89 Herculis
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Hercules |
| Right ascension | 17h 55m 25.18845s |
| Declination | +26° 02′ 59.9701″ |
| Apparent magnitude (V) | (5.34 - 5.54) |
| Characteristics | |
| Evolutionary stage | post-AGB |
| Spectral type | F2Ibe |
| U−B color index | −0.34 |
| B−V color index | +0.34 |
| Variable type | SRd |
| Astrometry | |
| Radial velocity (Rv) | −28.5 km/s |
| Proper motion (μ) | RA: 3.894 mas/yr Dec.: 5.193 mas/yr |
| Parallax (π) | 0.6893±0.0718 mas |
| Distance | approx. 4,700 ly (approx. 1,500 pc) |
| Absolute magnitude (MV) | −6.5 |
| Orbit | |
| Period (P) | 288.36 days |
| Eccentricity (e) | 0.189 |
| Semi-amplitude (K1) (primary) | 3.09 km/s |
| Details | |
| 89 Her A | |
| Mass | 1.0 M☉ |
| Radius | 71.0 R☉ |
| Luminosity | 8,350 L☉ |
| Surface gravity (log g) | 0.55 cgs |
| Temperature | 6,550 K |
| Metallicity | −0.5 |
| Rotational velocity (v sin i) | 23 km/s |
| Other designations | |
| 89 Her, V441 Herculis, AAVSO 1751+26, BD+26°3120, FK5 1468, GC 24382, HD 163506, HIP 87747, HR 6685, SAO 85545 | |
| Database references | |
| SIMBAD | data |
89 Herculis is a binary star system located about 4,700 light years away from the Sun in the northern constellation of Hercules. It is visible to the naked eye as a faint, fifth magnitude star. The system is moving closer to the Earth with a heliocentric radial velocity of −28.5 km/s.
This is a spectroscopic binary with the pair surrounded by a dusty disc, and an hourglass-shaped nebula formed from outflowing gas. The mass of the nebula is about 0.018 M☉, of which a majority is in the outflow. The system shows variable brightness and spectral line profiles. The companion has a very low mass and luminosity and orbits the primary in 288 days.
The primary component has a stellar classification of F2Ibe, and is among a rare class of post-asymptotic giant branch stars – low-mass stars in the last stages of their lives, highly inflated to appear as supergiants. It is classified as a semiregular variable star, subtype SRd, and ranges from magnitude 5.3 down to 5.5 over a period of around 68 days. The star has expanded to 71 times the Sun's radius and is radiating 8,350 times the Sun's luminosity from its enlarged photosphere at an effective temperature of 6,550 K.