HU Aquarii
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Aquarius |
| Right ascension | 21h 07m 58.19445s |
| Declination | −05° 17′ 40.5577″ |
| Apparent magnitude (V) | +15.3 |
| Characteristics | |
| Spectral type | DAm / M4.5V |
| Variable type | AM Herculis |
| Astrometry | |
| Proper motion (μ) | RA: -64.579 mas/yr Dec.: -62.732 mas/yr |
| Parallax (π) | 5.2354±0.0457 mas |
| Distance | 623 ± 5 ly (191 ± 2 pc) |
| Orbit | |
| Period (P) | 2.08 hours |
| Semi-major axis (a) | 0.0032 au |
| Eccentricity (e) | 0.0 |
| Inclination (i) | 85° |
| Details | |
| Mass | 0.88/0.2 M☉ |
| Radius | 0.01/0.22 R☉ |
| Luminosity | 0.0022/0.0052 L☉ |
| Temperature | 12,500/3,400 K |
| Other designations | |
| HU Aqr, RBS 1724, RE J210755-051621, 1RXS J210758.5-051744, 1AXG J210759-0518, 2RE J210755-051630, RE J2107-051, EUVE J2108-05.2, 2RE J2107-051, RX J2107.9-0518, AAVSO 2102-05, GSC 05200-00849, RE J2107-05, RX J2107.9-0517, 2MASS J21075818-0517404 | |
| Database references | |
| SIMBAD | data |
HU Aquarii (abbreviated HU Aqr) is an eclipsing binary system approximately 620 light-years away from the Sun, forming a cataclysmic variable of AM Herculis-type. The two stars orbit each other every 2.08 hours and the ultra-short binary system includes an eclipsing white dwarf and red dwarf.
In 1993, Axel Schwope et al. discovered that the star, then called RXJ2107.9-0518, was both an eclipsing binary and a cataclysmic variable. The star had been flagged as a probable AM Herculis star from data collected during the ROSAT All Sky Survey. It was given its variable star designation, HU Aquarii, in 1995.