Binary star system in the constellation Aries
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! style="text-align: center; background-color: #FFFFC0;" colspan="2" | Observation dataEpoch J2000      Equinox J2000
! style="text-align:left" | Constellation
! style="text-align:left" | Right ascension
! style="text-align:left" | Declination
! style="text-align:left" | Apparent magnitude (V)
! style="background-color: #FFFFC0; text-align: center;" colspan="2"| Characteristics
! style="text-align:left" | Spectral type
! style="text-align:left" | U−B 
! style="text-align:left" | B−V 
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Tau1 Arietis, Latinized from τ1 Arietis, is the Bayer designation for a triple star system in the northern constellation of Aries. Based upon an annual parallax shift of , it is approximately distant from Earth. The combined apparent visual magnitude is 5.27, making it faintly visible to the naked eye.
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. Its period is 2.20356 days. The third component is located at an angular separation of 0.810 arcseconds and has a magnitude of 8.17. The primary component is a subgiant star with a stellar classification of B5 IV. It has five times the mass of the Sun with about four times the Sun's radius.
This system is a member of the Cas-Tau OB association of stars that share a common motion through space.
References.
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