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K2-33

Artist's impression of K2-33, with its planet K2-33b transiting across its surface.
Observation data Epoch J2000      Equinox J2000
Constellation	Scorpius
Right ascension	16 10 14.7377
Declination	−19° 19′ 09.408″
Apparent magnitude (V)	14.3
Characteristics
Evolutionary stage	Pre-main-sequence
Spectral type	M2
Astrometry
Proper motion (μ)	RA: −9.592(28) mas/yr Dec.: −23.964(21) mas/yr
Parallax (π)	7.1929 ± 0.0234 mas
Distance	453 ± 1 ly (139.0 ± 0.5 pc)
Details
Mass	0.56 ± 0.09 M☉
Radius	1.05 ± 0.07 R☉
Temperature	3540 ± 70 K
Metallicity	0 dex
Age	9.3 ± 1.2 Myr
Other designations
EPIC 205117205, 2MASS J16101473-1919095, WISE J161014.73-191909.6
Database references
SIMBAD	data

K2-33 is an extremely young pre-main-sequence star located about 453 light-years (139 pc) away from the Earth in the constellation of Scorpius. It is known to host one planet, a super-Neptune, named K2-33b. It is also notable for its young age.

Nomenclature and history

K2-33 also has the 2MASS catalogue number J16101473-1919095 and EPIC designation 205117205.

Planetary candidates were detected around the star by NASA's Kepler Mission on its K2 mission, a mission tasked with discovering planets in transit around their stars. The transit method that Kepler uses involves detecting dips in brightness in stars. These dips in brightness can be interpreted as planets whose orbits pass in front of their stars from the perspective of Earth, although other phenomenon can also be responsible which is why the term planetary candidate is used.

Following the acceptance of the discovery paper, the Kepler team provided an additional moniker for the system of "K2-33". The discoverers referred to the star as K2-33, which is the normal procedure for naming the exoplanets discovered by the spacecraft. Hence, this is the name used by the public to refer to the star and its planet.

Candidate planets that are associated with stars studied by the Kepler Mission are assigned the designations ".01" etc. after the star's name, in the order of discovery. If planet candidates are detected simultaneously, then the ordering follows the order of orbital periods from shortest to longest. Following these rules, there was only one candidate planet were detected, with an orbital period of 5.424865 days.

The designation of b is given to the first planet orbiting a given star, followed by the other letters of the alphabet. In the case of K2-33, there was only one planet, so only the letter b are used. The name K2-33 derives directly from the fact that the star is the catalogued 33rd star discovered by K2 to have confirmed planets.

Stellar characteristics

This star was identified as a young pre-main-sequence object that belongs to the Upper Scorpius subgroup of the Scorpius–Centaurus association in a 2001 article, based on its high lithium content and position in the HR diagram. This is the nearest OB association and recent massive star formation region, with the Upper Scorpius subgroup having a mean distance of 140 parsecs (470 light-years). Direct parallax measurements, by the Gaia spacecraft, indicate that K2-33 is at a distance of 139 ± 0.5 pc, consistent with association to Upper Scorpius. The age of this subgroup is estimated at 11 ± 2 million years, while evolutionary models estimate to K2-33 an independent age of 9.3 million years.

K2-33's spectrum is best modelled with a spectral type of M3.3 and a visual extinction of 0.75 magnitudes, so the star can be considered to be a red dwarf. Its effective temperature has been measured at 3,540 K, which together with the apparent brightness of the star indicates a luminosity of 0.15 times the solar luminosity and a radius of 1.05 times the solar radius. This large size is typical of young stars and indicates that the star is still in the process of contracting towards the main sequence. The mass of this star is not known accurately, and has been estimated at 0.56 or 0.31 times the solar mass. The metallicity of K2-33 is consistent with being equal to the solar value ( = 0).

As a young star, K2-33 has a fast rotation, with a projected rotational velocity of 8.2 km/s. The rotation period of the star, 6.3 days, is known from the light curve obtained by the Kepler spacecraft, causing periodic variations of about 2% in the brightness of the star as star spots appear and disappear from Earth's line of sight. This stellar variability was removed for the analysis of the transit signal of the planet K2-33b.

