> [[Category:F-type main-sequence stars]] [[Category:Planetary systems with one confirmed planet]] [[Category:Planetary transit variables]] <!-- Location/catalogues --> [[Category:Draco (constellation)]] [[Category:Durchmusterung objects|BD+48 2806]] [[Category:Kepler objects of interest|1612]] [[Category:Henry Draper Catalogue objects|176693]]