27 Hydrae
27 Hydrae is a triple star system system in the equatorial constellation of Hydra, located 222 light years away from the Sun. It is visible to the naked eye as a faint, orange-hued star with a combined apparent visual magnitude of 4.82. The system is moving further from the Earth with a heliocentric radial velocity of +25.6 km/s.
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Hydra |
| Right ascension | 09h 20m 29.01857s |
| Declination | −09° 33′ 20.5054″ |
| Apparent magnitude (V) | 4.818 (4.91 + 7.03 + 10.99) |
| Characteristics | |
| Spectral type | K0III + F4V + K2V |
| Astrometry | |
| Radial velocity (Rv) | +25.60±0.13 km/s |
| Proper motion (μ) | RA: −12.48 mas/yr Dec.: −27.37 mas/yr |
| Parallax (π) | 14.66 ± 0.31 mas |
| Distance | 222 ± 5 ly (68 ± 1 pc) |
| Details | |
| A | |
| Mass | 2.17 M☉ |
| Radius | 11 R☉ |
| Luminosity | 57.5 L☉ |
| Surface gravity (log g) | 2.9 cgs |
| Temperature | 4,965±26 K |
| Metallicity [Fe/H] | −0.07 dex |
| Rotational velocity (v sin i) | 3.3 km/s |
| Age | 1.91 Gyr |
| B | |
| Radius | 1.82 R☉ |
| Luminosity | 5.885 L☉ |
| Temperature | 6,664 K |
| C | |
| Radius | 0.72 R☉ |
| Luminosity | 0.227 L☉ |
| Temperature | 4,685 K |
| Other designations | |
| A: 27 Hya, BD−08°2643, HD 80586, HIP 45811, HR 3709, SAO 136768 | |
| B: BD−09°2801, HD 80550, HIP 45802, SAO 136767 | |
| C: TYC 5463-1518-1 | |
| Database references | |
| SIMBAD | data |
| B | |
| C | |
The magnitude 4.91 primary, component A, is an aging giant star with a stellar classification of K0 III. It is a red clump giant, which indicates it is on the horizontal branch and is generating energy through helium fusion at its core. The star is 1.9 billion years old with 2.17 times the mass of the Sun. It has swelled to 11 times the Sun's radius and is radiating 57.5 times the Sun's luminosity from its enlarged photosphere at an effective temperature of 4,965 K. The star is suspected to host a low-mass companion.
The stellar companions to this star, designated components B and C, lie at an angular separation of 229.10″ from the primary, and form a binary pair with a separation of 9.20″ as of 2015. The brighter member of the pair, component B, is a seventh magnitude F-type main-sequence star with a class of F4 V, while its companion is an eleventh magnitude K-type main-sequence star with a class of K2 V.