τ9 Eridani

A light curve for Tau9 Eridani plotted from TESS data[1]
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Eridanus
Right ascension 03h 59m 55.48381s[2]
Declination −24° 00′ 58.3798″[2]
Apparent magnitude (V) 4.63[3]
Characteristics
Spectral type B9.5V Si[4]
U−B color index −0.40[3]
B−V color index −0.13[3]
Variable type α2 CVn[5]
Astrometry
Radial velocity (Rv)25.5±0.5[6] km/s
Proper motion (μ) RA: +12.12[2] mas/yr
Dec.: +16.48[2] mas/yr
Parallax (π)9.96 ± 0.22 mas[2]
Distance327 ± 7 ly
(100 ± 2 pc)
Absolute magnitude (MV)−0.44[5]
Orbit[7]
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
Mass3.6[7] M☉
Radius3.06[7] R☉
Luminosity209[7] L☉
Surface gravity (log g)4.11±0.11[8] cgs
Temperature12,580[7] K
Rotational velocity (v sin i)26.8[7] km/s
Age140[7] Myr
τ9 Eri B
Mass1.6[7] M☉
Radius1.5[7] R☉
Luminosity6.3[7] L☉
Temperature7530[7] K
Rotational velocity (v sin i)15[7] km/s
Other designations
τ9 Eridani, τ9 Eri, 36 Eridani, CD−24° 2022, FK5 2287, HD 25267, HIP 18673, HR 1240, SAO 169017.[9]
Database references
SIMBADdata

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

  1. ↑ "MAST: Barbara A. Mikulski Archive for Space Telescopes". Space Telescope Science Institute. Retrieved 8 December 2021.
  2. 1 2 3 4 5 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.
  3. 1 2 3 4 5 Mermilliod, J.-C. (1986), "Compilation of Eggen's UBV data, transformed to UBV (unpublished)", Catalogue of Eggen's UBV Data, SIMBAD, Bibcode:1986EgUBV........0M.
  4. 1 2 3 4 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.
  5. 1 2 3 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.
  6. ↑ 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.
  7. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 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
  8. 1 2 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.
  9. ↑ "tau09 Eri". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2016-10-13.{{cite web}}: CS1 maint: postscript (link)
  10. 1 2 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.
  11. ↑ 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.
  12. 1 2 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.
  13. ↑ 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.
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