V1298 Tauri
Star in the constellation Taurus
V1298 Tauri

The planetary system V1298 Tauri
Credit: Exoplanet Exploration Program and the Jet Propulsion Laboratory for NASA’s Astrophysics Division
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Taurus
Right ascension 04h 05m 19.59121s[1]
Declination +20° 09′ 25.5635″[1]
Apparent magnitude (V) 10.31 - 10.43[2]
Characteristics
Evolutionary stage pre-main sequence[3]
Spectral type K0-K1.5[3]
Variable type Irregular[2]
Astrometry
Proper motion (μ) RA: +5.228±0.131[1] mas/yr
Dec.: −16.077±0.048[1] mas/yr
Parallax (π)9.2139±0.0593 mas[1]
Distance354 ± 2 ly
(108.5 ± 0.7 pc)
Details
Mass1.095+0.049
−0.047[4] M☉
Radius1.33+0.04
−0.03[4] R☉
Luminosity0.934±0.044[3] L☉
Surface gravity (log g)4.43[5] cgs
Temperature4,970±120[3] K
Rotation2.97+0.03
−0.04 d[4]
Rotational velocity (v sin i)26.6[5] km/s
Age23±4[3] Myr
Other designations
K2-309, 2MASS J04051959+2009256, BD+19 656, EPIC 210818897, RX J0405.3+2009, 1SWASP J040519.59+200925.5
Database references
SIMBADdata

V1298 Tauri is a young (23±4 Myr) weakly-lined T Tauri star[6] that is part of the Taurus-Auriga association in the Taurus Molecular Cloud. Alternatively it is part of a proposed moving group, called Group 29 (or 93 Tau group) that is slightly older.[7][8][3][9] The system has four transiting exoplanets, discovered with the Kepler space telescope in the K2 mission.[6] One of the planets was discovered in August 2019[3] and the other three were discovered in November 2019 by the same team.[6]

Stellar characteristics

A light curve for V1298 Tauri, adapted from David et al. (2019)[3]

V1298 Tauri has a spectral type of K0 - K1.5 and it has a mass of about 1.1 M☉. The star appears in x-rays from ROSAT data and it does show strong lithium absorption lines, both signatures of youth and therefore it was a proposed member of Taurus-Auriga. On the other hand it does not show signs of accretion and it lacks infrared excess. Instead it shows H-alpha in absorption.[3]

In 2007, Konstantin Nikolaevich Grankin et al. announced their discovery that V1298 Tauri is a variable star.[10] It was given its variable star designation in 2011.[11] The brightness of V1298 Tauri varies in an unpredictable way between a maximum visual magnitude of 10.31 and a minimum of 10.54.[2] The light curve of the star shows quasi-periodic variability that was interpreted as stellar rotation and starspots. The light curve also showed several flares.[3]

Based on Gaia DR2 data this star is part of a co-moving pair, together with HD 284154.[7] The star is included in an analysis of the 93 Tau group, which finds an age of 35±5 Myrs.[9]

Planetary system

The planets around V1298 Tauri are among the lowest exoplanet densities ever recorded, which is attributed to their young age. Over time the planets will shrink and become super-Eaths and sub-Neptunes. Additionally planet c is suspected to have a ‘boil-off’ phase when the disk around the star disperses.[12]

V1298 Tauri has four confirmed planets of which planets c, d and b are near a 1:2:3 resonance (with periods of 8.25, 12.40 and 24.14 days). Planet e only shows a single transit in the K2 light curve and has a period larger than 36 days. Planet e might be in a low-order resonance (of 2:3, 3:5, 1:2, or 1:3) with planet b. The system is very young and might be a precursor of a compact multiplanet system. The 2:3 resonance suggests that some close-in planets may either form in resonances or evolve into them on timescales of less than 10 Myr. The planets in the system have a size between Neptune and Saturn. Only planet b has a size similar to Jupiter.[6]

Models predict that the planets have a minimum core mass of 5 M🜨 and are surrounded by a thick envelope that make up 20% of their mass. The total mass of planet c and d was predicted to be 2 - 28 M🜨 and the total mass of planet d and b was predicted to be 9 - 120 M🜨.[6] In a follow-up paper the mass of V1298 Tauri b was constrained to <2.2 MJ.[13] The planet c was suspected to be shedding mass due to intense irradiation by the host star, but hydrogen tail existence was refuted by 2021.[14] Additionally planet c has a non-detection of helium, which provided limits for mass-loss rates.[15]

