99 Herculis
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Hercules |
| Right ascension | 18h 07m 01.53971s |
| Declination | +30° 33′ 43.6896″ |
| Apparent magnitude (V) | 5.066 (A: 5.10; B: 8.45) |
| Characteristics | |
| Spectral type | F7 V + K4 V |
| U−B color index | –0.056 |
| B−V color index | +0.548 |
| Astrometry | |
| Radial velocity (Rv) | +1.7 km/s |
| Proper motion (μ) | RA: −100.32 mas/yr Dec.: +110.08 mas/yr |
| Parallax (π) | 63.93±0.34 mas |
| Distance | 51.0 ± 0.3 ly (15.64 ± 0.08 pc) |
| Absolute magnitude (MV) | 4.08 |
| Orbit | |
| Period (P) | 56.3±0.1 yr |
| Semi-major axis (a) | 1.06±0.02″ |
| Eccentricity (e) | 0.766±0.004 |
| Inclination (i) | 39±2° |
| Longitude of the node (Ω) | 41±2° |
| Periastron epoch (T) | 1997.62±0.05 |
| Argument of periastron (ω) (secondary) | 116±2° |
| Details | |
| 99 Her A | |
| Mass | 1.14 M☉ |
| Radius | 1.34 R☉ |
| Luminosity | 1.90 L☉ |
| Surface gravity (log g) | 4.17 cgs |
| Temperature | 5,908 K |
| Metallicity [Fe/H] | –0.60 dex |
| Rotational velocity (v sin i) | 5 km/s |
| Age | 9.37 Gyr |
| 99 Her B | |
| Mass | 0.46 M☉ |
| Radius | 0.67 R☉ |
| Luminosity | 0.19 L☉ |
| Temperature | 4,449 K |
| Other designations | |
| b Her, 99 Her, BD+30°3128, GJ 704, HD 165908, HIP 88745, HR 6775, SAO 66648 | |
| Database references | |
| SIMBAD | A |
| B | |
99 Herculis is the Flamsteed designation for a binary star system in the northern constellation of Hercules. It has the Bayer designation b Herculis, while 99 Herculis is the Flamsteed designation. This system has an apparent visual magnitude of 5.1, which, according to the Bortle scale, makes it faintly visible to the naked eye from suburban skies. Measurements made with the Hipparcos spacecraft show an annual parallax shift of 0.064″, corresponding to a physical distance of about 51.0 ly (15.6 pc) from the Sun. The system is moving further from the Earth with a heliocentric radial velocity of +1.7 km/s.
The binary nature of this star system was first discovered in 1859 by English astronomer W. R. Dawes. The two stellar components orbit around their common center of mass, or barycenter, with a period of 56.3 years and an eccentricity of 0.766. The semi-major axis of their orbit spans an angle of 1.06 arcseconds, which corresponds to a physical dimension of 16.5 AU. The plane of their orbit is inclined by an angle of about 39° to the line-of-sight from the Earth. Reports of a third component of this system now appear doubtful.