Epoch J2000 Equinox J2000
|Right ascension||18h 58m 14.74757s|
|Declination||+17° 21′ 39.2932″|
|Apparent magnitude (V)||5.18 - 5.51|
|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|
|Absolute magnitude (MV)||-3.4|
FF Aquilae is a classical Cepheid variable star located in the constellation Aquila. It ranges from apparent magnitude 5.18 to 5.51 over a period of 4.470848 days, meaning it is faintly visible 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 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 supergiant, FF Aql pulsates with varying temperature, diameter, and luminosity. Like all Cepheids, it has exhausted its core hydrogen fuel, cooled and expanded off the main sequence, and is rapidly evolving towards the Asymptotic Giant Branch.
FF Aql is a possible quadruple star system. Analysis of its spectrum shows that it is a spectroscopic binary system with the fainter companion calculated to be a main sequence star of spectral type A9V to F3V, orbiting 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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