Phi Eridani

φ Eridani (Latinised as Phi Eridani) is a star in the constellation Eridanus. It is visible to the naked eye with an apparent visual magnitude of 3.55.[2] The distance to this star, as determined using the parallax method, is around 154 light years.[1]

φ Eridani
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Eridanus
Right ascension  02h 16m 30.58563s[1]
Declination −51° 30′ 43.7955″[1]
Apparent magnitude (V) 3.55[2]
Characteristics
Spectral type B8IV-V[3]
U−B color index −0.38[2]
B−V color index −0.12[2]
Astrometry
Radial velocity (Rv)10.40[4] km/s
Proper motion (μ) RA: +91.03[1] mas/yr
Dec.: −22.23[1] mas/yr
Parallax (π)21.22 ± 0.12[1] mas
Distance153.7 ± 0.9 ly
(47.1 ± 0.3 pc)
Absolute magnitude (MV)0.183±0.027[5]
Details
Mass3.55[6] M☉
Radius3.4[7] R☉
Luminosity255[8] L☉
Surface gravity (log g)4.21±0.14[6] cgs
Temperature13,716±466[6] K
Rotational velocity (v sin i)250[9] km/s
Age44[6] Myr
Other designations
φ Eri, CPD−52° 285, FK5 82, HD 14228, HIP 10602, HR 674, SAO 232696.[10]
Database references
SIMBADdata

This is a B-type star with a stellar classification of B8IV-V,[3] suggesting it shows traits of a main sequence star and a subgiant. It is spinning rapidly with a projected rotational velocity of 250 km/s. This rotation is giving the star an oblate shape with an equator that is 17% larger than the polar radius. The estimated angular size is 0.68 milliarcseconds.[9] Since the distance is known, this yields a physical size of around 3.4 times the radius of the Sun.[7] It has 3.55 times the mass of the Sun and radiates 255 times the solar luminosity from its outer atmosphere at an effective temperature of about 13,716 K.[6]

Phi Eridani may form a wide binary star system with a 9th magnitude star at lies an angular separation of 86″. This companion is a G-type main sequence star with a stellar classification of G2V.[11] It may also have a physical association with the naked-eye star Eta Horologii.[12] It is a member of the Tucana-Horologium association, a 45 ± 4 Myr old group of stars that share a common motion through space.[5]

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 Mermilliod, J.-C. (1986), "Compilation of Eggen's UBV data, transformed to UBV (unpublished)", Catalogue of Eggen's UBV Data, SIMBAD, Bibcode:1986EgUBV........0M.
  3. Zuckerman, B.; Song, Inseok (2004), "Young Stars Near the Sun", Annual Review of Astronomy & Astrophysics, 42 (1): 685–721, Bibcode:2004ARA&A..42..685Z, doi:10.1146/annurev.astro.42.053102.134111.
  4. 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.
  5. Bell, Cameron P. M.; et al. (November 2015), "A self-consistent, absolute isochronal age scale for young moving groups in the solar neighbourhood", Monthly Notices of the Royal Astronomical Society, 454 (1): 593–614, arXiv:1508.05955, Bibcode:2015MNRAS.454..593B, doi:10.1093/mnras/stv1981.
  6. 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.
  7. Lang, Kenneth R. (2006), Astrophysical formulae, Astronomy and astrophysics library, 1 (3rd ed.), Birkhäuser, ISBN 3-540-29692-1. The radius (R*) is given by:
  8. 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.
  9. van Belle, Gerard T. (March 2012), "Interferometric observations of rapidly rotating stars", The Astronomy and Astrophysics Review, 20 (1): 51, arXiv:1204.2572, Bibcode:2012A&ARv..20...51V, doi:10.1007/s00159-012-0051-2.
  10. "phi Eri". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2016-10-13.
  11. 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.
  12. Shaya, Ed J.; Olling, Rob P. (January 2011), "Very Wide Binaries and Other Comoving Stellar Companions: A Bayesian Analysis of the Hipparcos Catalogue", The Astrophysical Journal Supplement, 192 (1): 2, arXiv:1007.0425, Bibcode:2011ApJS..192....2S, doi:10.1088/0067-0049/192/1/2.
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