Orbits of the planets b and c are nearly coplanar and planet c is not inclined to the equatorial plane of the star, misalignment equals to 2+12
−4 degrees.[16]

Planet b was observed with Hubble WFC3 and a transmission spectrum was produced. This observation found a clear primordial atmosphere and water vapor absorption. The mass was constrained from this observation to less than 23 earth-masses, making this planet one of the lowest density planet observed. The team retrieved a low metallicity for the atmosphere, challenging formation mechanisms. The planet will likely evolve into a sub-Neptune in the future.[17] Comparison between the transmission spectrum of planet b and a newly obtained WFC3 transmission spectrum for planet c found that planet b has a large, haze-free envelope. For planet c hazes could not be ruled out. The masses were constrained for planet b to below 20 earth masses and for planet c to 17+13
−6 earth masses. An ongoing transit-timing variation study suggest that both planet b and c are in the mass range of super-Earth to sub-Neptune planets and will evolve into these types of planet.[18] A team studied planet b with JWST NIRSpec transmission spectroscopy with a combination of Hubble observations. The team found a haze-free, H/He-dominated atmosphere with a large scale height of around 1500 km. The team detected carbon dioxide, water vapor, methane, sulfur dioxide and carbonyl sulfide in the atmosphere of the planet. The mass was inferred to be 12 ± 1 M🜨 (free retrieval) and 12 ± 1 M🜨 (grid modelling) using the scale height. The metallicity was found to be low compared to a mature sub-Neptune. Especially methane was found to be lower than equilibrium chemistry. The model requires the planet to have a hot internal temperature of 500 K (227 °C; 440 °F) and vertical mixing, which helps to explain the low methane. This hot internal temperature is higher than expected. The planet might have a deep atmospheric metallicity gradient and mass loss from the atmosphere might enhance the metallicity over time.[19]

Planet e could be a planet with a water-rich core and an substantial hydrogen envelope.[20] Planet e was possibly detected by Kepler, TESS and CHEOPS in three transits with an orbital period of around 45 days. The transits have different depths, lengths and maybe has TTVs of a few hours. Alternatively CHEOPS could have detected a fifth planet.[21]

The V 1298 Tauri planetary system[12]
Companion
(in order from star) 		Mass Semimajor axis
(AU) 		Orbital period
(days) 		Eccentricity Inclination Radius
c 4.7±0.6 M🜨 0.0824±0.0012 8.249164(3) <0.0094 88.49+0.92
−0.72[6]° 		5.08±0.37 R🜨
d 6.0±0.7 M🜨 0.1081±0.0016 12.401394(9) <0.0087 89.04+0.65
−0.73[6]° 		6.53±0.42 R🜨
b 13.1±5.3 M🜨 0.1685±0.0025 24.140006(17) 0.0079±0.0041 89.00+0.46
−0.24[6]° 		9.41±0.57 R🜨
e 15.3±4.2 MJ 0.2689±0.0040 48.677714(53) <0.0124 89.40+0.26
−0.18[6]° 		10.17±0.75 R🜨

