FF Aquilae
A classical Cepheid variable with a possible quadruple star system.
FF Aquilae is a classical Cepheid variable star situated in the constellation Aquila, near the border with Hercules. Its apparent magnitude shifts between 5.18 and 5.51 over a 4.47-day cycle, making it just visible to the naked eye under rural or suburban skies. Originally cataloged as HR 7165, its Cepheid variability was first identified by Charles Morse Huffer in August 1927, after which it received the designation FF Aquilae. Measurements of its brightness spanning 122 years indicate that its pulsation period is lengthening by 0.072 ± 0.011 seconds per year. As a small-amplitude classical Cepheid, it is expected to be a supergiant located near the red edge of the instability strip.
This yellow supergiant pulsates, causing changes in its temperature, diameter, and luminosity. Its distance from Earth has been estimated at 1,710 ± 60 light-years (520 ± 20 parsecs), derived from its angular diameter and inferred radius. FF Aquilae may be a quadruple star system. Spectral analysis reveals it is a spectroscopic binary, with a fainter companion—likely a main-sequence star of spectral type A9V to F3V—orbiting every 3.92 years. A third star, detected through speckle interferometry, appears to be a cooler star that has evolved off the main sequence. A fourth star, of magnitude 11.4 and located 6 arcseconds away, is slightly hotter, larger, and more luminous than the Sun and is somewhat evolved. Several studies have questioned whether this fourth star is physically bound to the system, though Gaia Data Release 3 finds it at a similar distance and with a similar proper motion.
- Apparent magnitude range
- 5.18 to 5.51
- Period
- 4.47 days
- Distance
- 1,710 ± 60 light-years (520 ± 20 parsecs)
- Spectral type of companion
- A9V to F3V
- Orbital period of binary companion
- 3.92 years
- Period increase rate
- 0.072 ± 0.011 seconds per year
- Number of possible stars in system
- 4
Lore & Background
Originally known as HR 7165, FF Aquilae 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 is a small amplitude classical Cepheid, and as such is expected to be a supergiant near the red edge of the instability strip. A yellow supergiant, FF Aquilae pulsates with varying temperature, diameter, and luminosity. It has been estimated to be 1,710 ± 60 light-years distant from Earth by extrapolating from its angular diameter and estimated radius.
Reader's Guide
FF Aquilae is significant as a classical Cepheid variable that serves as a standard candle for distance measurement, though its own distance was derived via angular diameter and estimated radius. Its period increase over 122 years provides insight into stellar evolution and the instability strip. The star is a possible quadruple system: a spectroscopic binary with a main sequence companion of spectral type A9V to F3V orbiting every 3.92 years; a third star revealed by speckle interferometry, likely a cooler evolved star; and a fourth star of magnitude 11.4 located 6 arcseconds away, somewhat evolved and slightly hotter, larger, and more luminous than the Sun. Several studies found the fourth star unlikely to be a member, though Gaia Data Release 3 finds it at a similar distance and proper motion, leaving its membership uncertain. This complexity makes FF Aquilae a valuable target for studies of multiple star systems and Cepheid properties.
Did You Know?
- It is a possible quadruple star system, with at least one spectroscopic binary companion.
- The fourth star, of magnitude 11.4, has uncertain membership despite similar distance and proper motion in Gaia Data Release 3.
More in Variable Stars, Part 3 1-24
Spotted an error? Know more?
Reader corrections go straight into our review queue. Suggest an edit · How this site is sourced