AB Andromedae

AB Andromedae (AB And) is a binary star in the constellation Andromeda. Paul Guthnick and Richard Prager discovered that the star is an eclipsing binary in 1927.^[11][12] Its maximum apparent visual magnitude is 9.49 but shows a variation in brightness down to a magnitude of 10.46 in a periodic cycle of roughly 8 hours. The observed variability is typical of W Ursae Majoris variable stars,^[3] so the two stars in this system form a contact binary.

AB Andromedae

The visual band light curve of AB Andromedae, adapted from Parimucha et al.[1]
Observation data Epoch J2000      Equinox J2000
Constellation	Andromeda
Right ascension	23h 11m 32.08609s[2]
Declination	+36° 53′ 35.10721″[2]
Apparent magnitude (V)	9.49 ( – 10.32) – 10.46[3]
Characteristics
Spectral type	G5+G5V[3]
Apparent magnitude (B)	10.62[4]
Apparent magnitude (V)	9.675[4]
Apparent magnitude (G)	9.6953[2]
Apparent magnitude (J)	8.172[5]
Apparent magnitude (H)	7.805[5]
Apparent magnitude (K)	7.665[5]
B−V color index	0.9163[4]
Variable type	EW
Astrometry
Radial velocity (Rv)	−27.53±0.67[6] km/s
Proper motion (μ)	RA: 107.923±0.046 [2] mas/yr Dec.: −53.357±0.036[2] mas/yr
Parallax (π)	11.7027±0.0367 mas[2]
Distance	278.7 ± 0.9 ly (85.5 ± 0.3 pc)
Orbit[7]
Period (P)	0.3319 days
Semi-major axis (a)	2.308 R☉[8]
Eccentricity (e)	0.002±0.001
Argument of periastron (ω) (secondary)	40±5°
Argument of periastron (ω) (primary)	220±5°
Semi-amplitude (K1) (primary)	233±1 km/s
Semi-amplitude (K2) (secondary)	133±1 km/s
Details[9]
Primary
Mass	1.04 M☉
Radius	1.03 R☉
Surface gravity (log g)	4.392[10] cgs
Temperature	5,798 K
Age	5.53±2.00[8] Gyr
Secondary
Mass	0.60 M☉
Radius	0.78 R☉
Surface gravity (log g)	4.347[10] cgs
Temperature	5,450 K
Age	5.53±2.00[8] Gyr
Other designations
2MASS J23113209+3653351, BD+36 5017, HIP 114508, SAO 73069, TYC 2763-904-1
Database references
SIMBAD	data

System

The observed spectral type of both stars in this system is G5, and one of them is a main sequence star very similar to the sun.^[3] They are orbiting so close that their envelopes touch each other. This is a dynamically stable phase that should last until one of the two stars leaves the main sequence.

The system could also host a third body with an orbital period of 19,046 days, with a minimum mass of 0.007 M_☉ and an eccentricity of 0.22, but not all data collected in time are consistent with this hypothesis.^[7]

Variability

The two stars eclipse each other during their orbit, but they have an elongated shape so they show a constant variation instead of discrete eclipses. Anyway, a periodicity can be seen clearly, but it changes with time; the period shows a long-term trend and a periodic modulation of 7,000 days. The effects responsible for this behaviour could be a third body in the system, magnetic interaction between two stars,^[9] mass transfer from one star to the other, mass loss of the system, and recently even an internal mechanism in the touching envelopes have been proposed.^[10]