K2-33 is almost certainly not a binary star. Radial velocity data obtained by the HIRES spectrograph, in the Keck I Telescope, do not show an acceleration larger than 2.6 km/s/yr, which excludes objects more massive than 0.14 solar masses at 3 AU or closer. Adaptive optics infrared observations by the NIRC2 imager, in the Keck II Telescope, can exclude companions more massive than 19 Jupiter masses at 3 AU or further, and 11-12 Jupiter masses at 6-23 AU. The combination of both observational limits only allows for the existence of brown dwarfs or very low mass stars at separations of 1-3 AU.

Planetary system

The only known planet transits the star; this means that the planet's orbit appear to cross in front of their star as viewed from the Earth's perspective. Its inclination relative to Earth's line of sight, or how far above or below the plane of sight it is, vary by less than one degree. This allows direct measurements of the planet's periods and relative diameters (compared to the host star) by monitoring the planet's transit of the star.

K2-33b is known remarkably for its extremely young age, only one other planet is younger (V830 Tau b), with an age of around 2 million years, while K2-33b is only 9.3 million years old. Nonetheless, it is quite a discovery in the search of exoplanets.

Infrared measurements by the Spitzer Space Telescope show that there is still a disk of planetary debris, indicating that planet formation may not be finished yet.

References

1. ^ Vallenari, A.; et al. (Gaia collaboration) (2023). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy and Astrophysics. 674: A1. arXiv:2208.00211. Bibcode:2023A&A...674A...1G. doi:10.1051/0004-6361/202243940. S2CID 244398875. Gaia DR3 record for this source at VizieR.
2. ^ Mann, Andrew W.; et al. (2016). "Zodiacal Exoplanets in Time (ZEIT). III. A Short-Period Planet Orbiting a Pre-Main-Sequence Star in the Upper Scorpius OB Association". The Astronomical Journal. 152 (3) 61: 61. arXiv:1604.06165. Bibcode:2016AJ....152...61M. doi:10.3847/0004-6256/152/3/61.
3. Morton, Timothy; Johnson, John (23 August 2011). "On the Low False Positive Probabilities of Kepler Planet Candidates". The Astrophysical Journal. 738 (2): 170. arXiv:1101.5630. Bibcode:2011ApJ...738..170M. doi:10.1088/0004-637X/738/2/170. S2CID 35223956.
4. NASA (27 January 2014). "Kepler – Discoveries – Summary Table". NASA. Archived from the original on 27 May 2010. Retrieved 1 March 2014.
5. ^ "Kepler Input Catalog search result". Space Telescope Science Institute. Retrieved 18 April 2013.
6. Hessman, F. V.; Dhillon, V. S.; Winget, D. E.; Schreiber, M. R.; Horne, K.; Marsh, T. R.; Guenther, E.; Schwope, A.; Heber, U. (2010). "On the naming convention used for multiple star systems and extrasolar planets". arXiv:1012.0707 .
7. Preibisch, Thomas; Guenther, Eike; Zinnecker, Hans (February 2001). "A Large Spectroscopic Survey for Young Low-Mass Members of the Upper Scorpius OB Association". The Astronomical Journal. 121 (2): 1040–1049. Bibcode:2001AJ....121.1040P. doi:10.1086/318774.
8. Pecaut, Mark J.; Mamajek, Eric E.; Bubar, Eric J. (February 2012). "A Revised Age for Upper Scorpius and the Star Formation History among the F-type Members of the Scorpius–Centaurus OB Association". The Astrophysical Journal. 746 (2) 154: 154. arXiv:1112.1695. Bibcode:2012ApJ...746..154P. doi:10.1088/0004-637X/746/2/154. S2CID 118461108.
9. ^ David, Trevor J.; Hillenbrand, Lynne A.; Petigura, Erik A.; Carpenter, John M.; Crossfield, Ian J. M.; Hinkley, Sasha; Ciardi, David R.; Howard, Andrew W.; Isaacson, Howard T.; Marie Cody, Ann; Schlieder, Joshua E.; Beichman, Charles A.; Barenfeld, Scott A. (2016). "A Neptune-sized transiting planet closely orbiting a 5–10-million-year-old star". Nature. 534 (7609): 658–661. arXiv:1606.06729. Bibcode:2016Natur.534..658D. doi:10.1038/nature18293. PMID 27324846. S2CID 4408972.
10. ^ "NASA's K2 Finds Newborn Exoplanet Around Young Star". Jet Propulsion Laboratory.

