{{Short description|Star in the constellation Taurus}} {{Starbox begin}} {{starbox image | image = 250px | caption = Atacama Large Millimeter Array image of CI Tauri, showing three gaps in the disk }} {{Starbox observe | epoch = J2000 | constell = Taurus | ra = {{RA|04|33|52.01440}}<ref name="GaiaDR3"/> | dec = {{DEC|+22|50|30.0941}}<ref name="GaiaDR3"/> | appmag_v = 13.8<ref name="SIMBAD" /> }} {{Starbox character | type = T Tauri star | class = K4IVe<ref name="SIMBAD" /> | b-v = | u-b = | variable = Orion variable }} {{Starbox astrometry | radial_v = {{nowrap|+16.2}}<ref name="SIMBAD"/> | prop_mo_ra = +8.942 | prop_mo_dec = –17.079 | pm_footnote = <ref name="GaiaDR3"/> | parallax = 6.2376 | p_error = 0.0205 | parallax_footnote = <ref name="GaiaDR3"/> | absmag_v = }} {{Starbox detail | mass = {{val|0.90|0.02}}<ref name="Flagg2019"/> | radius = 1.679<ref name="NASAExoplanetArchive" /> | gravity = | metal_fe = | temperature = | luminosity = | rotational_velocity = | rotation = 6.6 d<ref name="Biddle2021"/> or 9 d<ref name="Manick2024"/> | age_myr = 2-3<ref name="Flagg2019"/> }} {{Starbox catalog | names = CI Tau, 2MASS J04335200+2250301, EPIC 247584113<ref name="SIMBAD"/> }} {{Starbox reference |Simbad = CI+Tauri }} {{Starbox end}}
'''CI Tauri''' is a young star, about 2 million years old, located approximately {{convert|523|ly|pc|lk=on|abbr=off}} away in the constellation Taurus. It is still accreting material from a debris disk at an unsteady pace, possibly modulated by the eccentric<ref name="Teyssandier2020"/> orbital motion of an inner planet.<ref name="Biddle2018"/> The spectral signatures of compounds of sulfur were detected from the disk.<ref name=Gal2019/>
The magnetic field on the surface of CI Tauri, equal to 0.22 T, is close to average for T Tauri stars.<ref name="Sokal2020"/>
==Planetary system== [[File:CITauLightCurve.png|thumb|left|A broad-band optical light curve for CI Tauri, adapted from Roggero ''et al.'' (2021)<ref name="Roggero"/>]] CI Tauri hosts a protoplanetary disk, and evidence for planets has been found via both radial velocity and disk morphology.<ref name="Clarke"/><ref name="Manick2024"/>
===Radial velocity=== CI Tauri displays several periodic radial velocity variations, including periods of 6.6 days, 9 days, and 25 days.<ref name="Manick2024"/> The 9-day period was proposed to be due to a candidate massive planet on an eccentric orbit, CI Tauri b, in 2016.<ref name="Johns-Krull2016"/> The discovery of CI Tauri b was notable because it is a hot Jupiter, which are supposed to take a minimum of 10 million years to form, and are often thought to be too close to their parent stars to have formed there.<ref name="Astronomy Now"/><ref name="Cambridge"/>
The existence of this planet has been debated; in 2019, a detection of carbon monoxide attributed to the planet's atmosphere was announced, seemingly confirming it.<ref name="Flagg2019"/> However, a 2020 study found that the star rotates with a period of 9 days, and suggested that the radial velocity variations may be caused by the star's rotation rather than a planet. The carbon monoxide detection was attributed to magnetic interaction of the star with the circumstellar disk.<ref name="Donati2020"/> Other studies have attributed the 6.6-day period to the stellar rotation and the 9-day period to the candidate planet.<ref name="Biddle2018"/><ref name="Biddle2021"/>
