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τ¹ Arietis
	Location of τ1 Arietis (circled)
Observation data; Epoch J2000 Equinox J2000
Constellation	Aries
Right ascension	03h 21m 13.62462s
Declination	+21° 08′ 49.4390″
Apparent magnitude (V)	5.27
Characteristics
Spectral type	B5 IV
U−B color index	−0.53
B−V color index	−0.06
Astrometry
Radial velocity (Rv)	+14 km/s
Proper motion (μ)	RA: +25.651 mas/yr ; Dec.: −19.850 mas/yr
Parallax (π)	6.1786 ± 0.2066 mas
Distance	530 ± 20 ly ; (162 ± 5 pc)
Absolute magnitude (MV)	−0.66
Details
Mass	5.0±0.1 M☉
Radius	4.45 R☉
Luminosity	234 L☉
Surface gravity (log g)	3.68 cgs
Temperature	12,606 K
Metallicity [Fe/H]	−0.63 dex
Rotational velocity (v sin i)	30 km/s
Age	54.8±5.4 Myr
Other designations
	τ1 Ari, 61 Arietis, BD+20 543, FK5 1094, HD 20756, HIP 15627, HR 1005, SAO 75886.
Database references
SIMBAD	data

Tau¹ Arietis, Latinized from τ¹ Arietis, is the Bayer designation for a triple star system^[9] in the northern constellation of Aries. Based upon an annual parallax shift of 6.1786 mas, it is approximately 530 light-years (162 parsecs) distant from Earth. The combined apparent visual magnitude is 5.27,^[2] making it faintly visible to the naked eye.

A light curve for Tau¹ Arietis, plotted from *TESS* data^[10]

The Tau¹ Arietis system contains three stars. The inner pair form an eclipsing binary system, with the brightness of the pair decreasing by 0.06 in magnitude during an eclipse of the primary.^[11] Its period is 2.20356 days.^[12] The third component is located at an angular separation of 0.810 arcseconds and has a magnitude of 8.17.^[9] The primary component is a subgiant star with a stellar classification of B5 IV.^[3] It has five times the mass of the Sun^[6] with about four times the Sun's radius.^[1]

This system is a member of the Cas-Tau OB association of stars that share a common motion through space.^[13]

References

^ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ ^j Vallenari, A.; et al. (Gaia collaboration) (2023). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy and Astrophysics. 674: A1. arXiv:2208.00211. Bibcode:2023A&A...674A...1G. doi:10.1051/0004-6361/202243940. S2CID 244398875. Gaia DR3 record for this source at VizieR.
^ ^a ^b ^c ^d Crawford, D. L.; Barnes, J. V.; Golson, J. C. (1971), "Four-color, H-beta, and UBV photometry for bright B-type stars in the northern hemisphere", The Astronomical Journal, 76: 1058, Bibcode:1971AJ.....76.1058C, doi:10.1086/111220.
^ ^a ^b Lesh, Janet Rountree (December 1968), "The Kinematics of the Gould Belt: an Expanding Group?", Astrophysical Journal Supplement, 17: 371, Bibcode:1968ApJS...17..371L, doi:10.1086/190179.
^ Evans, D. S. (June 20–24, 1966), "The Revision of the General Catalogue of Radial Velocities", in Batten, Alan Henry; Heard, John Frederick (eds.), Determination of Radial Velocities and their Applications, Proceedings from IAU Symposium no. 30, vol. 30, University of Toronto: International Astronomical Union, p. 57, Bibcode:1967IAUS...30...57E.
^ ^a ^b Anderson, E.; Francis, Ch. (2012), "XHIP: An extended hipparcos compilation", Astronomy Letters, 38 (5): 331, arXiv:1108.4971, Bibcode:2012AstL...38..331A, doi:10.1134/S1063773712050015, S2CID 119257644.
^ ^a ^b ^c Tetzlaff, N.; Neuhäuser, R.; Hohle, M. M. (January 2011), "A catalogue of young runaway Hipparcos stars within 3 kpc from the Sun", Monthly Notices of the Royal Astronomical Society, 410 (1): 190–200, arXiv:1007.4883, Bibcode:2011MNRAS.410..190T, doi:10.1111/j.1365-2966.2010.17434.x, S2CID 118629873.
^ Abt, Helmut A.; Levato, Hugo; Grosso, Monica (July 2002), "Rotational Velocities of B Stars", The Astrophysical Journal, 573 (1): 359–365, Bibcode:2002ApJ...573..359A, doi:10.1086/340590.
^ "tau01 Ari", SIMBAD, Centre de données astronomiques de Strasbourg, retrieved 2012-08-11.
^ ^a ^b 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.
^ MAST: Barbara A. Mikulski Archive for Space Telescopes, Space Telescope Science Institute, retrieved 8 December 2021.
^ Malkov, O. Yu.; et al. (February 2006), "A catalogue of eclipsing variables", Astronomy and Astrophysics, 446 (2): 785–789, Bibcode:2006A&A...446..785M, doi:10.1051/0004-6361:20053137, hdl:10995/73280.
^ "tau 1 Ari", The International Variable Star Index, AAVSO, retrieved 17 July 2022.
^ de Zeeuw, P. T.; et al. (January 1999), "A HIPPARCOS Census of the Nearby OB Associations", The Astronomical Journal, 117 (1): 354–399, arXiv:astro-ph/9809227, Bibcode:1999AJ....117..354D, doi:10.1086/300682, S2CID 16098861.