v t e Constellation of Scorpius
List of stars in Scorpius Scorpius in Chinese astronomy
Stars	Bayer α (Antares) β (Acrab) δ (Dschubba) ε (Larawag) ζ ζ η θ (Sargas) ι ι κ (Girtab) λ (Shaula) μ (Xamidimura) μ (Pipirima) ν (Jabbah) ξ ο π (Fang) ρ (Iklil) σ (Alniyat) τ (Paikauhale) υ (Lesath) χ ψ ω ω G (Fuyue) H (β Nor) N (α Nor) Q Flamsteed 1 (b) 2 (A) 3 4 11 12 (c) 13 (c) 16 18 22 (i) 25 27 Variable T U RR RS RV RY RZ AH AI AK AR BM CL FQ HK KQ V393 V453 V455 V482 V500 V636 V701 V703 V718 V728 V745 V760 V856 V861 V866 V884 V893 V900 V905 V906 V907 V911 V913 V915 V918 V919 V921 V922 V923 V929 V933 V949 V951 V952 V957 V965 V970 V973 V975 V992 V1003 V1007 V1018 V1026 V1033 V1034 V1036 V1040 V1051 V1058 V1068 V1073 (k) V1074 V1075 V1077 V1094 V1104 V1186 V1187 V1280 V1292 V1294 V1309 HR 5906 5910 5934 5965 5969 5973 5996 5998 5999 6000 6001 6003 6006 6007 6012 6015 6017 6044 6051 6053 6054 6061 6070 (d) 6076 6077 6078 6080 6094 6097 6100 6106 6122 6145 6160 6178 6192 6206 6209 6210 6211 6214 6218 6221 6244 6260 6266 6272 6273 6282 6298 6311 6316 6331 6338 6344 6366 6371 6381 6382 6389 6398 6403 6405 6409 6420 6454 6456 6460 6470 6501 6503 6517 6523 6539 6557 6558 6583 6587 6597 6613 6628 6643 6648 6649 6651 6653 6657 6658 6668 6671 6675 6678 6682 6683 HD 143567 144432 145377 146436 149274 150248 150420 152424 153234 153950 (Rapeto) 155448 155985 158042 159868 162020 Other Gliese 618 Gliese 667 Gliese 682 CD -35 11760 CD -38 10980 EPIC 204278916 EPIC 204376071 GCRT J1745−3009 GSC 06214-00210 GX 340+0 GX 349+2 H1-36 H1743-322 HIP 79431 (Sharjah) IGR J17091-3624 IGR J17252−3616 IRAS 17163−3907 K2-24 K2-33 LSS 4067 MOA-2008-BLG-310L MXB 1735-44 OAO 1657-415 OGLE-2005-BLG-071L OGLE-2005-BLG-390L OGLE-2006-BLG-109L Oph 162225-240515 Pismis 24-1 PSR B1620−26 PSR B1706−44 PSR B1737−30 PSR J1614−2230 Rapid Burster ROXs 12 1RXS J160929.1−210524 1RXS J170849.0−400910 Scorpius X-1 Th 28 Trumpler 27-1 Trumpler 27-27 Trumpler 27-28 Trumpler 27-102 Trumpler 27-105 4U 1700-37 4U 1702-42 4U 1705-44 4U 1724-307 4U 1728-34 4U 1746-371 UScoCTIO 108 VVV-WIT-07 WASP-17 (Dìwö) WR 86 WR 93b Wray 17-96 XTE J1720−318 XTE J1739−302 XTE J1751−305
Exoplanets HD 145377 b HD 153950 b HD 159868 b HIP 78530 b HIP 79431 b K2-24b c K2-33b OGLE-2005-BLG-071Lb OGLE-2005-BLG-390Lb OGLE-2007-BLG-368Lb PSR B1620−26 b (Methuselah) WASP-17b V921 Scorpii b
Star clusters	NGC 6124 6139 6144 6231 6242 6256 6281 6380 6388 6400 6441 6453 6480 6496 Other Messier 4 Messier 7 Messier 80 Trumpler 27
Nebulae	NGC 6072 6153 6302 6334 6337 6357
Galaxies	NGC 6000 Other PKS 1622-297 TXS 1545-234
Category

