Star in the constellation Cetus
2 Ceti , also namedHydor ,[ 13] [ 14] star in theequatorial constellation ofCetus , near the border withAquarius . It is visible to the naked eye with anapparent visual magnitude of 4.483.[ 2] parallax shift of[ 1] light years . It appears to be moving further from the Earth with a heliocentricradial velocity of about +8 km/s.[ 8]
Thestellar classification for this star is B9 IVn,[ 5] B-type subgiant star with "nebulous"absorption lines due to rapid rotation.[ 15] [ 4] [ 11] equatorial bulge that is 12% larger than the polar radius.[ 15] [ 10] mass of the Sun and 3.9 times theSun's radius .[ 9] Sun's luminosity [ 4] photosphere at aneffective temperature of 11,419 K.[ 10] infrared excess has been detected around this star by theAkari satellite at a wavelength of 18μm, suggesting there is an orbitingdebris disk .[ 16]
The ancient Greek term Hydor (ὕδωρ [ 17] IAU Working Group on Star Names approved the name Hydor for 2 Ceti, on 25 August 2025 and it is now so entered in the IAU Catalog of Star Names;[ 13] λ Aquarii , for which the IAU adopted the Indian nameShatabhisha .[ 17]
^a b c d e f van Leeuwen, F. (2007). "Validation of the new Hipparcos reduction".Astronomy and Astrophysics .474 (2):653– 664.arXiv :0708.1752 Bibcode :2007A&A...474..653V .doi :10.1051/0004-6361:20078357 .S2CID 18759600 . ^a b Høg, E.; et al. (2000). "The Tycho-2 catalogue of the 2.5 million brightest stars".Astronomy and Astrophysics .355 :L27– L30.Bibcode :2000A&A...355L..27H . ^ 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 atVizieR .^a b c d e Zorec, J.; et al. (2012). "Rotational velocities of A-type stars. IV. Evolution of rotational velocities".Astronomy and Astrophysics .537 : A120.arXiv :1201.2052 Bibcode :2012A&A...537A.120Z .doi :10.1051/0004-6361/201117691 .S2CID 55586789 . ^a b c Wu, Yue; et al. (2010). "Coudé-feed stellar spectral library – atmospheric parameters".Astronomy & Astrophysics .525 : A71.arXiv :1009.1491 Bibcode :2011A&A...525A..71W .doi :10.1051/0004-6361/201015014 .S2CID 53480665 . ^ Nicolet, B. (1964). "Catalogue of homogeneous data in the UBV photoelectric photometric system".Astronomy and Astrophysics Supplement Series .34 :1– 49.Bibcode :1978A&AS...34....1N . ^a b Anderson, E.; Francis, Ch. (2012), "XHIP: An extended hipparcos compilation",Astronomy Letters ,38 (5): 331,arXiv :1108.4971 Bibcode :2012AstL...38..331A ,doi :10.1134/S1063773712050015 ,S2CID 119257644 . ^a b Gontcharov, G. A. (2006). "Pulkovo Compilation of Radial Velocities for 35 495 Hipparcos stars in a common system".Astronomy Letters .32 (11):759– 771.arXiv :1606.08053 Bibcode :2006AstL...32..759G .doi :10.1134/S1063773706110065 .S2CID 119231169 . ^a b c d Stassun, Keivan G.; et al. (2019)."The Revised TESS Input Catalog and Candidate Target List" .The Astronomical Journal .158 (4): 138.arXiv :1905.10694 Bibcode :2019AJ....158..138S .doi :10.3847/1538-3881/ab3467 ^a b c d David, Trevor J.; Hillenbrand, Lynne A. (2015). "The Ages of Early-Type Stars: Strömgren Photometric Methods Calibrated, Validated, Tested, and Applied to Hosts and Prospective Hosts of Directly Imaged Exoplanets".The Astrophysical Journal .804 (2): 146.arXiv :1501.03154 Bibcode :2015ApJ...804..146D .doi :10.1088/0004-637X/804/2/146 .S2CID 33401607 . ^a b Royer, F.; et al. (2007). "Rotational velocities of A-type stars".Astronomy and Astrophysics .463 (2): 671.arXiv :astro-ph/0610785 Bibcode :2007A&A...463..671R .doi :10.1051/0004-6361:20065224 .S2CID 18475298 . ^ "2 Cet" .SIMBAD Centre de données astronomiques de Strasbourg . RetrievedDecember 23, 2018 .^a b "IAU Catalog of Star Names" . Retrieved26 August 2025 .^ Chini, R.; et al. (2012)."A spectroscopic survey on the multiplicity of high-mass stars" .Monthly Notices of the Royal Astronomical Society .424 (3):1925– 1929.arXiv :1205.5238 Bibcode :2012MNRAS.424.1925C .doi :10.1111/j.1365-2966.2012.21317.x S2CID 119120749 . ^a b van Belle, Gerard T. (March 2012). "Interferometric observations of rapidly rotating stars".The Astronomy and Astrophysics Review .20 (1): 51.arXiv :1204.2572 Bibcode :2012A&ARv..20...51V .doi :10.1007/s00159-012-0051-2 .S2CID 119273474 . ^ Ishihara, Daisuke; et al. (May 2017). "Faint warm debris disks around nearby bright stars explored by AKARI and IRSF".Astronomy & Astrophysics .601 : 18.arXiv :1608.04480 Bibcode :2017A&A...601A..72I .doi :10.1051/0004-6361/201526215 .S2CID 55234482 . A72. ^a b "Hydor" .All Skies Encyclopaedia .IAU Working Group on Star Names . Retrieved26 August 2025 .
