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β Hydrae
	; A light curve for Beta Hydrae plotted from TESS data
	Location of β Hydrae (circled)
Observation data; Epoch J2000.0 Equinox J2000.0 (ICRS)
Constellation	Hydra
Right ascension	11h 52m 54.52149s
Declination	−33° 54′ 29.2672″
Apparent magnitude (V)	4.29 (combined) (4.67 + 5.47)
Characteristics
Spectral type	B9IIIp Si + ?; kB8hB8HeA0VSi
U−B color index	−0.34
B−V color index	−0.100±0.003
R−I color index	−0.08
Variable type	α2 CVn
Astrometry
Radial velocity (Rv)	−1.0±3.7 km/s
Proper motion (μ)	RA: −56.56 mas/yr ; Dec.: +0.19 mas/yr
Parallax (π)	10.53 ± 0.60 mas
Distance	310 ± 20 ly ; (95 ± 5 pc)
Absolute magnitude (MV)	−0.59
Details
A
Mass	3.36±0.15 M☉
Radius	3.89±0.08 R☉
Luminosity	257+45; −38 L☉
Surface gravity (log g)	2.52±0.03 cgs
Temperature	10,980±110 K
Rotation	2.35666±0.00002 d
Age	178+62; −12 Myr
B
Mass	~3 M☉
Other designations
	Beta Hydrae, Beta Hya, HJ 4478AB, β Hya, CD−33°8018, CPD−33°3159, GC 16258, HD 103192, HIP 57936, HR 4552, SAO 202901, PPM 289465, CCDM J11529-3354AB, WDS 11529-3354AB
Database references
SIMBAD	data
	A
	B

Beta Hydrae, Latinized from β Hydrae, is a double star in the equatorial constellation of Hydra.^[14] Historically, Beta Hydrae was designated 28 Crateris, but the latter fell out of use when the IAU defined the permanent constellation boundaries in 1930.^[15] The system is faintly visible to the naked eye with a combined apparent visual magnitude that ranges around 4.29.^[3] It is located at a distance of approximately 310 light years from the Sun based on parallax.

The double nature of this system was first reported by English astronomer John Herschel in 1834.^[16] The brighter primary, designated component A, has an average visual magnitude of 4.67, while the secondary, component B, is of magnitude 5.47. As of 2002, the secondary is located at an angular separation of 0.65 arcseconds from the primary, along a position angle of 28.5°.^[4]

The brighter component is an α² Canum Venaticorum variable that changes in brightness with a period of 2.344 days and an amplitude of 0.04 in visual magnitude.^[8] It is a magnetic chemically-peculiar star^[17] with an average quadratic field strength of (−206±68)×10⁻⁴ T.^[12] The star is around 178 million years old^[11] with 3.4^[9] times the mass of the Sun and 3.9^[10] times the Sun's radius. On average, it is radiating 257^[11] times the luminosity of the Sun from its photosphere at an effective temperature of 10,980 K.^[10]

In 1972, M. R. Molnar found a stellar classification of B9IIIp Si for β Hydrae A, showing an abundance anomaly for silicon.^[5] R. F. Garrison and R. O. Gray assigned it a class of kB8hB8HeA0VSi in 1994.^[6] This notation indicates the Calcium K line matches a star of class B8, the hydrogen lines also match a B8 spectrum, while the helium lines match an A-type main-sequence star of class A0V.^[18] They noted that the hydrogen lines have "curious rounded profiles".^[6] Later studies list abundance anomalies of silicon, chromium, and strontium.^[19]

Cultural significance

The Kalapalo people of Mato Grosso state in Brazil called this star and ψ Hya Kafanifani.^[20]