v t e Exoplanets
Planet Definition IAU Planetary science
Main topics	Exoplanet Exoplanet orbital and physical parameters Methods of detecting exoplanets Planetary system Planet-hosting stars
Sizes and types	Terrestrial Carbon planet Coreless planet Desert planet Dwarf planet Hycean planet Ice planet Iron planet (Super-Mercury) Lava planet Ocean world Mega-Earth Sub-Earth Super-Earth Gaseous Eccentric Jupiter Mini-Neptune (Gas dwarf) Helium planet Hot Jupiter Hot Neptune Gas giant Ice giant Super-Jupiter Super-Neptune Super-puff Ultra-hot Jupiter Ultra-hot Neptune Other types Blanet Brown dwarf Chthonian planet Circumbinary planet Circumtriple planet Disrupted planet Double planet Ecumenopolis Eyeball planet Giant planet Mesoplanet Planemo Planet/Brown dwarf boundary Planetesimal Protoplanet Pulsar planet Sub-brown dwarf Sub-Neptune Toroidal planet Ultra-cool dwarf Ultra-short period planet (USP)
Formation and evolution	Accretion Accretion disk Asteroid belt Circumplanetary disk Circumstellar disc Circumstellar envelope Cosmic dust Debris disk Detached object Disrupted planet Excretion disk Exozodiacal dust Extraterrestrial materials Extraterrestrial sample curation Giant-impact hypothesis Gravitational collapse Hills cloud Internal structure Interplanetary dust cloud Interplanetary medium Interplanetary space Interstellar cloud Interstellar dust Interstellar medium Interstellar space Kuiper belt List of interstellar and circumstellar molecules Merging stars Molecular cloud Nebular hypothesis Oort cloud Outer space Planetary migration Planetary system Planetesimal Planet formation Protoplanetary disk Ring system Rubble pile Sample-return mission Scattered disc Star formation
Systems	Exocomet Interstellar Exomoon Tidally detached Rogue planet Orbits Retrograde Trojan Mean-motion resonances Titius–Bode law
Host stars	A B Binary star Brown dwarfs F/Yellow-white dwarfs G/Yellow dwarfs Herbig Ae/Be K/Orange dwarfs M/Red dwarfs Pulsar Red giant Subdwarf B Subgiant T Tauri White dwarfs Yellow giants
Detection	Astrometry Direct imaging list Microlensing list Polarimetry Timing list Radial velocity list Transit method list Transit-timing variation
Habitability	Astrobiology Astrooceanography Circumstellar habitable zone Earth analog Extraterrestrial liquid water Galactic habitable zone Habitability of binary star systems Habitability of F-type main-sequence star systems Habitability of K-type main-sequence star systems Habitability of natural satellites Habitability of neutron star systems Habitability of red dwarf systems Habitability of yellow dwarf systems Habitable zone for complex life List of potentially habitable exoplanets Tholin Superhabitable planet
Catalogues	Nearby Habitable Systems Exoplanet Data Explorer Extrasolar Planets Encyclopaedia NASA Exoplanet Archive NASA Star and Exoplanet Database Open Exoplanet Catalogue
Lists	Exoplanetary systems Host stars Multiplanetary systems Stars with proto-planetary discs Exoplanets Discoveries Extremes Firsts Nearest Largest Heaviest Terrestrial candidates Kepler 1–500 501–1000 1001–1500 1501–2000 K2 Potentially habitable Proper names Discovered exoplanets by year before 2000 2000–2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022 2023 2024
Other	Carl Sagan Institute Exoplanet naming convention Exoplanet phase curves Exoplanetary Circumstellar Environments and Disk Explorer Extragalactic planet Extrasolar planets in fiction Geodynamics of terrestrial exoplanets Neptunian desert Nexus for Exoplanet System Science Planets in globular clusters Small planet radius gap Sudarsky's gas giant classification
Discoveries of exoplanets Search projects

• Astronomy
• Biology

• 2MASS objects
• Planetary transit variables
• Planetary systems with one confirmed planet
• Pre-main-sequence stars
• Scorpius
• Upper Scorpius