42 Herculis
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Hercules |
| Right ascension | 16h 38m 44.84465s |
| Declination | +48° 55′ 42.0160″ |
| Apparent magnitude (V) | 4.86 |
| Characteristics | |
| Evolutionary stage | asymptotic giant branch |
| Spectral type | M2.5III |
| B−V color index | 1.562±0.011 |
| Astrometry | |
| Radial velocity (Rv) | −55.74±0.33 km/s |
| Proper motion (μ) | RA: −47.768 mas/yr Dec.: +27.349 mas/yr |
| Parallax (π) | 7.2737±0.1764 mas |
| Distance | 450 ± 10 ly (137 ± 3 pc) |
| Absolute magnitude (MV) | −0.65 |
| Details | |
| Radius | 63.81+5.20 −7.75 R☉ |
| Luminosity | 733.6±20.5 L☉ |
| Surface gravity (log g) | 1.50 cgs |
| Temperature | 3,760.5+251.5 −144.5 K |
| Other designations | |
| 42 Her, NSV 7896, AAVSO 1636+49, BD+49°2531, FK5 1434, HD 150450, HIP 81497, HR 6200, SAO 46210, WDS J16387+4856 | |
| Database references | |
| SIMBAD | data |
42 Herculis is a single star located around 450 light years away from the Sun in the northern constellation of Hercules. It is visible to the naked eye as a faint, red-hued star with an apparent visual magnitude of 4.86. The star is moving closer to the Earth with a heliocentric radial velocity of −56 km/s.
This is an aging red giant star on the asymptotic giant branch with a stellar classification of M2.5III. It has been catalogued as a suspected variable star, although a 1992 photometric survey found the brightness to be constant. Having exhausted the supply of hydrogen at its core, the star has expanded to 64 times the Sun's radius. It is radiating 734 times the luminosity of the Sun from its swollen photosphere at an effective temperature of 3761 K.
There is an unknown source of X-ray and far ultraviolet emission originating from a location offset by more than one arcsecond from the star. This may indicate there is an undetected main sequence companion.