A 2024 study found evidence for a planetary origin of the 25-day radial velocity signal, while considering the 9-day signal to correspond to the stellar rotation and be caused by a starspot.<ref name="Manick2024"/> This 25-day candidate planet would orbit CI Tauri at a distance of {{val|0.17|u=AU}} in a highly-eccentric orbit {{Nowrap|1=(e = 0.58)}}. The mass of this planet is estimated to be {{val|3.6|0.3|ul=Jupiter mass}}.<ref name="Manick2024"/> While this is treated as a strong candidate and left undesignated by its discovery paper, the NASA Exoplanet Archive lists it as a confirmed planet with the designation CI Tauri c.<ref name="NASAExoplanetArchive"/> Another study in 2025 using additional observations detected the 25-day period only in the CO spectral lines, but not in atomic lines, which suggests that this periodicity is instead caused by a structure in the disk, or by a lower-mass planet orbiting at a distance of 0.16 astronomical units. The latter scenario is supported by other observations.<ref name=Donati2024/>
===Disk morphology=== In 2018 the possible detection of three more planets, inferred by gaps in the protoplanetary disk surrounding the star, was announced. Using the Atacama Large Millimeter Array (ALMA) to look for 'siblings' of CI Tauri b, a team of researchers detected three distinct gaps in the protoplanetary disk which their theoretical modelling suggests are caused by three other planets. The two outer planets are believed to be about the mass of Saturn, while the inner planet's mass is around the same as Jupiter.<ref name="Cambridge" /> Two of the new planets are similarly located to those inferred in the HL Tauri protoplanetary disk.<ref name="Clarke"/>
Another 2018 study also found evidence for the outermost of these planets at around 100 AU, estimating a mass of 0.25-0.8 times that of Jupiter.<ref name="Konishi2018"/> If this discovery is confirmed this would be the most massive collection of exoplanets ever detected at this age with its four planets spanning a factor of a thousand in orbital radius.<ref name="Clarke" />
The gaps are visible in wideband photography, but not in the gas spectral lines. These "gaps" may be lower-temperature shadows of dust in the inner disk cast on outer parts rather than true gaps carved by planets.<ref name="Rosotti2021"/>
{{OrbitboxPlanet begin | name = CI Tauri | table_ref = <ref name="Flagg2019"/><ref name="Manick2024"/><ref name="Clarke"/>{{rp|5}} }} {{OrbitboxPlanet hypothetical | exoplanet = b | mass = {{val|11.6|2.9|2.7}} | radius = | semimajor = | period = {{val|8.9891|0.0202}} | eccentricity = {{val|0.25|0.16}} | inclination = {{val|50.5|6.3|8.5}} | status = false positive<ref name="NASAExoplanetArchive" /> }} {{OrbitboxPlanet hypothetical | status = disputed<ref name=Donati2024/> | exoplanet = c <!-- Manick2024 candidate, undesignated in source --> | mass = {{val|3.6|0.3}} | radius = | semimajor = {{val|0.17|0.08}} | period = {{val|25.2|1.7|1.8}} | eccentricity = {{val|0.58|0.05|0.06}} | inclination = }} {{OrbitboxPlanet hypothetical | exoplanet = <!-- Clarke2018 candidate, undesignated in source --> | mass = ~0.75 | radius = | semimajor = ~14 | period = | eccentricity = | inclination = }} {{OrbitboxPlanet hypothetical | exoplanet = <!-- Clarke2018 candidate, undesignated in source --> | mass = ~0.15 | radius = | semimajor = ~43 | period = | eccentricity = | inclination = }} {{OrbitboxPlanet hypothetical | exoplanet = <!-- Clarke2018 candidate, undesignated in source --> | mass = ~0.4 | radius = | semimajor = ~108 | period = | eccentricity = | inclination = }} {{OrbitboxPlanet disk | disk = debris disk<ref name=Gal2019/> | periapsis = 200 | apoapsis = 600 | inclination = 50.3 }} {{Orbitbox end}}
==References== {{Reflist|refs=
<ref name="SIMBAD">{{cite web |title=V* CI Tau -- T Tau-type Star |url=http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=ci+tau&submit=SIMBAD+search |website=SIMBAD |access-date=19 October 2018}}</ref>
<ref name="GaiaDR3">{{Cite Gaia DR3|145203159127518336}}</ref>
<ref name="NASAExoplanetArchive">{{cite web |url=https://exoplanetarchive.ipac.caltech.edu/overview/CI%20Tau |title=CI Tau |website=NASA Exoplanet Archive |access-date=29 March 2024}}</ref>
