Tau9 Eridani

τ⁹ Eridani
	; A light curve for Tau9 Eridani plotted from TESS data
Observation data; Epoch J2000.0 Equinox J2000.0 (ICRS)
Constellation	Eridanus
Right ascension	03h 59m 55.48381s
Declination	−24° 00′ 58.3798″
Apparent magnitude (V)	4.63
Characteristics
Spectral type	B9.5V Si
U−B color index	−0.40
B−V color index	−0.13
Variable type	α2 CVn
Astrometry
Radial velocity (Rv)	25.5±0.5 km/s
Proper motion (μ)	RA: +12.12 mas/yr ; Dec.: +16.48 mas/yr
Parallax (π)	9.96 ± 0.22 mas
Distance	327 ± 7 ly ; (100 ± 2 pc)
Absolute magnitude (MV)	−0.44
Orbit
Period (P)	5.95382 days
Eccentricity (e)	0.129
Periastron epoch (T)	246991.65 JD
Argument of periastron (ω); (secondary)	183.2°
Semi-amplitude (K1); (primary)	40.0 km/s
Semi-amplitude (K2); (secondary)	89.9 km/s
Details
τ9 Eri A
Mass	3.6 M☉
Radius	3.06 R☉
Luminosity	209 L☉
Surface gravity (log g)	4.11±0.11 cgs
Temperature	12,580 K
Rotational velocity (v sin i)	26.8 km/s
Age	140 Myr
τ9 Eri B
Mass	1.6 M☉
Radius	1.5 R☉
Luminosity	6.3 L☉
Temperature	7530 K
Rotational velocity (v sin i)	15 km/s
Other designations
	τ9 Eridani, τ9 Eri, 36 Eridani, CD−24° 2022, FK5 2287, HD 25267, HIP 18673, HR 1240, SAO 169017.
Database references
SIMBAD	data

Tau⁹ Eridani (τ⁹ Eri) is a binary star in the constellation Eridanus. It is visible to the naked eye with an apparent visual magnitude of 4.63.^[3] The distance to this system can be estimated using the parallax method, which yields a value of roughly 327 light years.^[3]

This is a double-lined spectroscopic binary system with an orbital period of 5.95382 days and an eccentricity of 0.12.^[7] The primary component, τ⁹ Eri A, is a magnetic chemically peculiar star^[10] with a stellar classification of B9.5V Si,^[4] indicating that it is a B-type main sequence star that shows abundance anomalies in its silicon absorption lines.^[4] It is an Alpha² Canum Venaticorum variable^[5] with a rotational periodicity of 5.954 days.^[11] The averaged strength of the stellar effective magnetic field is 240.6±91.0 G.^[4]

The primary component Tau⁹ Eridani A has an estimated 326%^[10] the mass of the Sun and 3.1 times the Sun's radius.^[8] It shines with 166^[12] times the solar luminosity from an outer atmosphere at an effective temperature of 10,866 K.^[12] The star is spinning with a projected rotational velocity of 30 km/s.^[13] The secondary star, designated Tau⁹ Eridani B, is a late A-type or early F-type star with a mass of 1.6 solar masses and an effective temperature of 7530 K.^[7]

References

^ "MAST: Barbara A. Mikulski Archive for Space Telescopes". Space Telescope Science Institute. Retrieved 8 December 2021.
^ ^a ^b ^c ^d ^e 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 Mermilliod, J.-C. (1986), "Compilation of Eggen's UBV data, transformed to UBV (unpublished)", Catalogue of Eggen's UBV Data, SIMBAD, Bibcode:1986EgUBV........0M.
^ ^a ^b ^c ^d Bychkov, V. D.; et al. (April 2009), "Catalogue of averaged stellar effective magnetic fields - II. Re-discussion of chemically peculiar A and B stars", Monthly Notices of the Royal Astronomical Society, 394 (3): 1338–1350, Bibcode:2009MNRAS.394.1338B, doi:10.1111/j.1365-2966.2008.14227.x, S2CID 120268049.
^ ^a ^b ^c Dubath, P.; et al. (2011), "Random forest automated supervised classification of Hipparcos periodic variable stars", Monthly Notices of the Royal Astronomical Society, 414 (3): 2602–2617, arXiv:1101.2406, Bibcode:2011MNRAS.414.2602D, doi:10.1111/j.1365-2966.2011.18575.x, S2CID 118560311.
^ De Bruijne, J. H. J.; Eilers, A.-C. (2012), "Radial velocities for the HIPPARCOS-Gaia Hundred-Thousand-Proper-Motion project", Astronomy & Astrophysics, 546: A61, arXiv:1208.3048, Bibcode:2012A&A...546A..61D, doi:10.1051/0004-6361/201219219, S2CID 59451347.
^ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ ^j ^k ^l ^m ⁿ Woodcock, K. (2021), "τ⁹ Eri: a bright pulsating magnetic Bp star in a 5.95-d double-lined spectroscopic binary", Monthly Notices of the Royal Astronomical Society, 502 (4): 5200–5209, arXiv:2101.11732, Bibcode:2021MNRAS.502.5200W, doi:10.1093/mnras/stab338
^ ^a ^b North, P. (June 1998), "Do SI stars undergo any rotational braking?", Astronomy and Astrophysics, 334: 181–187, arXiv:astro-ph/9802286, Bibcode:1998A&A...334..181N.
^ "tau09 Eri". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2016-10-13.{{cite web}}: CS1 maint: postscript (link)
^ ^a ^b Shulyak, D.; et al. (September 2014), "Interferometry of chemically peculiar stars: theoretical predictions versus modern observing facilities", Monthly Notices of the Royal Astronomical Society, 443 (2): 1629–1642, arXiv:1406.6093, Bibcode:2014MNRAS.443.1629S, doi:10.1093/mnras/stu1259.
^ Bychkov, V. D.; et al. (February 2005), "A catalog of stellar magnetic rotational phase curves", Astronomy and Astrophysics, 430 (3): 1143–1154, Bibcode:2005A&A...430.1143B, doi:10.1051/0004-6361:20034563.
^ ^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:1208.2037, Bibcode:2012MNRAS.427..343M, doi:10.1111/j.1365-2966.2012.21873.x, S2CID 118665352.
^ Abt, Helmut A.; et al. (July 2002), "Rotational Velocities of B Stars", The Astrophysical Journal, 573 (1): 359–365, Bibcode:2002ApJ...573..359A, doi:10.1086/340590.