YZ Ceti

YZ Ceti is a red dwarf star in the constellation Cetus. Although it is relatively close to the Sun at just 12 light years, this star cannot be seen with the naked eye. It is classified as a flare star that undergoes intermittent fluctuations in luminosity. YZ Ceti is about 13 percent the mass of the Sun and 17% of its radius.

YZ Ceti

Location of YZ Ceti, click for larger image.
Observation data
Epoch J2000      Equinox J2000
Constellation Cetus
Right ascension 01h 12m 30.6369s[1]
Declination −16° 59′ 56.358″[1]
Apparent magnitude (V) 12.03 - 12.18[2]
Characteristics
Evolutionary stage red dwarf
Spectral type M4.0Ve[3]
U−B color index +1.430[4]
B−V color index +1.811[4]
Variable type Flare star[5]
Astrometry
Radial velocity (Rv)+28.09[6] km/s
Proper motion (μ) RA: 1,205.074[1] mas/yr
Dec.: 637.547[1] mas/yr
Parallax (π)269.0573 ± 0.0337 mas[1]
Distance12.122 ± 0.002 ly
(3.7167 ± 0.0005 pc)
Absolute magnitude (MV)14.30[3]
Details
Mass0.130±0.013[7] M☉
Radius0.168±0.009[7] R☉
Luminosity0.002195[8] L☉
Surface gravity (log g)5.20[8] cgs
Temperature3056±60[7] K
Metallicity [Fe/H]−0.26±0.08[7] dex
Rotation68.3 d[9]
Rotational velocity (v sin i)3.40[10] km/s
Age5.0±1.0[7] Gyr
Other designations
GCTP 248.01, GJ 54.1, HIP 5643, G 268-135, L 725-32, LHS 138, LTT 670, 2MASS J01123052-1659570
Database references
SIMBADdata

This star is unusually close to Tau Ceti, a star of spectral class G8. The two are only about 1.6 light years apart,[11] a little more than a third of the distance from the Sun to the Solar System's nearest neighbor, Proxima Centauri.

Variability
A visual band light curve for YZ Ceti, adapted from Jayasinghe et al. (2017)[9]

YZ Ceti is a variable star designation: the star shows occasional rapid and brief increases in brightness, sometimes reaching magnitude 12.03, caused by eruptions from the surface. This type of variable star is known as a UV Ceti star after its first member, or more colloquially as a flare star.

YZ Ceti also shows small periodic variations in brightness caused by starspots or chromospheric features moving as the star rotates. This class of variable stars are known as BY Draconis variables.[2] The periodic variations allow the rotational period of the star to be measured at 68.3 days, although modelling of its planetary system gives a rotational period for the star of 83 days.[9]

Planetary system

On 10 August 2017 three planets were announced to have been discovered around YZ Ceti and a possible fourth sub-Earth planet candidate, still needing confirmation, with 0.472±0.096 Earth masses at an orbital period of 1.04 days. The orbits of the three confirmed planets were determined to be too close to YZ Ceti to be within the star's habitable zone, with equilibrium temperatures ranging from 347–491 K (74–218 °C; 165–424 °F), 299–423 K (26–150 °C; 79–302 °F), and 260–368 K (−13–95 °C; 8–203 °F) for planets b, c, and d, respectively.[7]

An August 2018 study reexamined the discovery measurements, confirming the orbit of YZ Ceti d, but finding a possibly marginally longer orbital period of YZ Ceti b of 2.02 days rather than 1.97 days, and additionally finding that YZ Ceti c probably orbits in only 0.75 days rather than 3.06 days. If the latter is true, YZ Ceti c would have a mass of only 0.58 Earth masses and a roughly 10% chance of transiting YZ Ceti.[12] However, a 2020 study did not support the latter conclusion, finding the 0.75-day period to be an alias of the true 3.06-day period. It also did not find evidence for the fourth candidate planet.[13]

Two 2023 studies detected bursts of radiation in radio wavelengths from YZ Ceti, which is likely associated with interaction of the innermost planet, YZ Ceti b, with the star as well as evidence for the presence of magnetic fields. It may be the first detection of a magnetic field generated by a terrestrial exoplanet.[14][15][16][17]

The YZ Ceti planetary system[13]
Companion
(in order from star)		 Mass Semimajor axis
(AU)		 Orbital period
(days)		 Eccentricity Inclination Radius
b ≥0.70+0.09
−0.08 M🜨		 0.01634+0.00035
−0.00041		 2.02087+0.00007
−0.00009		 0.06+0.06
−0.04		 — —
c ≥1.14+0.11
−0.10 M🜨		 0.02156+0.00046
−0.00054		 3.05989+0.00010
−0.00010		 0.00 — —
d ≥1.09+0.12
−0.12 M🜨		 0.02851+0.00061
−0.00071		 4.65626+0.00028
−0.00029		 0.07+0.04
−0.05		 — —

