HU Delphini, also known as Gliese 791.2, is a star system in the constellationofDelphinus. Its apparent magnitude is 13.07.[3] With a trigonometric parallax of 113.4 ± 0.2 mas,[3] it is about 28.76 light-years (8.82 parsecs) away from the Solar System.
| |
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Delphinus |
| Right ascension | 20h29m 48.344s[2] |
| Declination | +09° 41′ 20.25″[2] |
| Apparent magnitude (V) | 13.07[3] |
| Characteristics | |
| Spectral type | M4.5V[4] |
| U−B color index | +1.29[5] |
| B−V color index | +1.64[5] |
| Variable type | Flare star[6] |
| Astrometry | |
| Radial velocity (Rv) | -34.24 ± 0.07[3] km/s |
| Proper motion (μ) | RA: 673.1[3] mas/yr Dec.: 122.0[3] mas/yr |
| Parallax (π) | 113.4 ± 0.2 mas[3] |
| Distance | 28.76 ± 0.05 ly (8.82 ± 0.02 pc) |
| Absolute magnitude (MV) | 13.46 / 16.73[3] |
| Orbit[3] | |
| Period (P) | 538.6 ± 0.1 d |
| Semi-major axis (a) | 0.1037 ± 0.0005″ |
| Eccentricity (e) | 0.558 ± 0.005 |
| Inclination (i) | 145.4 ± 0.6° |
| Longitude of the node (Ω) | 102.2 ± 1.1° |
| Periastron epoch (T) | JD 2451022.7 ± 0.9 |
| Argument of periastron (ω) (secondary) | 12.2 ± 1.5° |
| Semi-amplitude (K1) (primary) | 4.09 ± 0.08 km/s |
| Semi-amplitude (K2) (secondary) | 8.54 ± 0.13 km/s |
| Details[3] | |
| HU Del A | |
| Mass | 0.237 ± 0.004 M☉ |
| Metallicity [Fe/H] | 0.07 dex |
| Rotation | 0.3085±0.0005[7] |
| Rotational velocity (v sin i) | 35.1±0.2[7] km/s |
| HU Del B | |
| Mass | 0.114 ± 0.002 M☉ |
| Other designations | |
HU Del, GJ 791.2, CCDM J20298+0941AB, LHS 3556, 2MASS J20294834+0941202, G 24-16[6] | |
| Database references | |
| SIMBAD | data |
| ARICNS | A |
| B | |
HU Delphini is a binary star with a well-defined period of 538.6 days. The orbit has been derived from astrometry as well as through spectral observations, although that has been difficult because of the high projected rotational velocity. It is also fairly eccentric, at 0.558.[3]
Both stars in the system are red dwarfs. The primary component of the system is only 23.7% as massive as the Sun,[3] so it is fully convective.[4] As a result, there are frequent starspots on its surface, especially near poles.[7] While the normal surface temperature of the primary is 3000 K, the starspots themselves are cooler: only 2700 K. It is also a flare star,[4] the first flare been detected in August 2000.[8] The secondary star has a mass of 11.4% that of the Sun.[3]