See also

References

  1. ^ a b c d e Gaia Collaboration (2018-08-01). "Gaia Data Release 2 - Summary of the contents and survey properties". Astronomy & Astrophysics. 616: A1. arXiv:1804.09365. Bibcode:2018A&A...616A...1G. doi:10.1051/0004-6361/201833051. ISSN 0004-6361. S2CID 49211658.
  2. ^ a b c Samus, N. N.; Durlevich, O. V.; et al. (2009). "VizieR Online Data Catalog: General Catalogue of Variable Stars (Samus+ 2007-2013)". VizieR On-line Data Catalog: B/GCVS. Originally Published in: 2009yCat....102025S. 1: B/GCVS. Bibcode:2009yCat....102025S.
  3. ^ a b c d e f g h i j David, Trevor J.; Cody, Ann Marie; Hedges, Christina L.; Mamajek, Eric E.; Hillenbrand, Lynne A.; Ciardi, David R.; Beichman, Charles A.; Petigura, Erik A.; Fulton, Benjamin J.; Isaacson, Howard T.; Howard, Andrew W. (August 2019). "A Warm Jupiter-sized Planet Transiting the Pre-main-sequence Star V1298 Tau". The Astronomical Journal. 158 (2): 79. arXiv:1902.09670. Bibcode:2019AJ....158...79D. doi:10.3847/1538-3881/ab290f. ISSN 0004-6256. S2CID 119003936.
  4. ^ a b c Feinstein, Adina D.; David, Trevor J.; Montet, Benjamin T.; Foreman-Mackey, Daniel; Livingston, John H.; Mann, Andrew W. (2022). "V1298 Tau with TESS: Updated Ephemerides, Radii, and Period Constraints from a Second Transit of V1298 Tau E". The Astrophysical Journal Letters. 925 (1): L2. arXiv:2111.08660. Bibcode:2022ApJ...925L...2F. doi:10.3847/2041-8213/ac4745. S2CID 244130016.
  5. ^ a b Abdurro'uf; et al. (2022). "The Seventeenth Data Release of the Sloan Digital Sky Surveys: Complete Release of MaNGA, MaStar, and APOGEE-2 Data". The Astrophysical Journal Supplement Series. 259 (2): 35. arXiv:2112.02026. Bibcode:2022ApJS..259...35A. doi:10.3847/1538-4365/ac4414.
  6. ^ a b c d e f g h i David, Trevor J.; Petigura, Erik A.; Luger, Rodrigo; Foreman-Mackey, Daniel; Livingston, John H.; Mamajek, Eric E.; Hillenbrand, Lynne A. (2019-10-29). "Four Newborn Planets Transiting the Young Solar Analog V1298 Tau". The Astrophysical Journal. 885 (1): L12. arXiv:1910.04563. Bibcode:2019ApJ...885L..12D. doi:10.3847/2041-8213/ab4c99. ISSN 2041-8213. S2CID 204008446.
  7. ^ a b Oh, Semyeong; Price-Whelan, Adrian M.; Hogg, David W.; Morton, Timothy D.; Spergel, David N. (June 2017). "Comoving Stars in Gaia DR1: An Abundance of Very Wide Separation Comoving Pairs". The Astronomical Journal. 153 (6): 257. arXiv:1612.02440. Bibcode:2017AJ....153..257O. doi:10.3847/1538-3881/aa6ffd. ISSN 0004-6256. S2CID 119351439.
  8. ^ Luhman, K. L. (December 2018). "The Stellar Membership of the Taurus Star-forming Region". The Astronomical Journal. 156 (6): 271. arXiv:1811.01359. Bibcode:2018AJ....156..271L. doi:10.3847/1538-3881/aae831. ISSN 0004-6256. S2CID 119471553.
  9. ^ a b Luhman, K. L. (2023-02-01). "A Census of the Taurus Star-forming Region and Neighboring Associations with Gaia". The Astronomical Journal. 165 (2): 37. arXiv:2211.09785. Bibcode:2023AJ....165...37L. doi:10.3847/1538-3881/ac9da3. ISSN 0004-6256.
  10. ^ Grankin, K. N.; Artemenko, S. A.; Melnikov, S. Y. (January 2007). "Photometry of 39 PMS Variables in the Taurus-Auriga Region" (PDF). Information Bulletin on Variable Stars. 5752: 1–4. Bibcode:2007IBVS.5752....1G. Retrieved 31 August 2025.
  11. ^ Kazarovets, E. V.; Samus, N. N.; Durlevich, O. V.; Kireeva, N. N. (January 2011). "The 80th Name-List of Variable Stars. Part I - RA 0h to 6h" (PDF). Information Bulletin on Variable Stars. 5969: 1–21. Bibcode:2011IBVS.5969....1K. Retrieved 31 August 2025.
  12. ^ a b Livingston, John H.; Petigura, Erik A.; David, Trevor J.; Masuda, Kento; Owen, James; Nesvorný, David; Batygin, Konstantin; de Leon, Jerome; Mori, Mayuko; Ikuta, Kai; Fukui, Akihiko; Watanabe, Noriharu; Orell Miquel, Jaume; Murgas, Felipe; Parviainen, Hannu (January 2026). "A young progenitor for the most common planetary systems in the Galaxy". Nature. 649 (8096): 310–314. doi:10.1038/s41586-025-09840-z. ISSN 1476-4687. PMID 41501195.