<ref name="Johns-Krull2016">{{cite journal|arxiv=1605.07917|year=2016|title=A Candidate Young Massive Planet in Orbit around the Classical T Tauri Star CI Tau|doi=10.3847/0004-637X/826/2/206|last1=Johns-Krull|first1=Christopher M.|last2=McLane|first2=Jacob N.|last3=Prato|first3=L.|last4=Crockett|first4=Christopher J.|last5=Jaffe|first5=Daniel T.|last6=Hartigan|first6=Patrick M.|last7=Beichman|first7=Charles A.|last8=Mahmud|first8=Naved I.|last9=Chen|first9=Wei|last10=Skiff|first10=B. A.|last11=Wilson Cauley|first11=P.|last12=Jones|first12=Joshua A.|last13=Mace|first13=G. N.|journal=The Astrophysical Journal|volume=826|issue=2|page=206|bibcode=2016ApJ...826..206J|s2cid=19060087 |doi-access=free }}</ref>
<ref name="Astronomy Now">{{cite web |title=Astronomers find giant planet around very young star CI Tauri |url=https://astronomynow.com/2016/05/27/astronomers-find-giant-planet-around-very-young-star-ci-tauri/ |website=Astronomy Now |access-date=20 October 2018}}</ref>
<ref name="Cambridge">{{cite web |title=Giant planets around young star raise questions about how planets form |url=https://www.cam.ac.uk/research/news/giant-planets-around-young-star-raise-questions-about-how-planets-form |website=University of Cambridge |access-date=20 October 2018|date=2018-10-15 }}</ref>
<ref name="Biddle2018">{{cite journal|arxiv=1801.06234|title=K2 reveals pulsed accretion driven by the 2 Myr old hot Jupiter CI Tau b|year=2018|doi=10.3847/2041-8213/aaa897|last1=Biddle|first1=Lauren I.|last2=Johns-Krull|first2=Christopher M.|last3=Llama|first3=Joe|last4=Prato |first4=Lisa A. |last5=Skiff|first5=Brian A.|journal=The Astrophysical Journal|volume=853|issue=2|pages=L34|bibcode=2018ApJ...853L..34B|s2cid=111379078 |doi-access=free }}</ref>
<ref name="Konishi2018">{{cite journal|arxiv=1805.07498|title=Probing Signatures of a Distant Planet around the Young T-Tauri Star CI Tau Hosting a Possible Hot Jupiter|year=2018|doi=10.3847/2041-8213/aac6d2|last1=Konishi|first1=Mihoko|last2=Hashimoto|first2=Jun|last3=Hori|first3=Yasunori|journal=The Astrophysical Journal|volume=859|issue=2|pages=L28|bibcode=2018ApJ...859L..28K|s2cid=119208569 |doi-access=free }}</ref>
<ref name=Donati2024>{{Cite journal |last1=Donati |first1=J -F |last2=Finociety |first2=B |last3=Cristofari |first3=P I |last4=Alencar |first4=S H P |last5=Moutou |first5=C |last6=Delfosse |first6=X |last7=Fouqué |first7=P |last8=Arnold |first8=L |last9=Baruteau |first9=C |last10=Kóspál |first10=á |last11=Ménard |first11=F |last12=Carmona |first12=A |last13=Grankin |first13=K |last14=Takami |first14=M |last15=Artigau |first15=E |date=2024-04-05 |title=The classical T Tauri star CI Tau observed with SPIRou: magnetospheric accretion and planetary formation |journal=Monthly Notices of the Royal Astronomical Society |language=en |volume=530 |issue=1 |pages=264–286 |doi=10.1093/mnras/stae675 |doi-access=free |issn=0035-8711}}</ref>
<ref name="Clarke">{{Cite journal |last1=Clarke |first1=Cathie J |last2=Tazzari |first2=Marco |last3=Juhasz |first3=Attila |last4=Rosotti |first4=Giovanni |last5=Booth |first5=Richard |last6=Facchini |first6=Stefano |last7=Ilee |first7=John D |last8=Johns-Krull |first8=Christopher M |last9=Kama |first9=Mihkel |last10=Meru |first10=Farzana |last11=Prato |first11=Lisa A. |title=High resolution millimetre imaging of the CI Tau protoplanetary disc - a massive ensemble of protoplanets from 0.1 - 100 au |journal=The Astrophysical Journal |volume=866 |pages=L6 |doi=10.3847/2041-8213/aae36b|arxiv=1809.08147 |year=2018 |issue=1 |s2cid=119042020 |doi-access=free |bibcode=2018ApJ...866L...6C}}</ref>
<ref name=Gal2019>{{cite journal|arxiv=1903.11105|title=Sulfur chemistry in protoplanetary disks: CS and H2CS|year=2019|doi=10.3847/1538-4357/ab1416|last1=Le Gal|first1=Romane|last2=Öberg|first2=Karin I.|last3=Loomis|first3=Ryan A.|last4=Pegues|first4=Jamila|last5=Bergner|first5=Jennifer B.|journal=The Astrophysical Journal|volume=876|issue=1|page=72|bibcode=2019ApJ...876...72L|s2cid=85528537 |doi-access=free }}</ref>
