FF Andromedae

FF Andromedae (often abbreviated to FF And) is a spectroscopic binary in the constellation Andromeda. It has a typical apparent visual magnitude of 10.4, but undergoes flare events that can increase its brightness by about a magnitude.

FF Andromedae
Observation data
Epoch J2000      Equinox J2000
Constellation Andromeda
Right ascension 00h 42m 48.24949s[1]
Declination +35° 32′ 55.65804″[1]
Apparent magnitude (V) 10.428 variable[2]
Characteristics
Spectral type M1Ve+M1Ve[3]
Apparent magnitude (B) 11.84[4]
Apparent magnitude (V) 10.428[2]
Apparent magnitude (R) 9.941[2]
Apparent magnitude (I) 8.8[5]
Apparent magnitude (G) 9.5526[1]
Apparent magnitude (J) 7.164[6]
Apparent magnitude (H) 6.506[6]
Apparent magnitude (K) 6.321[6]
Variable type BY Dra + Flare
Astrometry
Radial velocity (Rv)−0.47±0.90[7] km/s
Proper motion (μ) RA: 262.064±0.074 [1] mas/yr
Dec.: 77.062±0.109[1] mas/yr
Parallax (π)46.0337 ± 0.0542[1] mas
Distance70.85 ± 0.08 ly
(21.72 ± 0.03 pc)
Orbit
Period (P)2.17 days[8]
Details
FF Andromedae A
Mass0.763[9] M☉
Radius0.767[9] R☉
Temperature3,464[8] K
Metallicity [Fe/H]+0.101[8] dex
Rotation2.170 days[9]
Rotational velocity (v sin i)7.8[8] km/s
FF Andromedae B
Radius0.757[8] R☉
Temperature3,464[8] K
Metallicity [Fe/H]+0.101[8] dex
Rotational velocity (v sin i)6.6[8] km/s
Age55[8] Myr
Other designations
2MASS J00424820+3532554, BD+34 106, HIP 3362, GJ 29.1, TYC 2283-26-1, NLTT 2314, WDS J00428+3533A
Database references
SIMBADdata

System

Both stars in the FF Andromedae system are main sequence red dwarfs of spectral type M1Ve, meaning that the spectrum shows strong emission lines. The lines identified are H-alpha and CaII. They have a total mass of 1.10 M☉ and both are tidally locked, thus their rotation period is equal to the orbital period of 2.17 days.[8]

The secondary component should not be confused with the 13th magnitude star listed in the Washington Double Star Catalog as WDS J00428+3533B and sometimes referred to as GJ 29.1B,[10] which is just a line-of-sight giant star much more distant than FF Andromedae.[11] The designation GJ 29.1B is also applied to the secondary red dwarf in the close spectroscopic binary.[8]

Variability

FF Andromedae shows a regular variability within a rotation period, typical of BY Draconis variable stars, but occasionally increases its brightness in a stellar flare. Small amplitude variations, at timescales of several minutes, were also reported during the quiescent phase. Small, but highly significant dips in the light curve have been detected approximately 25 minutes before a large flare.[12]

References
  1. Brown, A. G. A.; et al. (Gaia collaboration) (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics. 616. A1. arXiv:1804.09365. Bibcode:2018A&A...616A...1G. doi:10.1051/0004-6361/201833051. Gaia DR2 record for this source at VizieR.
  2. Database entry, VizieR Online Data Catalog: UCAC4 Catalogue (Zacharias+, 2012), N. Zacharias et al., CDS ID I/322A Accessed on line 2018-11-06.
  3. FF And, database entry, Combined General Catalog of Variable Stars (GCVS4.2, 2004 Ed.), N. N. Samus, O. V. Durlevich, et al., CDS ID II/250 Accessed on line 2018-10-17.
  4. "FF And". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved November 6, 2018.
  5. Database entry, VizieR Online Data Catalog: The USNO-B1.0 Catalog (Monet+ 2003), D. G. Monet et al., CDS ID I/284 Accessed on line 2018-11-06.
  6. Cutri, R. M.; Skrutskie, M. F.; Van Dyk, S.; et al. (June 2003). "VizieR Online Data Catalog: 2MASS All-Sky Catalog of Point Sources (Cutri+ 2003)". CDS/ADC Collection of Electronic Catalogues (2246): II/246. Bibcode:2003yCat.2246....0C.
  7. de Bruijne, J. H. J.; Eilers, A.-C. (October 2012), "Radial velocities for the HIPPARCOS-Gaia Hundred-Thousand-Proper-Motion project", Astronomy & Astrophysics, 546: 14, arXiv:1208.3048, Bibcode:2012A&A...546A..61D, doi:10.1051/0004-6361/201219219, S2CID 59451347, A61.
  8. Houdebine, E. R. (August 2009). "Observation and modelling of main-sequence star chromospheres - XII. Two-component model chromospheres for five active dM1e stars". Monthly Notices of the Royal Astronomical Society. 397 (4): 2133–2147. Bibcode:2009MNRAS.397.2133H. doi:10.1111/j.1365-2966.2009.15112.x.
  9. Newton, E. R.; Irwin, J.; Charbonneau, D.; Berlind, P.; Calkins, M. L.; Mink, J. (2017), "The Hα Emission of Nearby M Dwarfs and its Relation to Stellar Rotation", The Astrophysical Journal, 834 (1): 85, Bibcode:2017ApJ...834...85N, doi:10.3847/1538-4357/834/1/85, hdl:1721.1/109733, S2CID 55000202.
  10. "GJ 29.1 B". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved November 6, 2018.
  11. Brown, A. G. A.; et al. (Gaia collaboration) (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics. 616. A1. arXiv:1804.09365. Bibcode:2018A&A...616A...1G. doi:10.1051/0004-6361/201833051. Gaia DR2 record for this source at VizieR.
  12. Peres, G.; Ventura, R.; Pagano, I.; Rodono, M. (1993), "Low amplitude variability and transient periodicity in FF Andromedae and other active stars.", Astronomy & Astrophysics, 278: 179–186, Bibcode:1993A&A...278..179P.
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