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| Observation data Epoch J2000.0 Equinox J2000.0 | |
|---|---|
| Constellation | Hydra |
| Right ascension | 13h18m 55.29719s[1] |
| Declination | –23° 10′ 17.4514″[1] |
| Apparent magnitude (V) | +2.993[2] |
| Characteristics | |
| Spectral type | G8 III[3] |
| U−B color index | +0.645[2] |
| B−V color index | +0.920[2] |
| Astrometry | |
| Radial velocity (Rv) | –5.4[4] km/s |
| Proper motion (μ) | RA: +68.99[1] mas/yr Dec.: –41.85[1] mas/yr |
| Parallax (π) | 24.37 ± 0.15 mas[1] |
| Distance | 133.8 ± 0.8 ly (41.0 ± 0.3 pc) |
| Absolute magnitude (MV) | –0.15[3] |
| Details | |
| A | |
| Mass | 2.94[3] M☉ |
| Radius | 16±3[5] R☉ |
| Luminosity | 115[3] L☉ |
| Surface gravity (log g) | 3.02[6] cgs |
| Temperature | 5,087[6] K |
| Metallicity [Fe/H] | –0.06[6] dex |
| Rotational velocity (v sin i) | 8[7] km/s |
| Age | 372[3] Myr |
| B | |
| Mass | 0.61+0.12 −0.14[8] M☉ |
| Orbit[8] | |
| Primary | A |
| Companion | B |
| Semi-major axis (a) | 67.5±0.6or159±7 AU |
| Other designations | |
46 Hydrae, BD–22 3554, FK5 495, HD 115659, HIP 64962, HR 5020, NSV 6180, SAO 181543.[9] | |
| Database references | |
| SIMBAD | data |
Gamma Hydrae (γ Hya, γ Hydrae) is a binary star in the equatorial constellationofHydra. It has an apparent visual magnitude of 3.0,[2] placing it second in brightness among the members of this generally faint constellation. Based upon parallax measurements made during the Hipparcos mission, this star is at a distance of around 133.8 light-years (41.0 parsecs) from Earth.[1]
The stellar spectrum of the primary matches a stellar classification of G8 III,[3] with the luminosity class of III indicating it has evolved into a giant star after exhausting the supply of hydrogen at its core. It has nearly three[3] times the mass of the Sun and 16 times the Sun's radius.[5] The star is radiating 115[3] times the Sun's luminosity from its outer atmosphere at an effective temperature of 5,019 K.[3] This heat gives it the yellow glow of a K-type star.[10] Despite having reached an advanced stage in its evolution, it is considerably younger than the Sun with an age of around 372 million years. This is because higher mass stars consume their nuclear fuel at a more rapid rate.[3]
The secondary component component, named Gamma Hydrae B, shares a common proper motion with the primary star. Radial velocity observations confirmed it to be physically bound to Gamma Hydrae A. It has around 60% the mass of the Sun and is located at 1.6" from the primary. The physical separation is either 67.5 or 159 astronomical units.[8]
γ Hya appears on the flag of Brazil, symbolising the state of Acre.[11]
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