<ref name="Flagg2019">{{cite journal|arxiv=1906.02860|title=CO Detected in CI Tau b: Hot Start Implied by Planet Mass and MK|year=2019|doi=10.3847/2041-8213/ab276d|last1=Flagg|first1=Laura|last2=Johns-Krull|first2=Christopher M.|last3=Nofi|first3=Larissa|last4=Llama|first4=Joe|last5=Prato |first5=Lisa A. |last6=Sullivan|first6=Kendall|last7=Jaffe|first7=D. T.|last8=Mace|first8=Gregory|journal=The Astrophysical Journal|volume=878|issue=2|pages=L37|bibcode=2019ApJ...878L..37F|s2cid=174801528 |doi-access=free }}</ref>
<ref name="Sokal2020">{{cite journal|arxiv=1911.00784|title=The Mean Magnetic Field Strength of CI Tau|year=2020|doi=10.3847/1538-4357/ab59d8|last1=Sokal|first1=Kimberly R.|last2=Johns-Krull|first2=Christopher M.|last3=Mace|first3=Gregory N.|last4=Nofi|first4=Larissa|last5=Prato |first5=Lisa A. |last6=Lee|first6=Jae-Joon|last7=Jaffe|first7=Daniel T.|journal=The Astrophysical Journal|volume=888|issue=2|page=116|bibcode=2020ApJ...888..116S|s2cid=207870483 |doi-access=free }}</ref>
<ref name="Teyssandier2020">{{cite journal|arxiv=1911.08492|title=Pulsed Disc Accretion Driven by Hot Jupiters|year=2020|doi=10.1093/mnras/staa1363|last1=Lai|first1=Dong|last2=Teyssandier|first2=Jean|journal=Monthly Notices of the Royal Astronomical Society|volume=495|issue=4|pages=3920–3928|doi-access=free |bibcode=2020MNRAS.495.3920T|s2cid=208175992}}</ref>
<ref name="Donati2020">{{cite journal |last1=Donati |first1=J.-F. |last2=Bouvier |first2=J. |display-authors=etal |date=February 2020 |title=The magnetic field and accretion regime of CI Tau |journal=Monthly Notices of the Royal Astronomical Society |volume=491 |issue=4 |pages=5660–5670 |doi=10.1093/mnras/stz3368 |doi-access=free |arxiv=1911.12818 |bibcode=2020MNRAS.491.5660D}}</ref>
<ref name="Biddle2021">{{cite journal |last1=Biddle |first1=Lauren I. |last2=Llama |first2=Joe |display-authors=etal |date=January 2021 |title=Amplitude Modulation of Short-timescale Hot Spot Variability |journal=The Astrophysical Journal |volume=906 |issue=2 |pages=113 |doi=10.3847/1538-4357/abc889 |doi-access=free |arxiv=2011.05388 |bibcode=2021ApJ...906..113B}}</ref>
<ref name="Rosotti2021">{{cite journal|arxiv=2012.07848|title=High resolution observations of molecular emission lines toward the CI Tau proto-planetary disc: planet-carved gaps or shadowing?|year=2020|doi=10.1093/mnras/staa3869|last1=Rosotti|first1=Giovanni P.|last2=Ilee|first2=John D.|last3=Facchini|first3=Stefano|last4=Tazzari|first4=Marco|last5=Booth|first5=Richard A.|last6=Clarke|first6=Cathie|last7=Kama|first7=Mihkel|journal=Monthly Notices of the Royal Astronomical Society|volume=501 |issue=3 |page=3427 |doi-access=free |bibcode=2021MNRAS.501.3427R|s2cid=229180958}}</ref>
<ref name="Roggero">{{cite journal |last1=Roggero |first1=Noemi |last2=Bouvier |first2=Jérôme |last3=Rebull |first3=Luisa M. |last4=Cody |first4=Ann Marie |title=The dipper population of Taurus seen with K2 |journal=Astronomy and Astrophysics |date=July 2021 |volume=651 |pages=A44 |doi=10.1051/0004-6361/202140646 |arxiv=2106.02064 |bibcode=2021A&A...651A..44R |s2cid=235352553 }}</ref>
<ref name="Manick2024">{{Citation |last1=Manick |first1=R. |last2=Sousa |first2=A. P. |last3=Bouvier |first3=J. |last4=Almenara |first4=J. M. |last5=Rebull |first5=L. |last6=Bayo |first6=A. |last7=Carmona |first7=A. |last8=Martioli |first8=E. |last9=Venuti |first9=L. |display-authors=2 |date=March 2024 |title=Long period modulation of the classical T Tauri star CI Tau: evidence for an eccentric close-in massive planet at 0.17 au |journal=Astronomy & Astrophysics |volume=686 |doi=10.1051/0004-6361/202348258 |arxiv=2403.03706|bibcode=2024A&A...686A.249M }}</ref>
}}
{{Stars of Taurus}}
Category:Taurus (constellation) Category:T Tauri stars Category:Planetary systems with one confirmed planet Tauri, CI Category:Circumstellar disks