Tau5 Eridani

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τ5 Eridani
Eridanus constellation map.svg
link=τ5 Eri

Location of τ5 Eridani (circled)
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Eridanus
Right ascension 03h 33m 47.27613s[1]
Declination −21° 37′ 58.3830″[1]
Apparent magnitude (V) 4.26[2]
Spectral type B0 V + B9 V[3]
U−B color index 0.35[2]
B−V color index −0.09[2]
Proper motion (μ) RA: +44.94[1] mas/yr
Dec.: −28.16[1] mas/yr
Parallax (π) 11.12 ± 0.21[1] mas
Distance 293 ± 6 ly
(90 ± 2 pc)
Absolute magnitude (MV) −0.51[4]
Period (P) 6.2236 d
Eccentricity (e) 0.2
Periastron epoch (T) 2424446.548 JD
Argument of periastron (ω)
Semi-amplitude (K1)
107 km/s
Semi-amplitude (K2)
103 km/s
τ5 Eri A
Mass 3.30+0.24
[6] M
Radius 3.2[3] R
Luminosity 188[7] L
Surface gravity (log g) 4.00±0.15[6] cgs
Temperature 12,514±425[8] K
Rotational velocity (v sin i) 55±8[3] km/s
Age 157+23
[6] Myr
τ5 Eri B
Radius 2.6[3] R
Rotational velocity (v sin i) 50±8[3] km/s
Other designations
τ5 Eridani, τ5 Eri, 19 Eridani, BD-22° 628, HD 22203, HIP 16611, HR 1088, SAO 168634.[9]
Database references

Tau5 Eridani, Latinized from τ5 Eridani, is a binary star system in the constellation Eridanus. It is visible to the naked eye with a combined apparent visual magnitude of 4.26.[2] The distance to this system, as estimated using the parallax technique, is around 293 light years.[1]

Tau5 Eridani is a double-lined spectroscopic binary system.[10] The two stars orbit each other closely with a period of 6.2 days and an eccentricity of 0.2.[5] On average, the two stars are separated by around 0.183 AU.[3]

The primary component is a B-type main sequence star with a stellar classification of B0 V.[3] It is around 157 million years old and is spinning with a projected rotational velocity of 55 km/s.[3] The star has around 3.3[6] times the mass of the Sun and 3.2[3] times the Sun's radius. It radiates 188[7] times the solar luminosity from an outer atmosphere at an effective temperature of 12,514 K.[8]

The secondary component has a stellar classification of B9 V.[3] It is slightly smaller, with an estimated size equal to 2.6 times the radius of the Sun.[3]

Although τ5 Eridani has no bright visual companion stars, the galaxy IC 1953 is less than 10' away. It is one of the brighter members of a loose group of galaxies called the Eridanus Group scattered around the components of τ Eridani.


  1. ^ a b c d e f van Leeuwen, F. (2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics, 474 (2): 653–664, arXiv:0708.1752Freely accessible, Bibcode:2007A&A...474..653V, doi:10.1051/0004-6361:20078357. 
  2. ^ a b c d Mermilliod, J.-C. (1986), Compilation of Eggen's UBV data, transformed to UBV (unpublished), SIMBAD, Bibcode:1986EgUBV........0M. 
  3. ^ a b c d e f g h i j k Howe, K. S.; Clarke, C. J. (January 2009), "An analysis of v sin (i) correlations in early-type binaries", Monthly Notices of the Royal Astronomical Society, 392 (1): 448–454, Bibcode:2009MNRAS.392..448H, doi:10.1111/j.1365-2966.2008.14073.x. 
  4. ^ Anderson, E.; Francis, Ch. (2012), "XHIP: An extended hipparcos compilation", Astronomy Letters, 38 (5): 331, arXiv:1108.4971Freely accessible, Bibcode:2012AstL...38..331A, doi:10.1134/S1063773712050015. 
  5. ^ a b Pourbaix, D.; et al. (2004), "SB9: The ninth catalogue of spectroscopic binary orbits", Astronomy and Astrophysics, 424 (2): 727, arXiv:astro-ph/0406573Freely accessible, Bibcode:2004A&A...424..727P, doi:10.1051/0004-6361:20041213. 
  6. ^ a b c d Gullikson, Kevin; et al. (August 2016), "The Close Companion Mass-ratio Distribution of Intermediate-mass Stars", The Astronomical Journal, 152 (2): 13, arXiv:1604.06456Freely accessible, Bibcode:2016AJ....152...40G, doi:10.3847/0004-6256/152/2/40, 40. 
  7. ^ a b McDonald, I.; et al. (2012), "Fundamental Parameters and Infrared Excesses of Hipparcos Stars", Monthly Notices of the Royal Astronomical Society, 427 (1): 343–57, arXiv:1208.2037Freely accessible, Bibcode:2012MNRAS.427..343M, doi:10.1111/j.1365-2966.2012.21873.x. 
  8. ^ a b 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:1501.03154Freely accessible, Bibcode:2015ApJ...804..146D, doi:10.1088/0004-637X/804/2/146. 
  9. ^ "tau05 Eri -- Spectroscopic binary", SIMBAD Astronomical Database, Centre de Données astronomiques de Strasbourg, retrieved 2016-10-13. 
  10. ^ van Rensbergen, W.; et al. (February 2006), "Evolution of interacting binaries with a B type primary at birth", Astronomy and Astrophysics, 446 (3): 1071–1079, Bibcode:2006A&A...446.1071V, doi:10.1051/0004-6361:20053543.