References

^ "MAST: Barbara A. Mikulski Archive for Space Telescopes". Space Telescope Science Institute. Retrieved 8 December 2021.
^ ^a ^b ^c ^d ^e van Leeuwen, F. (November 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 ^c ^d ^e ^f 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 Fabricius, C.; et al. (2002). "The Tycho double star catalogue". Astronomy and Astrophysics. 384: 180–189. Bibcode:2002A&A...384..180F. doi:10.1051/0004-6361:20011822.
^ ^a ^b Molnar, Michael R. (July 1972). "The Helium-Weak Stars". Astrophysical Journal. 175: 453. Bibcode:1972ApJ...175..453M. doi:10.1086/151570.
^ ^a ^b ^c Garrison, R. F.; Gray, R. O. (April 1994). "The late B-type stars: refined MK classification, confrontation with Stromgren photometry, and the effects of rotation". Astronomical Journal. 107: 1556. Bibcode:1994AJ....107.1556G. doi:10.1086/116967.
^ Hoffleit, D.; Warren, Jr., W. H. "HR 4552, database entry". The Bright Star Catalogue (5th Revised (Preliminary Version) ed.). Centre de Données astronomiques de Strasbourg. Retrieved 2020-12-31. ID V/50. Accessed on line September 23, 2008.
^ ^a ^b Samus', N. N; Kazarovets, E. V; Durlevich, O. V; Kireeva, N. N; Pastukhova, E. N (2017). "General catalogue of variable stars: Version GCVS 5.1". Astronomy Reports. 61 (1): 80. Bibcode:2017ARep...61...80S. doi:10.1134/S1063772917010085. S2CID 125853869.
^ ^a ^b North, P. (June 1998). "Do SI stars undergo any rotational braking?". Astronomy and Astrophysics. 334: 181–187. arXiv:astro-ph/9802286. Bibcode:1998A&A...334..181N.
^ ^a ^b ^c ^d ^e Arcos, C.; Kanaan, S.; Chávez, J.; Vanzi, L.; Araya, I.; Curé, M. (March 2018). "Stellar parameters and H α line profile variability of Be stars in the BeSOS survey". Monthly Notices of the Royal Astronomical Society. 474 (4): 5287–5299. arXiv:1711.08675. Bibcode:2018MNRAS.474.5287A. doi:10.1093/mnras/stx3075.
^ ^a ^b ^c ^d Sikora, J.; et al. (February 2019). "A volume-limited survey of mCP stars within 100 pc - I. Fundamental parameters and chemical abundances". Monthly Notices of the Royal Astronomical Society. 483 (2): 2300–2324. arXiv:1811.05633. Bibcode:2019MNRAS.483.2300S. doi:10.1093/mnras/sty3105.
^ ^a ^b Sikora, J.; et al. (March 2019). "A volume-limited survey of mCP stars within 100 pc II: rotational and magnetic properties". Monthly Notices of the Royal Astronomical Society. 483 (3): 3127–3145. arXiv:1811.05635. Bibcode:2019MNRAS.483.3127S. doi:10.1093/mnras/sty2895.
^ Kaler, James B. (July 4, 2015). "Beta Hydrae". Stars. Retrieved 2020-12-31.
^ ^a ^b "bet hya". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2020-12-31.
^ Wagman, M. (August 1987). "Flamsteed's Missing Stars". Journal for the History of Astronomy. 18 (3): 216. Bibcode:1987JHA....18..209W. doi:10.1177/002182868701800305. S2CID 118445625.
^ Mason, B. D.; et al. (2014), "The Washington Visual Double Star Catalog", The Astronomical Journal, 122 (6): 3466–3471, Bibcode:2001AJ....122.3466M, doi:10.1086/323920.
^ Bychkov, V. D.; et al. (August 2003). "Catalogue of averaged stellar effective magnetic fields. I. Chemically peculiar A and B type stars". Astronomy and Astrophysics. 407 (2): 631–642. arXiv:astro-ph/0307356. Bibcode:2003A&A...407..631B. doi:10.1051/0004-6361:20030741. S2CID 14184105.
^ Gray, Richard O.; Corbally, Christopher J. (2009). Stellar Spectral Classification. Princeton University Press. pp. 176–183. ISBN 978-0691125114.
^ Mikulášek, Z.; et al. (January 2007). "On-line database of photometric observations of magnetic chemically peculiar stars". Astronomische Nachrichten. 328 (1): 10–15. Bibcode:2007AN....328...10M. doi:10.1002/asna.200610705.
^ Basso, Ellen B. (1987). In Favor of Deceit: A Study of Tricksters in an Amazonian Society. Tucson, Arizona: University of Arizona Press. p. 360. ISBN 0-8165-1022-9.