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Tau1 Hydrae 
Summary
Tau1 Hydrae is a triple star[3] system in the equatorial constellation of Hydra. Based upon the annual parallax shift of the two visible components as seen from Earth,[1] they are located about 18 parsecs (59 ly) from the Sun. The system has a combined apparent visual magnitude of +4.59,[2] which is bright enough to be visible to the naked eye at night.
| Observation data Epoch 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−V color index | +0.411±0.015[2] |
| Astrometry | |
| Radial velocity (Rv) | +10.85±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 (17.8 ± 0.2 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 (18.06 ± 0.02 pc) |
| Orbit[8] | |
| Period (P) | 2,807±23 d |
| Eccentricity (e) | 0.33±0.12 |
| Periastron epoch (T) | 2445260 ± 150 JD |
| Semi-amplitude (K1) (primary) | 2.98±0.39 km/s |
| Details | |
| τ1 Hydrae A | |
| Mass | 1.20[9] M☉ |
| Radius | 1.4[10] R☉ |
| Luminosity (bolometric) | 3.369[2] L☉ |
| Surface gravity (log g) | 4.12±0.14[9] cgs |
| Temperature | 6,473±220[9] K |
| Metallicity [Fe/H] | −0.01[2] dex |
| Rotational velocity (v sin i) | 30.4±1.5[5] km/s |
| 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 | |
| Database references | |
| SIMBAD | τ1 Hya AB |
| τ1 Hya A | |
| τ1 Hya B | |
The inner pair of stars form a single-lined spectroscopic binary with an orbital period of about 2,807 days and an eccentricity of 0.33.[8] The visible member of the pair, component A, is a visual magnitude 4.60[2] F-type main sequence star with a stellar classification of F6 V.[3] During the 1990s, it was thought to be a Gamma Doradus variable, but this was later discounted as it shows no short-term photometric variability. The star does show some long-term variability, possibly as a result of a magnetic activity cycle similar to the solar cycle.[13]
The tertiary member, component B, is a visual magnitude 7.15[2] K-type star with a class of K0.[3] It lies at a separation of 1,120 AU from the primary.[14] As of 2012, it was positioned at an angular separation of 67.5 arc seconds along a position angle of 4°.[15]
References edit
- ^ 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 at VizieR.
- ^ 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 at VizieR.
- ^ 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. Retrieved 2017-03-22.
{{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.