Gamma Tauri (γ Tauri) is a solitary orange giant star located in the constellation Taurus. It is a member of the Hyades open cluster, the nearest rich star cluster to the Sun, and lies at an approximate distance of 153 light‑years (47 parsecs) from Earth.
Nomenclature and identifiers
- Bayer designation: γ Tauri
- Flamsteed designation: 73 Tauri
- Henry Draper Catalogue: HD 27371
- Hipparcos catalogue: HIP 20205
- Other catalogue numbers include SAO 93810, BD +14° 592, and HR 1362.
Astrophysical characteristics
- Spectral type: K0 III, indicating a K‑type giant star that has exhausted hydrogen in its core and expanded.
- Apparent magnitude: +3.65, making it visible to the naked eye under good conditions.
- Absolute magnitude: Approximately +0.5.
- Mass: About 2.7 M☉ (solar masses).
- Radius: Roughly 13 R☉ (solar radii).
- Luminosity: Approximately 100 L☉ (solar luminosities).
- Effective temperature: ~4,900 K, giving it a characteristic orange hue.
- Surface gravity (log g): ≈2.5 (cgs).
- Metallicity: Near solar ([Fe/H] ≈ 0.0), indicating a composition similar to the Sun.
- Radial velocity: +38 km s⁻¹, indicating motion away from the Solar System.
Membership in the Hyades
Gamma Tauri's proper motion and radial velocity are consistent with the Hyades cluster's space motion, confirming its status as a bona fide cluster member. Its position near the cluster’s outer region makes it a useful reference point for studies of the Hyades' age, distance, and stellar evolution.
Evolutionary status
As a K‑type giant, Gamma Tauri is in a post‑main‑sequence phase. Having left the main sequence after exhausting core hydrogen, it is now fusing hydrogen in a shell surrounding an inert helium core. The star is expected to eventually ignite helium in its core and evolve further along the red‑giant branch.
Historical and cultural notes
Gamma Tauri is sometimes referred to by the traditional name Prima Hyadum, meaning “the first Hyad” in Latin, reflecting its prominence among the Hyades stars. However, this name is less frequently used in modern astronomical literature.
Observational data
- Equatorial coordinates (J2000.0): Right ascension 03ʰ 47ᵐ 57.9ˢ, Declination +15° 38′ 47″.
- Parallax: 21.26 ± 0.33 mas (milliarcseconds), as measured by the Hipparcos mission, corroborated by Gaia DR3 data.
Gamma Tauri serves as a reference point for astrophysical studies of giant star atmospheres, cluster dynamics, and stellar evolutionary models due to its well‑determined parameters and cluster membership.
