Tau1_Hydrae
Tau1 Hydrae
Triple star system in the constellation Hydra
Tau1 Hydrae is a triple star[3] system in the equatorial constellation of Hydra. Based upon the annual parallax shift of the two visible components as seen from Earth,[1] they are located about 18 parsecs (59 ly) from the Sun. The system has a combined apparent visual magnitude of +4.59,[2] which is bright enough to be visible to the naked eye at night.
The inner pair of stars form a single-lined spectroscopic binary with an orbital period of about 2,807 days and an eccentricity of 0.33.[8] The visible member of the pair, component A, is a visual magnitude 4.60[2] F-type main sequence star with a stellar classification of F6 V.[3] During the 1990s, it was thought to be a Gamma Doradus variable, but this was later discounted as it shows no short-term photometric variability. The star does show some long-term variability, possibly as a result of a magnetic activity cycle similar to the solar cycle.[13]
The tertiary member, component B, is a visual magnitude 7.15[2] K-type star with a class of K0.[3] It lies at a separation of 1,120 AU from the primary.[14] As of 2012, it was positioned at an angular separation of 67.5 arc seconds along a position angle of 4°.[15]