XZ Andromedae

XZ Andromedae (also known as XZ And) is a binary star in the constellation Andromeda. Its maximum apparent visual magnitude is 9.91, but drops down to 12.45 every 1.357 days. Its variability matches the behaviour of Algol variable stars.[2]

XZ Andromedae
Observation data
Epoch J2000      Equinox J2000
Constellation Andromeda
Right ascension 01h 56m 51.52427s[1]
Declination +42° 06′ 02.1813″[1]
Apparent magnitude (V) 9.91 – 12.45 variable [2]
Characteristics
Spectral type A4IV-V + G5IV[3]
Apparent magnitude (B) 10.16[4]
Apparent magnitude (V) 9.93[4]
Apparent magnitude (G) 9.9856[1]
Apparent magnitude (J) 9.373[5]
Apparent magnitude (H) 9.210[5]
Apparent magnitude (K) 9.188[5]
B−V color index 0.2125[4]
Variable type EA
Astrometry
Proper motion (μ) RA: 4.345±0.110 [1] mas/yr
Dec.: −11.814±0.116[1] mas/yr
Parallax (π)1.8406 ± 0.0788[1] mas
Distance1,770 ± 80 ly
(540 ± 20 pc)
Orbit[3]
Period (P)1.357 days
Eccentricity (e)0
Inclination (i)89°
Periastron epoch (T)HJD 2449313.53084±0.00081
Details[3]
Primary
Mass3.2 M☉
Radius2.4 R☉
Temperature9,500 K
Secondary
Mass1.3 M☉
Radius2.6 R☉
Temperature5,500 K
Other designations
2MASS J01565151+4206021, BD+41 376, TYC 2824-1360-1
Database references
SIMBADdata

System

The primary star of the system has a mass of 3.2 M☉ and has a spectral type A4IV-V, meaning that it has intermediate characteristics between a main sequence star and a subgiant one. The secondary is less massive (1.3 M☉) but larger than the primary, so it's an evolved subgiant star and its spectral type is G5IV.[3] The secondary component will likely evolve into a white dwarf before the primary leaves the main sequence.[6] Since 2019, it is suspected what the eclipsing binary is orbited by additional two similar stars in 1:3 mean-motion resonance with periods 33.43 and 100.4 years.[7]

Variability

Photometric periods of Algol variables matches the orbital period of the system. However, in XZ Andromedae have been observed slight period variations that can be reproduced with three different cycles of 137.5, 36.8 and 11.2 years, respectively. Each of them could be the effect of another faint body orbiting the binary system, but one of the two shorter cycles could also be an effect of magnetic interaction between stars (the Applegate mechanism).[3]

Other research [6] states that the long cycle is instead a long-term period increase caused by mass transfer from the secondary (that fills its Roche lobe) to the primary component.

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. XZ 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. Demircan, O.; Akalin, A.; Selam, S.; Derman, E.; Mueyesseroglu, Z. (1995). "A period study of XZ Andromedae". Astronomy and Astrophysics Supplement. 114: 167. Bibcode:1995A&AS..114..167D.
  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. Yang, Y. -G. (2013). "A new photometry and period analysis of the Algol-type binary XZ And". New Astronomy. 25: 109–113. Bibcode:2013NewA...25..109Y. doi:10.1016/j.newast.2013.05.001.
  7. A strange phenomenon of XZ Andromedae: two Keplerian periods with a 1:3 ratio, 2019, arXiv:1904.07373
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