Double star in the constellation Hydra
β Hydrae Location of β Hydrae (circled)
Observation dataEpoch J2000.0 Equinox J2000.0 (ICRS ) Constellation Hydra [ 1] Right ascension 11h 52m 54.52149s [ 2] Declination −33° 54′ 29.2672″[ 2] Apparent magnitude (V)4.29(combined) [ 1] (4.67 + 5.47) [ 3] Characteristics Spectral type B9IIIp Si[ 4] [ 5] U−Bcolor index −0.34[ 1] B−Vcolor index ± 0.003[ 1] R−Icolor index −0.08[ 6] Variable type α2 CVn [ 7] Astrometry Radial velocity (Rv )−± 3.7[ 1] km/s Proper motion (μ)RA: −56.56[ 2] mas /yr Dec.: +0.19[ 2] mas /yr Parallax (π)10.53± 0.60 mas [ 2] Distance 310 ± 20 ly pc ) Absolute magnitude (MV )−0.59[ 1] Details A Mass ± 0.15[ 8] M ☉ Radius ± 0.08[ 9] R ☉ Luminosity +45 [ 10] L ☉ Surface gravity (log g )± 0.03[ 9] cgs Temperature ± 110[ 9] K Rotation ± 0.00002 d[ 11] Age +62 [ 10] Myr B Mass ~3[ 12] M ☉ Other designations Beta Hydrae, Beta Hya,HJ 4478AB ,β Hya ,CD −33°8018CPD −33°3159GC 16258HD 103192HIP 57936HR 4552SAO 202901PPM 289465CCDM J11529-3354ABWDS 11529-3354AB[ 13] Database references SIMBAD data A B
light curve for Beta Hydrae plotted fromTESS [ 14] Beta Hydrae , Latinized fromβ Hydrae , is adouble star in theequatorial constellation ofHydra .[ 13] 28 Crateris , but the latter fell out of use when theIAU defined the permanent constellation boundaries in 1930.[ 15] apparent visual magnitude that ranges around 4.29.[ 1] light years from theSun based onparallax .
The double nature of this system was first reported by English astronomerJohn Herschel in 1834.[ 16] angular separation ofarcseconds position angle of 28.5°.[ 3]
The brighter component is anα2 Canum Venaticorum variable that changes in brightness with a period of 2.344 days and an amplitude of 0.04 in visual magnitude.[ 7] magnetic chemically-peculiar star [ 17] ± 68)× 10−4 T [ 11] [ 10] [ 8] mass of the Sun and 3.9[ 9] Sun's radius . On average, it is radiating 257[ 10] luminosity of the Sun from itsphotosphere at aneffective temperature of 10,980 K.[ 9]
In 1972, M. R. Molnar found astellar classification of B9IIIp Si for β Hydrae A, showing an abundance anomaly for silicon.[ 4] [ 5] Calcium K line matches a star of class B8, thehydrogen lines also match a B8spectrum , while the helium lines match anA-type main-sequence star of class A0V.[ 18] [ 5] [ 19]
Cultural significance [ edit ] TheKalapalo people ofMato Grosso state in Brazil called this star andψ Hya Kafanifani .[ 20]
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