89 Herculis
Star in the constellation Hercules
From Wikipedia, the free encyclopedia
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.[5]
 | |
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Hercules |
| Right ascension | 17h 55m 25.18845s[1] |
| Declination | +26° 02′ 59.9701″[1] |
| Apparent magnitude (V) | 5.34 - 5.54[2] |
| Characteristics | |
| Evolutionary stage | post-AGB[3] |
| Spectral type | F2Ibe[3] |
| U−B color index | −0.34[4] |
| B−V color index | +0.34[4] |
| Variable type | SRd[2] |
| Astrometry | |
| Radial velocity (Rv) | −28.5[5] km/s |
| Proper motion (μ) | RA: 3.894[1] mas/yr Dec.: 5.193[1] mas/yr |
| Parallax (π) | 0.6893±0.0718 mas[1] |
| Distance | approx. 4,700 ly (approx. 1,500 pc) |
| Absolute magnitude (MV) | −6.5[6] |
| Orbit[7] | |
| Period (P) | 288.36 days |
| Eccentricity (e) | 0.189 |
| Semi-amplitude (K1) (primary) | 3.09 km/s |
| Details | |
| 89 Her A | |
| Mass | 1.0[8] M☉ |
| Radius | 71.0[8] R☉ |
| Luminosity | 8,350[8] L☉ |
| Surface gravity (log g) | 0.55[3] cgs |
| Temperature | 6,550[3] K |
| Metallicity | −0.5[3] |
| Rotational velocity (v sin i) | 23[9] 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[10] | |
| Database references | |
| SIMBAD | data |
This is a spectroscopic binary with the pair surrounded by a dusty disc, and an hourglass-shaped nebula formed from outflowing gas.[11] The mass of the nebula is about 0.018 M☉, of which a majority is in the outflow.[11] The system shows variable brightness and spectral line profiles.[12] The companion has a very low mass and luminosity and orbits the primary in 288 days.[3]
The primary component has a stellar classification of F2Ibe,[3] 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.[3] 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.[2] The star has expanded to 71[8] times the Sun's radius and is radiating 8,350[8] times the Sun's luminosity from its enlarged photosphere at an effective temperature of 6,550 K.[3]