FF Aquilae

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FF Aquilae
Observation data
Epoch J2000      Equinox J2000
Constellation Aquila
Right ascension 18h 58m 14.74757s
Declination +17° 21′ 39.2932″
Apparent magnitude (V) 5.18 - 5.51[1]
Spectral type F6Ib[2]
U−B color index 0.43[3]
B−V color index 0.8[3]
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[4] ± 0.33 mas
Distance 413[5] pc
Absolute magnitude (MV) -3.4[5]
Mass 3.2[6] M
Radius 39[5] R
Temperature 6,195[5] K
Other designations
FF Aql, HD 176155, HIP 93124, BD+17° 3799, HR 7165, SAO 104296.
Database references

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,[1] meaning it is faintly visible to the unaided eye in rural or suburban settings.[7] 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.[8] Analysis of its brightness over 122 years shows that its period is increasing by 0.072 ± 0.011 seconds per year.[9] 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).[5]

A yellow supergiant, FF Aql pulsates with varying temperature, diameter, and luminosity.[5] 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.[10] A fourth star, that is of magnitude 11.4 and located 6 arcseconds away, is unlikely to be a member of the system.[6][11]


  1. ^ a b Watson, Christopher (4 January 2010). "FF Aquilae". AAVSO Website. American Association of Variable Star Observers. Retrieved 18 July 2014. 
  2. ^ Abt, Helmut A. (2009). "MK Classifications of Spectroscopic Binaries". The Astrophysical Journal Supplement. 180: 117. Bibcode:2009ApJS..180..117A. doi:10.1088/0067-0049/180/1/117. 
  3. ^ a b Ducati, J. R. (2002). "VizieR Online Data Catalog: Catalogue of Stellar Photometry in Johnson's 11-color system". CDS/ADC Collection of Electronic Catalogues. 2237: 0. Bibcode:2002yCat.2237....0D. 
  4. ^ Van Leeuwen, F. (2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics. 474 (2): 653–664. Bibcode:2007A&A...474..653V. arXiv:0708.1752Freely accessible. doi:10.1051/0004-6361:20078357. 
  5. ^ a b c d e f 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. 772: L10. Bibcode:2013ApJ...772L..10T. arXiv:1306.1228Freely accessible. doi:10.1088/2041-8205/772/1/L10. 
  6. ^ a b Gallenne, A.; Kervella, P.; Mérand, A.; Evans, N. R.; Girard, J. H. V.; Gieren, W.; Pietrzyński, G. (2014). "Searching for visual companions of close Cepheids". Astronomy & Astrophysics. 567: A60. Bibcode:2014A&A...567A..60G. arXiv:1406.0493Freely accessible. doi:10.1051/0004-6361/201423872. 
  7. ^ Bortle, John E. (2001). "Introducing the Bortle Dark-Sky Scale". Sky and Telescope. 101: 126. Bibcode:2001S&T...101b.126B. 
  8. ^ 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. 
  9. ^ 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. 
  10. ^ 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. ISSN 0004-6256. doi:10.1086/115442. 
  11. ^ 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. ISSN 0004-6256. doi:10.1086/116643.