Tau Sagittarii

Tau Sagittarii (Tau Sgr, τ Sagittarii, τ Sgr) is a star in the southern zodiac constellation of Sagittarius.

Description

With an apparent visual magnitude of +3.3, this is one of the brighter members of the constellation. The distance of this star from Earth is roughly 122 light-years (37 parsecs), based upon parallax measurements.

This is a spectral type K1 giant star with about 1.25 M_☉. The stellar envelope is slightly cooler than the Sun with an effective temperature of 4,459 K, giving the star a light orange color. The interferometry-measured angular diameter of this star, after correcting for limb darkening, is 3.93 ± 0.04 mas, which, at its estimated distance, equates to a physical radius of about 16 times the radius of the Sun.

τ Sagittarii is a suspected double star although no companion has been confirmed yet. A lower metal content (Fe to H ratio is 54% lower than the sun's) and a high peculiar velocity (64 km/s, four times the local average) relative to the Sun suggest the star is a visitor from a different part of the Galaxy.

τ  Sagittarii is a red clump giant, a star with a similar mass to the sun which has exhausted its core hydrogen, passed through the red giant branch, and started helium fusion in its core.

The Wow! signal

τ Sagittarii is the closest constellational star (a star that is part of the traditional outline of a constellation) to the origin of the 1977 Wow! signal.

Name and etymology

• The star forms part of simple asterisms:
  • γ Sgr, τ Sgr, δ Sgr, ε Sgr, ζ Sgr, λ Sgr, σ Sgr and φ Sgr — the Teapot.
  • φ Sgr, τ Sgr, ζ Sgr, χ Sgr (double) and σ Sgr — the Returning Ostriches; in Arabic Al Naʽām al Ṣādirah often transliterated as Namalsadirah (النعم السادرة).
    • Originally four stars in a numerical order: φ Sgr, τ Sgr, χ¹ Sgr and χ² Sgr
  • ν Sgr, τ Sgr, ψ Sgr, ω Sgr, 60 Sgr and ζ Sgr, Al Udḥiyy — the Ostrich's Nest.
  • In the entirely separate Chinese tradition — 斗 (Dǒu), meaning Dipper: τ Sgr, φ Sgr, λ Sgr, μ Sgr, σ Sgr and ζ Sgr. The star itself is 斗宿五 (Dǒu Xiù wǔ, English: the Dipper's fifth star).

References

1. Sigma Sagittarii
2. Epsilon Sagittarii
3. Zeta Sagittarii
4. Wow! signal
5. Sagittarius (constellation)
6. Lambda Sagittarii
7. List of brightest natural objects in the sky
8. Delta Sagittarii
9. Gamma2 Sagittarii
10. Nu1 Sagittarii
11. Mu Sagittarii
12. HR 7703
13. UX Tauri
14. IAU designated constellations
15. List of Arabic star names
16. Occultation
17. List of nearest stars
18. List of stars for navigation
19. O-type star
20. List of largest stars