See also

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. Watson, C. L. (2006). "The International Variable Star Index (VSX)". The Society for Astronomical Sciences 25th Annual Symposium on Telescope Science. Held May 23–25. 25: 47. Bibcode:2006SASS...25...47W.
  3. Davison, Cassy L; White, R. J; Henry, T. J; Riedel, A. R; Jao, W.-C; Bailey, J. I; Quinn, S. N; Cantrell, J. R; Subasavage, J. P; Winters, J. G (2015). "A 3D Search for Companions to 12 Nearby M Dwarfs". The Astronomical Journal. 149 (3): 106. arXiv:1501.05012. Bibcode:2015AJ....149..106D. doi:10.1088/0004-6256/149/3/106. S2CID 9719725.
  4. Koen, C; Kilkenny, D; Van Wyk, F; Marang, F (2010). "UBV(RI)C JHK observations of Hipparcos-selected nearby stars". Monthly Notices of the Royal Astronomical Society. 403 (4): 1949. Bibcode:2010MNRAS.403.1949K. doi:10.1111/j.1365-2966.2009.16182.x.
  5. 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. Bibcode:2009yCat....102025S.
  6. Nidever, David L; Marcy, Geoffrey W; Butler, R. Paul; Fischer, Debra A; Vogt, Steven S (2002). "Radial Velocities for 889 Late-Type Stars". The Astrophysical Journal Supplement Series. 141 (2): 503–522. arXiv:astro-ph/0112477. Bibcode:2002ApJS..141..503N. doi:10.1086/340570. S2CID 51814894.
  7. Astudillo-Defru, Nicola; Díaz, Rodrigo F.; Bonfils, Xavier; Almenara, José M.; Delisle, Jean-Baptiste; Bouchy, François; Delfosse, Xavier; Forveille, Thierry; Lovis, Christophe; Mayor, Michel; Murgas, Felipe; Pepe, Francesco; Santos, Nuno C.; Ségransan, Damien; Udry, Stéphane; Wünsche, Anaël (2017). "The HARPS search for southern extra-solar planets. XLII. A system of Earth-mass planets around the nearby M dwarf YZ Ceti". Astronomy & Astrophysics. 605: L11. arXiv:1708.03336. Bibcode:2017A&A...605L..11A. doi:10.1051/0004-6361/201731581. S2CID 119393757.
  8. Schweitzer, A.; et al. (May 2019). "The CARMENES search for exoplanets around M dwarfs. Different roads to radii and masses of the target stars". Astronomy & Astrophysics. 625: 16. arXiv:1904.03231. Bibcode:2019A&A...625A..68S. doi:10.1051/0004-6361/201834965. S2CID 102351979. A68.
  9. Jayasinghe, T; Stanek, K. Z; Kochanek, C. S; Holoien, T. W.-S; Shields, J. V; Thompson, T. A; Shappee, B. J; Prieto, J. L; Dong, Subo (2017). "ASAS-SN V-band Light Curve of Multi-Planet M-dwarf Host YZ Cet Reveals a Rotation Period of 68 Days". The Astronomer's Telegram. 0643: 1. Bibcode:2017ATel10643....1J.
  10. Fouqué, Pascal; et al. (April 2018). "SPIRou Input Catalogue: global properties of 440 M dwarfs observed with ESPaDOnS at CFHT". Monthly Notices of the Royal Astronomical Society. 475 (2): 1960–1986. arXiv:1712.04490. Bibcode:2018MNRAS.475.1960F. doi:10.1093/mnras/stx3246.
  11. Page of Tau Ceti, see the chapter of Closest Neighbors, for YZ Ceti.
  12. Robertson, Paul (2018). "Aliasing in the Radial Velocities of YZ Ceti: An Ultra-short Period for YZ Ceti c?". The Astrophysical Journal. 864 (2): L28. arXiv:1808.07059. Bibcode:2018ApJ...864L..28R. doi:10.3847/2041-8213/aadc0b. S2CID 119373170.
  13. Stock, S.; et al. (2020). "The CARMENES search for exoplanets around M dwarfs". Astronomy & Astrophysics. 636: A119. arXiv:2002.01772. Bibcode:2020A&A...636A.119S. doi:10.1051/0004-6361/201936732. S2CID 211032169.
  14. Pineda, J. Sebastian; Villadsen, Jackie (April 2023). "Coherent radio bursts from known M-dwarf planet host YZ Ceti". Nature Astronomy. 7: 569–578. arXiv:2304.00031. Bibcode:2023NatAs...7..569P. doi:10.1038/s41550-023-01914-0.
  15. Trigilio, Corrado; Biswas, Ayan; et al. (May 2023). "Star-Planet Interaction at radio wavelengths in YZ Ceti: Inferring planetary magnetic field". arXiv:2305.00809 [astro-ph.EP].
  16. "A magnetic field on a nearby Earth-sized exoplanet?". earthsky.org. 2023-04-10. Retrieved 2023-08-07.
  17. O'Callaghan, Jonathan (7 August 2023). "Exoplanets Could Help Us Learn How Planets Make Magnetism". Quanta Magazine.
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