Tau4 Eridani

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

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]

τ⁴ Eridani

Location of τ4 Eridani (circled)
Observation data Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation	Eridanus
Right ascension	03^h 19^m 31.00224^s^[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 mas^[7]
Distance	307 ± 9 ly (94 ± 3 pc)
Absolute magnitude (MV)	−0.79^[8]
Details
Mass	1.8±0.3^[9] M☉
Radius	106^[10] R☉
Luminosity	1,537^[11] L☉
Temperature	3,712^[9] K
Other designations
τ^4 Eridani, τ^4 Eri, 16 Eridani, BD-22° 584, HD 20720, HIP 15474, HR 1003, SAO 168460.^[12]
Database references
SIMBAD	data

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. 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.
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 Mermilliod, J.-C. (1986), "Compilation of Eggen's UBV data, transformed to UBV (unpublished)", Catalogue of Eggen's UBV Data, SIMBAD, Bibcode:1986EgUBV........0M.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. Lebzelter, T.; Hron, J. (January 2008), "BRITE stars on the AGB" (PDF), Communications in Asteroseismology, 152: 178–181, Bibcode:2008CoAst.152..178L, doi:10.1553/cia152s178.
4. Houk, N.; Smith-Moore, M. (1988), Michigan Catalogue of Two-dimensional Spectral Types for the HD Stars, vol. 4, Bibcode:1988mcts.book.....H.
5. Ruban, E. V.; et al. (September 2006), "Spectrophotometric observations of variable stars", Astronomy Letters, 32 (9): 604–607, Bibcode:2006AstL...32..604R, doi:10.1134/S1063773706090052, S2CID 121747360.
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, arXiv:1606.08053, Bibcode:2006AstL...32..759G, doi:10.1134/S1063773706110065, S2CID 119231169.
7. Brown, A. G. A.; et al. (Gaia collaboration) (2021). "Gaia Early Data Release 3: Summary of the contents and survey properties". Astronomy & Astrophysics. 649: A1. arXiv:2012.01533. Bibcode:2021A&A...649A...1G. doi:10.1051/0004-6361/202039657. S2CID 227254300. (Erratum: doi:10.1051/0004-6361/202039657e). 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, arXiv:astro-ph/0409683, Bibcode:2005A&A...430..303C, doi:10.1051/0004-6361:20041440, S2CID 12136256.
9. 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. arXiv:1507.01517. Bibcode:2015MNRAS.451.2957H. doi:10.1093/mnras/stv1141. S2CID 118707332.
10. Lang, Kenneth R. (2006), Astrophysical formulae, Astronomy and astrophysics library, vol. 1 (3 ed.), Birkhäuser, ISBN 3-540-29692-1. The radius (R_*) is given by:

    ${\displaystyle {\begin{aligned}2\cdot R_{*}&={\frac {(93\cdot 10.58\cdot 10^{-3})\ {\text{AU}}}{0.0046491\ {\text{AU}}/R_{\bigodot }}}\\&\approx 212\cdot R_{\bigodot }\end{aligned}}}$ 

11. 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.
12. "tau04 Eri". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2016-10-13.{{cite web}}: CS1 maint: postscript (link)
13. 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, arXiv:0908.3228, Bibcode:2009MNRAS.400.1945T, doi:10.1111/j.1365-2966.2009.15588.x, S2CID 15358380.
14. Richichi, A.; Percheron, I. (May 2005), "First results from the ESO VLTI calibrators program", Astronomy and Astrophysics, 434 (3): 1201–1209, arXiv:astro-ph/0501532, Bibcode:2005A&A...434.1201R, doi:10.1051/0004-6361:20042257, S2CID 2847613.
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, arXiv:0806.2878, Bibcode:2008MNRAS.389..869E, doi:10.1111/j.1365-2966.2008.13596.x, S2CID 14878976.
16. Mason, B. D.; et al. (2014), "The Washington Visual Double Star Catalog", The Astronomical Journal, 122 (6): 3466–3471, Bibcode:2001AJ....122.3466M, doi:10.1086/323920, retrieved 2015-07-22