Tau⁵ Eridani

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]

For other star systems with this Bayer designation, see Tau Eridani.

τ⁵ Eridani

Location of τ^5 Eridani (circled)
Observation data Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation	Eridanus
Right ascension	03^h 33^m 47.27613^s[1]
Declination	−21° 37′ 58.3830″[1]
Apparent magnitude (V)	4.26[2]
Characteristics
Spectral type	B0 V + B9 V[3]
U−B color index	0.35[2]
B−V color index	−0.09[2]
Astrometry
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]
Orbit[5]
Period (P)	6.2236 d
Eccentricity (e)	0.2
Periastron epoch (T)	2424446.548 JD
Argument of periastron (ω) (secondary)	313°
Semi-amplitude (K1) (primary)	107 km/s
Semi-amplitude (K2) (secondary)	103 km/s
Details
τ^5 Eri A
Mass	3.30+0.24 −0.20[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 −45[6] Myr
τ^5 Eri B
Radius	2.6[3] R☉
Rotational velocity (v sin i)	50±8[3] km/s
Other designations
τ^5 Eridani, τ^5 Eri, 19 Eridani, BD-22° 628, HD 22203, HIP 16611, HR 1088, SAO 168634.[9]
Database references
SIMBAD	data

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.

References

1. 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.
2. Mermilliod, J.-C. (1986), Compilation of Eggen's UBV data, transformed to UBV (unpublished), SIMBAD, Bibcode:1986EgUBV........0M.
3. 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:1108.4971, Bibcode:2012AstL...38..331A, doi:10.1134/S1063773712050015.
5. Pourbaix, D.; et al. (2004), "S_B⁹: The ninth catalogue of spectroscopic binary orbits", Astronomy and Astrophysics, 424 (2): 727, arXiv:astro-ph/0406573, Bibcode:2004A&A...424..727P, doi:10.1051/0004-6361:20041213.
6. Gullikson, Kevin; et al. (August 2016), "The Close Companion Mass-ratio Distribution of Intermediate-mass Stars", The Astronomical Journal, 152 (2): 13, arXiv:1604.06456, Bibcode:2016AJ....152...40G, doi:10.3847/0004-6256/152/2/40, 40.
7. 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:1208.2037, Bibcode:2012MNRAS.427..343M, doi:10.1111/j.1365-2966.2012.21873.x.
8. 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.
9. "tau05 Eri". SIMBAD. 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.