FO Aquarii is an intermediate polar[4] star system in the constellation Aquarius. The white dwarf and companion star orbit each other with a period of approximately 4.85 hours.[5] The system is famous for a very strong optical pulsation which occurs every 20.9 minutes, corresponding with the rotational period of the accreting white dwarf.[6] Prior to 2016, the system's long-term optical brightness varied between apparent magnitude 12.7 and 14.2,[7] but in early 2016, it faded to magnitude 15.8 and thereafter began a slow recovery to its normal brightness, behavior which is indicative of a temporary dropoff in the mass-transfer rate between the two stars.[8]
 The visual band light curve of FO Aquarii. The main plot shows the dimming which occurred in 2016, and the inset plot shows the short-term variation that occurs during an orbital period. Adapted from Littlefield et al. (2016)[1] | |
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Aquarius |
| Right ascension | 22h 17m 55.38s[2] |
| Declination | −08° 21′ 04.6″[2] |
| Apparent magnitude (V) | 12.7[3] |
| Characteristics | |
| Apparent magnitude (B) | 13.70[2] |
| Apparent magnitude (R) | 13.60[2] |
| Apparent magnitude (J) | 12.87[2] |
| Apparent magnitude (H) | 12.75[2] |
| Apparent magnitude (K) | 12.51[2] |
| Variable type | DQ[4] |
| Orbit | |
| Period (P) | 4.85 hr[5] |
| Other designations | |
| Database references | |
| SIMBAD | data |
| Data sources: | |
| Hipparcos Catalogue, CCDM (2002), Bright Star Catalogue (5th rev. ed.) | |