FO Aquarii

FO Aquarii is an intermediate polar[3] star system in the constellation Aquarius. The white dwarf and companion star orbit each other with a period of approximately 4.85 hours.[4] 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.[5] Prior to 2016, the system's long-term optical brightness varied between apparent magnitude 12.7 and 14.2,[6] 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.[7]

FO Aquarii
Observation data
Epoch J2000      Equinox J2000
Constellation Aquarius
Right ascension  22h 17m 55.38s[1]
Declination −08° 21′ 04.6″[1]
Apparent magnitude (V) 12.7[2]
Characteristics
Apparent magnitude (B) 13.70[1]
Apparent magnitude (R) 13.60[1]
Apparent magnitude (J) 12.87[1]
Apparent magnitude (H) 12.75[1]
Apparent magnitude (K) 12.51[1]
Variable type DQ[3]
Orbit
Period (P)4.85 hr[4]
Other designations
2E 4588, 1RXS J221753.9-082115, CS 22886-0021, H 2215-086
Database references
SIMBADdata
Data sources:
Hipparcos Catalogue,
CCDM (2002),
Bright Star Catalogue (5th rev. ed.)

References
  1. Cutri, R. M.; Skrutskie, M. F.; van Dyk, S.; Beichman, C. A.; Carpenter, J. M.; Chester, T.; Cambresy, L.; Evans, T.; Fowler, J.; Gizis, J.; Howard, E.; Huchra, J.; Jarrett, T.; Kopan, E. L.; Kirkpatrick, J. D.; Light, R. M.; Marsh, K. A.; McCallon, H.; Schneider, S.; Stiening, R.; Sykes, M.; Weinberg, M.; Wheaton, W. A.; Wheelock, S.; Zacarias, N. (2003). "2MASS All-Sky Catalog of Point Sources (Cutri+ 2003)". University of Massachusetts and Infrared Processing and Analysis Center. IPAC/California Institute of Technology. Bibcode:2003yCat.2246....0C.
  2. Samus’, N. N.; Goranskii, V. P.; Durlevich, O. V.; Zharova, A. V.; Kazarovets, E. V.; Kireeva, N. N.; Pastukhova, E. N.; Williams, D. B.; Hazen, M. L. (2003). "An electronic version of the second volume of the General Catalogue of Variable Stars with improved coordinates". Astronomy Letters. 29 (7): 468–479. Bibcode:2003AstL...29..468S. doi:10.1134/1.1589864.
  3. Pekön, Y.; Balman, Ş. (2012). "Orbital-phase-resolved Spectroscopy of the Intermediate Polar FO Aqr Using XMM-Newton Observatory Data". The Astronomical Journal. 144 (2): 53. arXiv:1206.2215. Bibcode:2012AJ....144...53P. doi:10.1088/0004-6256/144/2/53.
  4. Osborne, J.; Mukai, K. (1989). "New Orbital and Spin Ephemerides of the Intermediate Polar Fo-Aquarii = H:2215-086". Monthly Notices of the Royal Astronomical Society. 238 (3): 1233–1246. Bibcode:1989MNRAS.238.1233O. doi:10.1093/mnras/238.4.1233.
  5. Patterson, J.; Steiner, J. E. (1983-01-01). "H2215-086 -King of the DQ Herculis stars". The Astrophysical Journal. 264: L61. Bibcode:1983ApJ...264L..61P. doi:10.1086/183944. ISSN 0004-637X.
  6. VSX; Otero, S. A. (24 May 2011). "FO Aquarii". AAVSO Website. American Association of Variable Star Observers. Retrieved 10 October 2014.
  7. Littlefield, Colin; Garnavich, Peter; Kennedy, Mark R.; Aadland, Erin; Terndrup, Donald M.; Calhoun, Grace V.; Callanan, Paul; Abe, Lyu; Bendjoya, Philippe (2016-01-01). "Return of the King: Time-series Photometry of FO Aquarii's Initial Recovery from its Unprecedented 2016 Low State". The Astrophysical Journal. 833 (1): 93. arXiv:1609.01026. Bibcode:2016ApJ...833...93L. doi:10.3847/1538-4357/833/1/93. ISSN 0004-637X.
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