TW Andromedae

TW Andromedae (TW And) is an eclipsing binary star, classified also as an Algol variable star, in the constellation Andromeda. Its brightness varies with a period of 4.12 days, and has a typical brightness of magnitude 8.98 but decreasing down to a magnitude of 11.04 during the main eclipse.[2]

TW Andromedae
Observation data
Epoch J2000      Equinox J2000
Constellation Andromeda
Right ascension 00h 03m 18.22724s[1]
Declination +32° 50′ 45.10209″[1]
Apparent magnitude (V) 8.98 – 11.050 variable [2]
Characteristics
Spectral type F0V + K0 [2]
B−V color index 0.11[3]
Variable type EA[2]
Astrometry
Radial velocity (Rv)−51.27±0.42[4] km/s
Proper motion (μ) RA: 52.569 ± 0.053 [1] mas/yr
Dec.: -2.770 ± 0.028 [1] mas/yr
Parallax (π)3.1877 ± 0.0442[1] mas
Distance1,020 ± 10 ly
(314 ± 4 pc)
Orbit
Period (P)4.12 [5] days
Semi-major axis (a)13.6 R☉ [5]
Eccentricity (e)0.0 [6]
Inclination (i)86.9 [5]°
Periastron epoch (T)JD 2440700±300[6]
Semi-amplitude (K1)
(primary)		27±1.5[6] km/s
Semi-amplitude (K2)
(secondary)		140±2.0[6] km/s
Details
TW And A
Radius2.05[5] R☉
TW And B
Radius3.20[5] R☉
Other designations
HIP 262, 2MASS J00031822+3250451, SAO 53603, BD+32 4756, TYC 2263-975-1
Database references
SIMBADdata

System

The TW Andromedae system is made of two stars in a circular orbit around their center of mass, with an orbital plane almost parallel to our line of sight. The presence of a third body in the system, with a minimum mass of 0.27 M☉ and an orbital period of 49.6 years, has been proposed to account for the observed changes in the period of the variability.[6]

The radius of the two stars can be measured by looking at the eclipses. Beside that, little is known about the single stars, apart from their spectral types F0 and K0.

Variability

Like in all Algol variable stars, when both stars of the system are aligned with respect to our line of sight, the furthest component blocks the light of the other, thus the apparent luminosity of the system diminishes. When the brightest component eclipses the other, a secondary, less pronounced minimum in the luminosity occurs.

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.
  2. TW 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 2009-06-30.
  3. 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.
  4. 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.
  5. Rattenbury, N. J. (January 2009), "Microlensing of close binary stars", Monthly Notices of the Royal Astronomical Society, 392 (1): 439–447, arXiv:0810.2265, Bibcode:2009MNRAS.392..439R, doi:10.1111/j.1365-2966.2008.14074.x, S2CID 19012830.
  6. Kreiner, J. M.; Pribulla, T.; Tremko, J.; Stachowski, G. S.; Zakrzewski, B. (2008), "Period analysis of three close binary systems: TW And, TT Her and W UMi", Monthly Notices of the Royal Astronomical Society, 383 (4): 1506–1512, Bibcode:2008MNRAS.383.1506K, doi:10.1111/j.1365-2966.2007.12652.x.
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