AC Andromedae

AC Andromedae (AC And) is a variable star in the constellation Andromeda. Its maximum apparent visual magnitude is 10.77, but can be seen fainter down to a magnitude of 11.9.[2]

AC Andromedae
Observation data
Epoch J2000      Equinox J2000
Constellation Andromeda
Right ascension  23h 18m 02.34635s[1]
Declination +48° 46′ 58.33955″[1]
Apparent magnitude (V) 10.7 – 11.9 variable [2]
Characteristics
Spectral type F5[3]
Apparent magnitude (B) 11.48[4]
Apparent magnitude (V) 10.90[4]
Apparent magnitude (G) 10.9002[1]
Apparent magnitude (J) 9.646[5]
Apparent magnitude (H) 9.483[5]
Apparent magnitude (K) 9.345[5]
B−V color index 0.5389[4]
Variable type Peculiar[2]
Astrometry
Radial velocity (Rv)−50.0±2.8[6] km/s
Proper motion (μ) RA: −2.342±0.049 [1] mas/yr
Dec.: −2.285±0.048[1] mas/yr
Parallax (π)0.5315 ± 0.0315[1] mas
Distance6,100 ± 400 ly
(1,900 ± 100 pc)
Other designations
2MASS J23180234+4846582, BD+47 4104, HIP 115046, TYC 3644-2114-1
Database references
SIMBADdata

The nature of AC Andromedae is still not determined. Its light curve shows clearly three radial pulsation modes, the fundamental one with a period of 0.71 days, and the first two overtones of 0.525 and 0.421 days, respectively. It is then unclear if it belongs to the class of RR Lyrae variables or to the one of Delta Scuti variables.[7][8] Another study points at AC And as an intermediate object between classical Cepheids and Delta Scuti variables.[3] The physical parameters of the star itself would be different depending on which class it belongs to.

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. AC 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.
  3. Fernie, J. D. (November 1994), "AC Andromedae: the missing link between δ Scuti stars and classical Cepheids?", Monthly Notices of the Royal Astronomical Society, 271: L19–L20, Bibcode:1994MNRAS.271L..19F, doi:10.1093/mnras/271.1.L19.
  4. Høg, E.; Fabricius, C.; Makarov, V. V.; Urban, S.; Corbin, T.; Wycoff, G.; Bastian, U.; Schwekendiek, P.; Wicenec, A. (2000), "The Tycho-2 catalogue of the 2.5 million brightest stars", Astronomy & Astrophysics, 355: L27–L30, Bibcode:2000A&A...355L..27H.
  5. 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.
  6. Gontcharov, G. A. (November 2006), "Pulkovo Compilation of Radial Velocities for 35495 Hipparcos stars in a common system", Astronomy Letters, 32 (11): 759–771, arXiv:1606.08053, Bibcode:2006AstL...32..759G, doi:10.1134/S1063773706110065.
  7. Fitch, W. S.; Szeidl, B. (February 1976), "The three radial modes and evolutionary state of AC Andromedae.", Astrophysical Journal, 203: 616–624, Bibcode:1976ApJ...203..616F, doi:10.1086/154120.
  8. Petersen, J. O. (May 1978), "An interpretation of the unique triple mode variable AC Andromedae as an RR Lyrae type star oscillating in the first three radial over-tones.", Astronomy and Astrophysics, 65: 616–624, Bibcode:1978A&A....65..451P.
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