  13. ^ Beichman, Charles; Hirano, Teruyuki; David, Trevor J.; Kotani, Takayuki; Hillenbrand, Lynne A.; Vasisht, Gautam; Ciardi, David R.; Harakawa, Hiroki; Kudo, Tomoyuki; Omiya, Masashi; Kuzuhara, Masayuki (June 2019). "A Mass Limit for the Young Transiting Planet V1298 Tau b". Research Notes of the AAS. 3 (6): 89. Bibcode:2019RNAAS...3...89B. doi:10.3847/2515-5172/ab2c9d. ISSN 2515-5172. S2CID 198445373.
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  15. ^ Alam, Munazza K.; Kirk, James; Dos Santos, Leonardo A.; McCreery, Patrick; Allan, Andrew P.; Owen, James E.; Vidotto, Aline A.; Allart, Romain; Bourrier, Vincent; Espinoza, Néstor; King, George W.; López-Morales, Mercedes; Seidel, Julia V. (September 2024). "Nondetections of Helium in the Young Sub-Jovian Planets K2-100b, HD 63433b, and V1298 Tau c". The Astronomical Journal. 168 (3): 102. arXiv:2405.17294. Bibcode:2024AJ....168..102A. doi:10.3847/1538-3881/ad50d4. ISSN 0004-6256.{{cite journal}}: CS1 maint: unflagged free DOI (link)
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  17. ^ Barat, Saugata; Désert, Jean-Michel; Vazan, Allona; Baeyens, Robin; Line, Michael R.; Fortney, Jonathan J.; David, Trevor J.; Livingston, John H.; Jacobs, Bob; Panwar, Vatsal; Shivkumar, Hinna; Todorov, Kamen O.; Pino, Lorenzo; Mraz, Georgia; Petigura, Erik A. (2024-07-01). "The metal-poor atmosphere of a potential sub-Neptune progenitor". Nature Astronomy. 8 (7): 899–908. arXiv:2312.16924. Bibcode:2024NatAs...8..899B. doi:10.1038/s41550-024-02257-0. ISSN 2397-3366.
  18. ^ Barat, Saugata; Désert, Jean-Michel; Goyal, Jayesh M.; Vazan, Allona; Kawashima, Yui; Fortney, Jonathan J.; Bean, Jacob L.; Line, Michael R.; Panwar, Vatsal (2024-07-01), "First comparative exoplanetology within a transiting multi-planet system: Comparing the atmospheres of V1298 Tau b and C", Astronomy & Astrophysics, 692: A198, arXiv:2407.14995, doi:10.1051/0004-6361/202451127
  19. ^ Barat, Saugata; Désert, Jean-Michel; Mukherjee, Sagnick; Goyal, Jayesh M.; Xue, Qiao; Kawashima, Yui; Vazan, Allona; Misener, William; Schlichting, Hilke E.; Fortney, Jonathan J.; Bean, Jacob L.; Avarsekar, Swaroop; Henry, Gregory W.; Baeyens, Robin; Line, Michael R. (September 2025). "A Metal-poor Atmosphere with a Hot Interior for a Young Sub-Neptune Progenitor: JWST/NIRSpec Transmission Spectrum of V1298 Tau b". The Astronomical Journal. 170 (3): 165. arXiv:2507.08837. Bibcode:2025AJ....170..165B. doi:10.3847/1538-3881/adec89. ISSN 0004-6256.{{cite journal}}: CS1 maint: unflagged free DOI (link)
  20. ^ Sikora, James; Rowe, Jason; Barat, Saugata; Bean, Jacob L.; Brady, Madison; Désert, Jean-Michel; Feinstein, Adina D.; Gilbert, Emily A.; Henry, Gregory; Kasper, David; Lizotte, Déreck-Alexandre; Matesic, Michael R. B.; Panwar, Vatsal; Seifahrt, Andreas; Shivkumar, Hinna (2023-06-01). "Updated Planetary Mass Constraints of the Young V1298 Tau System Using MAROON-X". The Astronomical Journal. 165 (6): 250. arXiv:2304.00797. Bibcode:2023AJ....165..250S. doi:10.3847/1538-3881/acc865. ISSN 0004-6256.
  21. ^ Damasso, M.; Scandariato, G.; Nascimbeni, V.; Nardiello, D.; Mancini, L.; Marino, G.; Bruno, G.; Brandeker, A.; Leto, G.; Marzari, F.; Lanza, A. F.; Benatti, S.; Desidera, S.; Béjar, V. J. S.; Biagini, A. (2023-12-01). "Photometric follow-up of the 20 Myr old multi-planet host star V1298 Tau with CHEOPS and ground-based telescopes". Astronomy and Astrophysics. 680: A8. arXiv:2309.14131. Bibcode:2023A&A...680A...8D. doi:10.1051/0004-6361/202346840. ISSN 0004-6361.
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