Epoch J2000 Equinox J2000
|Right ascension||18h 58m 14.74757s|
|Declination||+17° 21′ 39.2932″|
|Apparent magnitude (V)||5.18 - 5.68|
|U−B color index||0.43|
|B−V color index||0.8|
|Variable type||Cepheid variable|
|Radial velocity (Rv)||-15.92 km/s|
|Proper motion (μ)||RA: 0.44 mas/yr
Dec.: -9.98 mas/yr
|Parallax (π)||2.11 ± 0.33 mas|
|Distance||approx. 1,500 ly
(approx. 470 pc)
|Absolute magnitude (MV)||-3.4|
FF Aquilae (CHA 82Aa) is a Delta Cephei type- or classical Cepheid variable located in the constellation Aquila. It ranges from apparent magnitude 5.18 to 5.68 over a period of 4.47 days, meaning it is visible but faint to the unaided eye in rural or suburban settings. Originally known as HR 7165, it was noted to be variable by Charles Morse Huffer in August 1927, who observed its Cepheid pattern. It then received the variable star designation FF Aquilae. Analysis of its brightness over 122 years shows that its period is increasing by 0.072 ± 0.011 seconds a per year. It has been estimated to be 1,350 light-years (413 parsecs) ± 46 light-years (14 parsecs) distant from Earth (by extrapolating from its angular diameter and estimated radius).
A yellow-white supergiant, it pulsates between spectral classes F5Ia and F8Ia, and it is on average 39 times the diameter of the Sun. Like all Cepheids, it has exhausted its core hydrogen fuel and has cooled and expanded off the main sequence—Cepheids are thought to have spent their earlier stellar lives as B-type main sequence stars before exhausting their fuel and will eventually become red giants.
Analysis of its spectrum shows that FF Aquilae is a spectroscopic binary system, the supergiant and another star, calculated to be a main sequence star of spectral type A9V to F3V, orbiting each other every 3.92 years. A third star, revealed by speckle interferometry, is likely to be a cooler star that has evolved off the main sequence. A fourth star, that is of magnitude 11.4 and located 6 arcseconds away, is unlikely to be a member of the system.
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- Bortle, John E. (February 2001). "The Bortle Dark-Sky Scale". Sky & Telescope. Sky Publishing Corporation. Retrieved 2013-02-20.
- Sanford, Roscoe F. (1935). "On the Radial-Velocity Variation of the Cepheid Variable FF Aquilae". Astrophysical Journal 81: 132–39. Bibcode:1935ApJ....81..132S. doi:10.1086/143621.
- Berdnikov, L. N.; Turner, D. G.; Henden, A. A. (2014). "A search for evolutionary period variations of Cepheids using the Harvard plate stacks: FF Aql". Astronomy Reports 58 (4): 240–48. Bibcode:2014ARep...58..240B. doi:10.1134/S1063772914040015.
- Turner, D. G.; Kovtyukh, V. V.; Luck, R. E.; Berdnikov, L. N. (2013). "The Pulsation Mode and Distance of the Cepheid FF Aquilae". The Astrophysical Journal Letters 772 (1): L10. arXiv:1306.1228. Bibcode:2013ApJ...772L..10T. doi:10.1088/2041-8205/772/1/L10.
- Malatesta, Kerri (26 February 2013). "Delta Cephei". Variable Star of the Month. Retrieved 19 July 2014.
- Evans, Nancy Remage; Welch, Douglas L.; Scarfe, Colin D.; Teays, Terry J. (1990). "The orbit and companions of the classical Cepheid FF AQL". Astronomical Journal 99: 1598–1611. Bibcode:1990AJ.....99.1598E. doi:10.1086/115442. ISSN 0004-6256.
- Udalski, A.; Evans, Nancy R. (1993). "The visual companion of the classical Cepheid FF AQL". Astronomical Journal 106 (1): 348–51. Bibcode:1993AJ....106..348U. doi:10.1086/116643. ISSN 0004-6256.