Triple star system in the constellation Hydra
For other stars with this Bayer designation, see
τ Hydrae .
Tau1 Hydrae Location of τ
1 Hydrae (circled in red)
Observation dataEpoch J2000.0 Equinox J2000.0 (ICRS ) Constellation Hydra Right ascension 09h 29m 08.89655s [ 1] Declination −02° 46′ 08.2649″[ 1] Apparent magnitude (V)+4.59(4.60 + 7.15) [ 2] Characteristics Spectral type F6 V + ? + K0 [ 3] B−Vcolor index ± 0.015[ 2] Astrometry Radial velocity (Rv )± 0.28[ 4] km/s Absolute magnitude (MV )+3.28[ 5] τ1 Hydrae A Proper motion (μ)RA: +107.115[ 6] mas /yr Dec.: −29.652[ 6] mas /yr Parallax (π)56.2938± 0.5309 mas [ 6] Distance 57.9 ± 0.5 ly pc ) τ1 Hydrae B Proper motion (μ)RA: +138.487[ 7] mas /yr Dec.: −17.371[ 7] mas /yr Parallax (π)55.3675± 0.0638 mas [ 7] Distance 58.91 ± 0.07 ly pc ) Orbit [ 8] Period (P)± 23 dEccentricity (e)± 0.12Periastron epoch (T)2445260 ± 150 JD Semi-amplitude 1 )± 0.39Details τ1 Hydrae A Mass 1.20[ 9] M ☉ Radius 1.4[ 10] R ☉ Luminosity (bolometric) 3.369[ 2] L ☉ Surface gravity (log g )± 0.14[ 9] cgs Temperature ± 220[ 9] K Metallicity [Fe/H] −0.01[ 2] dex Rotational velocity (v sin i )± 1.5[ 5] Age 3.61[ 2] Gyr τ1 Hydrae B Mass 0.86[ 11] M ☉ Radius 0.81[ 10] R ☉ Luminosity 0.435[ 7] L ☉ Temperature 5,197[ 7] K Other designations τ1 Hya ,31 Hydrae ,BD −02°2901,GJ 348,HD 81997,HIP 46509,HR 3759,SAO 136895,WDS J09291-0246[ 12] Database references SIMBAD τ1 Hya AB τ1 Hya A τ1 Hya B
Tau1 Hydrae is atriple star [ 3] constellation ofHydra . Based upon the annualparallax shift of the two visible components as seen from Earth,[ 1] Sun . The system has a combinedapparent visual magnitude of +4.59,[ 2]
The inner pair of stars form a single-linedspectroscopic binary with anorbital period of about 2,807 days and aneccentricity of 0.33.[ 8] [ 2] F-type main sequence star with astellar classification of F6 V.[ 3] Gamma Doradus variable , but this was later discounted as it shows no short-termphotometric variability. The star does show some long-term variability, possibly as a result of amagnetic activity cycle similar to thesolar cycle .[ 13]
The tertiary member, component B, is a visual magnitude 7.15[ 2] K-type star with a class of K0.[ 3] AU from the primary.[ 14] angular separation of 67.5 arc seconds along aposition angle of 4°.[ 15]
This star along withτ2 Hydrae ,ι Hydrae and33 Hydrae (A Hydrae) were traditionally known as Ukdah, Arabic for "knot".[ 16]
^a b c 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 c d e f g h Montesinos, B.; et al. (September 2016), "Incidence of debris discs around FGK stars in the solar neighbourhood",Astronomy & Astrophysics ,593 : 31,arXiv :1605.05837 Bibcode :2016A&A...593A..51M ,doi :10.1051/0004-6361/201628329 ,S2CID 55251562 , A51. ^a b c d Eggleton, P. P.; Tokovinin, A. A. (September 2008), "A catalogue of multiplicity among bright stellar systems",Monthly Notices of the Royal Astronomical Society 389 (2):869– 879,arXiv :0806.2878 Bibcode :2008MNRAS.389..869E ,doi :10.1111/j.1365-2966.2008.13596.x S2CID 14878976 . ^ de Bruijne, J. H. J.; Eilers, A.-C. (October 2012), "Radial velocities for the HIPPARCOS-Gaia Hundred-Thousand-Proper-Motion project",Astronomy & Astrophysics ,546 : 14,arXiv :1208.3048 Bibcode :2012A&A...546A..61D ,doi :10.1051/0004-6361/201219219 ,S2CID 59451347 , A61. ^a b Reiners, Ansgar (January 2006), "Rotation- and temperature-dependence of stellar latitudinal differential rotation",Astronomy and Astrophysics ,446 (1):267– 277,arXiv :astro-ph/0509399 Bibcode :2006A&A...446..267R ,doi :10.1051/0004-6361:20053911 ,S2CID 8642707 ^a b c Brown, A. G. A. ; et al. (Gaia collaboration ) (August 2018)."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 Gaia DR2 record for this source atVizieR .^a b c d e Brown, A. G. A. ; et al. (Gaia collaboration ) (August 2018)."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 Gaia DR2 record for this source atVizieR .^a b Pourbaix, D.; et al. (September 2004), "SB9 : The ninth catalogue of spectroscopic binary orbits",Astronomy and Astrophysics ,424 :727– 732,arXiv :astro-ph/0406573 Bibcode :2004A&A...424..727P ,doi :10.1051/0004-6361:20041213 ,S2CID 119387088 . ^a b c 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 Pasinetti Fracassini, L. E.; et al. (February 2001), "Catalogue of Apparent Diameters and Absolute Radii of Stars (CADARS)",Astronomy and Astrophysics ,367 (3rd ed.):521– 524,arXiv :astro-ph/0012289 Bibcode :2001A&A...367..521P ,doi :10.1051/0004-6361:20000451 ,S2CID 425754 . ^ Tokovinin, Andrei (2014), "From Binaries to Multiples. II. Hierarchical Multiplicity of F and G Dwarfs",The Astronomical Journal ,147 (4): 14,arXiv :1401.6827 Bibcode :2014AJ....147...87T ,doi :10.1088/0004-6256/147/4/87 ,S2CID 56066740 , 87. ^ "tau01 Hya" .SIMBAD Centre de données astronomiques de Strasbourg . Retrieved2017-03-22 .{{cite web }}: CS1 maint: postscript (link )^ Henry, G. W.; et al. (March 1999), "tau1 Hydrae: NOT A gamma DORADUS VARIABLE",Information Bulletin on Variable Stars ,4688 (4688): 1,Bibcode :1999IBVS.4688....1H . ^ Allen, Peter R.; et al. (August 2012), "Low-mass Tertiary Companions to Spectroscopic Binaries. I. Common Proper Motion Survey for Wide Companions Using 2MASS",The Astronomical Journal ,144 (2): 12,arXiv :1206.4289 Bibcode :2012AJ....144...62A ,doi :10.1088/0004-6256/144/2/62 ,S2CID 51051184 , 62. ^ 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 ^ Allen, R. H. (1963).Star Names: Their Lore and Meaning 250 .ISBN 0-486-21079-0 . Retrieved2010-12-12 .{{cite book }}:ISBN / Date incompatibility (help )
