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    Tau4 Eridani

    Topic: Astronomy

     From Handwiki - Reading time: 4 min
    Short description: Binary star system in the constellation Eridanus


    τ4 Eridani
    Eridanus constellation map.svg
    Red circle.svg
    Location of τ4 Eridani (circled)
    Observation data
    Epoch J2000.0   Equinox (celestial coordinates)
    Constellation Eridanus
    Right ascension  03h 19m 31.00224s[1]
    Declination −21° 45′ 28.3049″[1]
    Apparent magnitude (V) 3.65[2]
    Characteristics
    Evolutionary stage asymptotic giant branch[3]
    Spectral type M3/4 III[4]
    U−B color index +1.79[2]
    B−V color index +1.61[2]
    Variable type Lb[5]
    Astrometry
    Radial velocity (Rv)+41.7±0.7[6] km/s
    Proper motion (μ) RA: +51.89[1] mas/yr
    Dec.: +32.92[1] mas/yr
    Parallax (π)10.6153 ± 0.3213[7] mas
    Distance307 ± 9 ly
    (94 ± 3 pc)
    Absolute magnitude (MV)−0.79[8]
    Details
    Mass1.8±0.3[9] M☉
    Radius106[10] R☉
    Luminosity1,537[11] L☉
    Temperature3,712[9] K
    Other designations
    τ4 Eridani, τ4 Eri, 16 Eridani, BD-22° 584, HD 20720, HIP 15474, HR 1003, SAO 168460.[12]
    Database references
    SIMBADdata

    Tau4 Eridani (τ4 Eridani, τ4 Eri) is a binary star system in the constellation Eridanus. It is visible to the naked eye with an apparent visual magnitude of 3.65.[2] The distance to this star can be estimated using the parallax method, which yields a value of roughly 300 light years.[1]

    A visual band light curve for Tau4 Eridani, plotted from data published by Tabur et al. (2009)[13]

    This is an evolved red giant star currently on the asymptotic giant branch[3] with a stellar classification of M3/4 III.[4] It is a slow irregular variable star of type Lb, undergoing changes in magnitude over the range 3.57−3.72[5] with a periodicity of 23.8 d.[13] The measured angular diameter of Tau4 Eridani is 10.58±1.00 mas.[14] At its estimated distance, this yields a physical size of about 106 times the radius of the Sun.[10] It shines with 1,537[11] times the luminosity of the Sun from an outer atmosphere at an effective temperature of 3,712 K.[9]

    This is most likely a binary star system.[15] The companion is a magnitude 9.5 star at an angular separation of 5.7″ along a position angle of 291°, as of 2013.[16]

    References

    1. ↑ 1.0 1.1 1.2 1.3 1.4 van Leeuwen, F. (2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics 474 (2): 653–664, doi:10.1051/0004-6361:20078357, Bibcode: 2007A&A...474..653V. 
    2. ↑ 2.0 2.1 2.2 2.3 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. ↑ 3.0 3.1 Lebzelter, T.; Hron, J. (January 2008), "BRITE stars on the AGB", Communications in Asteroseismology 152: 178–181, doi:10.1553/cia152s178, Bibcode: 2008CoAst.152..178L, https://hw.oeaw.ac.at/0xc1aa5576_0x0019d7d9.pdf. 
    4. ↑ 4.0 4.1 Houk, N.; Smith-Moore, M. (1988), Michigan Catalogue of Two-dimensional Spectral Types for the HD Stars, 4, Bibcode: 1988mcts.book.....H. 
    5. ↑ 5.0 5.1 Ruban, E. V. et al. (September 2006), "Spectrophotometric observations of variable stars", Astronomy Letters 32 (9): 604–607, doi:10.1134/S1063773706090052, Bibcode: 2006AstL...32..604R. 
    6. ↑ Gontcharov, G. A. (November 2006), "Pulkovo Compilation of Radial Velocities for 35 495 Hipparcos stars in a common system", Astronomy Letters 32 (11): 759–771, doi:10.1134/S1063773706110065, Bibcode: 2006AstL...32..759G. 
    7. ↑ Brown, A. G. A. (2021). "Gaia Early Data Release 3: Summary of the contents and survey properties". Astronomy & Astrophysics 649: A1. doi:10.1051/0004-6361/202039657. Bibcode: 2021A&A...649A...1G.  Gaia EDR3 record for this source at VizieR.
    8. ↑ Cardini, D. (January 2005), "Mg II chromospheric radiative loss rates in cool active and quiet stars", Astronomy and Astrophysics 430: 303–311, doi:10.1051/0004-6361:20041440, Bibcode: 2005A&A...430..303C. 
    9. ↑ 9.0 9.1 9.2 Halabi, Ghina M.; Eid, Mounib El (2015). "Exploring masses and CNO surface abundances of red giant stars". Monthly Notices of the Royal Astronomical Society 451 (3): 2957. doi:10.1093/mnras/stv1141. Bibcode: 2015MNRAS.451.2957H. 
    10. ↑ 10.0 10.1 Lang, Kenneth R. (2006), Astrophysical formulae, Astronomy and astrophysics library, 1 (3 ed.), Birkhäuser, ISBN 3-540-29692-1, https://books.google.com/books?id=OvTjLcQ4MCQC&pg=PA41.  The radius (R*) is given by:
      [math]\displaystyle{ \begin{align} 2\cdot R_* & = \frac{(93\cdot 10.58\cdot 10^{-3})\ \text{AU}}{0.0046491\ \text{AU}/R_{\bigodot}} \\ & \approx 212\cdot R_{\bigodot} \end{align} }[/math]
    11. ↑ 11.0 11.1 McDonald, I. et al. (2012), "Fundamental Parameters and Infrared Excesses of Hipparcos Stars", Monthly Notices of the Royal Astronomical Society 427 (1): 343–57, doi:10.1111/j.1365-2966.2012.21873.x, Bibcode: 2012MNRAS.427..343M. 
    12. ↑ "tau04 Eri". SIMBAD. Centre de données astronomiques de Strasbourg. http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=tau04+Eri. 
    13. ↑ 13.0 13.1 Tabur, V. et al. (December 2009), "Long-term photometry and periods for 261 nearby pulsating M giants", Monthly Notices of the Royal Astronomical Society 400 (4): 1945–1961, doi:10.1111/j.1365-2966.2009.15588.x, Bibcode: 2009MNRAS.400.1945T. 
    14. ↑ Richichi, A.; Percheron, I. (May 2005), "First results from the ESO VLTI calibrators program", Astronomy and Astrophysics 434 (3): 1201–1209, doi:10.1051/0004-6361:20042257, Bibcode: 2005A&A...434.1201R. 
    15. ↑ 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, doi:10.1111/j.1365-2966.2008.13596.x, Bibcode: 2008MNRAS.389..869E. 
    16. ↑ Mason, B. D. et al. (2014), "The Washington Visual Double Star Catalog", The Astronomical Journal 122 (6): 3466–3471, doi:10.1086/323920, Bibcode: 2001AJ....122.3466M, http://vizier.u-strasbg.fr/viz-bin/VizieR?-source=B/wds, retrieved 2015-07-22 



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