26 Hydrae
Binary star system in the constellation Hydra
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26 Hydrae is a binary star[3] system located 334 light years away from the Sun in the equatorial constellation of Hydra. It is visible to the naked eye as a faint, yellow-hued point of light with a combined apparent visual magnitude of 4.77,[2] just a few degrees away from Alphard. The system is moving closer to the Earth with a leisurely radial velocity of -1 km/s.[9]
 | |
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Hydra |
| Right ascension | 09h 19m 46.38309s[1] |
| Declination | −11° 58′ 29.4577″[1] |
| Apparent magnitude (V) | 4.770[2] + 12.4[3] |
| Characteristics | |
| Evolutionary stage | red clump[4] |
| Spectral type | G7III[5] or G8II[6] |
| U−B color index | +0.67[7] |
| B−V color index | +0.927±0.017[8] |
| Astrometry | |
| Radial velocity (Rv) | −1.18±0.09[9] km/s |
| Proper motion (μ) | RA: −29.269[1] mas/yr Dec.: +11.613[1] mas/yr |
| Parallax (π) | 9.7770±0.1610 mas[1] |
| Distance | 334 ± 5 ly (102 ± 2 pc) |
| Absolute magnitude (MV) | −0.29[8] |
| Details | |
| 26 Hya A | |
| Mass | 2.72[10] M☉ |
| Radius | 15.14+0.81 −2.47[1] R☉ |
| Luminosity | 138.5±2.7[1] L☉ |
| Surface gravity (log g) | 2.48±0.07[11] cgs |
| Temperature | 5,003±82[10] K |
| Metallicity [Fe/H] | −0.13±0.06[11] dex |
| Rotational velocity (v sin i) | 2.7[9] km/s |
| Age | 0.51[10] Gyr |
| Other designations | |
| 26 Hya, BD−11°2609, FK5 2741, HD 80499, HIP 45751, HR 3706, SAO 155096, WDS J09198-1158AB[12] | |
| Database references | |
| SIMBAD | data |
Keenan and McNeil (1989) gave the brighter component a stellar classification of G7 III,[5] matching an aging giant star. Houk and Swift (1999) have it classed as a G8II[6] bright giant. This is a red clump giant,[4] which indicates it is on the horizontal branch and is generating energy through helium fusion at its core. It has a high lithium abundance and displays a far infrared emission excess.[13] The star is an estimated 510[10] million years old with 2.72[10] times the mass of the Sun and has expanded to 15[1] times the Sun's radius. It is radiating 139[1] times the luminosity of the Sun from its swollen photosphere at an effective temperature of 5,003 K.[10]
The secondary component is a magnitude 12.4 star at an angular separation of 3.2″, as of 2008.[3]