HU Delphini
Star in the constellation Delphinus
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HU Delphini, also known as Gliese 791.2, is a star system in the constellation of Delphinus. 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.
A visual band light curve for HU Delphini, plotted from ASAS-SN data.[1] The main plot shows the long-term variability, and the inset plot shows the periodic variability. | |
| Observation data Epoch J2000 Equinox ICRS | |
|---|---|
| Constellation | Delphinus |
| Right ascension | 20h 29m 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[7] | |
| Period (P) | 1.47080±0.00031 yr |
| Semi-major axis (a) | 0.0971±0.0006″ |
| Eccentricity (e) | 0.6232±0.0059 |
| Inclination (i) | 162±3° |
| Longitude of the node (Ω) | 282±2° |
| Periastron epoch (T) | 2019.1567±0.0033 |
| Argument of periastron (ω) (secondary) | 9.6±2.3° |
| Semi-amplitude (K1) (primary) | 5.66±0.61 km/s |
| Semi-amplitude (K2) (secondary) | 11.15±0.63 km/s |
| Details[3] | |
| HU Del A | |
| Mass | 0.237 ± 0.004 M☉ |
| Metallicity [Fe/H] | 0.07 dex |
| Rotation | 0.3085±0.0005[8] days |
| Rotational velocity (v sin i) | 35.1±0.2[8] 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 1.47080 years and a somewhat high eccentricity of 0.6232. The orbit has been determined from imaging and radial velocity.[7]
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.[8] While the normal surface temperature of the primary is 3000 K, the starspots themselves are slightly cooler, at about 2700 K. It is also a flare star,[4] the first flare been detected in August 2000.[9] The secondary star has a mass of 11.4% that of the Sun.[3]